1 /*
   2  * Copyright (c) 1994, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package java.lang;
  26 
  27 import java.io.BufferedInputStream;
  28 import java.io.BufferedOutputStream;
  29 import java.io.Console;
  30 import java.io.FileDescriptor;
  31 import java.io.FileInputStream;
  32 import java.io.FileOutputStream;
  33 import java.io.IOException;
  34 import java.io.InputStream;
  35 import java.io.PrintStream;
  36 import java.io.UnsupportedEncodingException;
  37 import java.lang.annotation.Annotation;
  38 import java.lang.module.ModuleDescriptor;
  39 import java.lang.reflect.Constructor;
  40 import java.lang.reflect.Executable;
  41 import java.lang.reflect.Method;
  42 import java.lang.reflect.Modifier;
  43 import java.net.URI;
  44 import java.nio.charset.CharacterCodingException;
  45 import java.security.AccessControlContext;
  46 import java.security.ProtectionDomain;
  47 import java.security.AccessController;
  48 import java.security.PrivilegedAction;
  49 import java.nio.channels.Channel;
  50 import java.nio.channels.spi.SelectorProvider;
  51 import java.nio.charset.Charset;
  52 import java.util.Iterator;
  53 import java.util.List;
  54 import java.util.Map;
  55 import java.util.Objects;
  56 import java.util.Properties;
  57 import java.util.PropertyPermission;
  58 import java.util.ResourceBundle;
  59 import java.util.concurrent.Callable;
  60 import java.util.function.Supplier;
  61 import java.util.concurrent.ConcurrentHashMap;
  62 import java.util.stream.Stream;
  63 
  64 import jdk.internal.util.StaticProperty;
  65 import jdk.internal.module.ModuleBootstrap;
  66 import jdk.internal.module.ServicesCatalog;
  67 import jdk.internal.reflect.CallerSensitive;
  68 import jdk.internal.reflect.Reflection;
  69 import jdk.internal.HotSpotIntrinsicCandidate;
  70 import jdk.internal.access.JavaLangAccess;
  71 import jdk.internal.access.SharedSecrets;
  72 import jdk.internal.misc.VM;
  73 import jdk.internal.logger.LoggerFinderLoader;
  74 import jdk.internal.logger.LazyLoggers;
  75 import jdk.internal.logger.LocalizedLoggerWrapper;
  76 import jdk.internal.util.SystemProps;
  77 import jdk.internal.vm.annotation.Stable;
  78 import sun.reflect.annotation.AnnotationType;
  79 import sun.nio.ch.Interruptible;
  80 import sun.security.util.SecurityConstants;
  81 
  82 /**
  83  * The {@code System} class contains several useful class fields
  84  * and methods. It cannot be instantiated.
  85  *
  86  * Among the facilities provided by the {@code System} class
  87  * are standard input, standard output, and error output streams;
  88  * access to externally defined properties and environment
  89  * variables; a means of loading files and libraries; and a utility
  90  * method for quickly copying a portion of an array.
  91  *
  92  * @since   1.0
  93  */
  94 public final class System {
  95     /* Register the natives via the static initializer.
  96      *
  97      * VM will invoke the initializeSystemClass method to complete
  98      * the initialization for this class separated from clinit.
  99      * Note that to use properties set by the VM, see the constraints
 100      * described in the initializeSystemClass method.
 101      */
 102     private static native void registerNatives();
 103     static {
 104         registerNatives();
 105     }
 106 
 107     /** Don't let anyone instantiate this class */
 108     private System() {
 109     }
 110 
 111     /**
 112      * The "standard" input stream. This stream is already
 113      * open and ready to supply input data. Typically this stream
 114      * corresponds to keyboard input or another input source specified by
 115      * the host environment or user.
 116      */
 117     public static final InputStream in = null;
 118 
 119     /**
 120      * The "standard" output stream. This stream is already
 121      * open and ready to accept output data. Typically this stream
 122      * corresponds to display output or another output destination
 123      * specified by the host environment or user.
 124      * <p>
 125      * For simple stand-alone Java applications, a typical way to write
 126      * a line of output data is:
 127      * <blockquote><pre>
 128      *     System.out.println(data)
 129      * </pre></blockquote>
 130      * <p>
 131      * See the {@code println} methods in class {@code PrintStream}.
 132      *
 133      * @see     java.io.PrintStream#println()
 134      * @see     java.io.PrintStream#println(boolean)
 135      * @see     java.io.PrintStream#println(char)
 136      * @see     java.io.PrintStream#println(char[])
 137      * @see     java.io.PrintStream#println(double)
 138      * @see     java.io.PrintStream#println(float)
 139      * @see     java.io.PrintStream#println(int)
 140      * @see     java.io.PrintStream#println(long)
 141      * @see     java.io.PrintStream#println(java.lang.Object)
 142      * @see     java.io.PrintStream#println(java.lang.String)
 143      */
 144     public static final PrintStream out = null;
 145 
 146     /**
 147      * The "standard" error output stream. This stream is already
 148      * open and ready to accept output data.
 149      * <p>
 150      * Typically this stream corresponds to display output or another
 151      * output destination specified by the host environment or user. By
 152      * convention, this output stream is used to display error messages
 153      * or other information that should come to the immediate attention
 154      * of a user even if the principal output stream, the value of the
 155      * variable {@code out}, has been redirected to a file or other
 156      * destination that is typically not continuously monitored.
 157      */
 158     public static final PrintStream err = null;
 159 
 160     // indicates if a security manager is possible
 161     private static final int NEVER = 1;
 162     private static final int MAYBE = 2;
 163     private static @Stable int allowSecurityManager;
 164 
 165     // current security manager
 166     private static volatile SecurityManager security;   // read by VM
 167 
 168     // return true if a security manager is allowed
 169     private static boolean allowSecurityManager() {
 170         return (allowSecurityManager != NEVER);
 171     }
 172 
 173     /**
 174      * Reassigns the "standard" input stream.
 175      *
 176      * First, if there is a security manager, its {@code checkPermission}
 177      * method is called with a {@code RuntimePermission("setIO")} permission
 178      *  to see if it's ok to reassign the "standard" input stream.
 179      *
 180      * @param in the new standard input stream.
 181      *
 182      * @throws SecurityException
 183      *        if a security manager exists and its
 184      *        {@code checkPermission} method doesn't allow
 185      *        reassigning of the standard input stream.
 186      *
 187      * @see SecurityManager#checkPermission
 188      * @see java.lang.RuntimePermission
 189      *
 190      * @since   1.1
 191      */
 192     public static void setIn(InputStream in) {
 193         checkIO();
 194         setIn0(in);
 195     }
 196 
 197     /**
 198      * Reassigns the "standard" output stream.
 199      *
 200      * First, if there is a security manager, its {@code checkPermission}
 201      * method is called with a {@code RuntimePermission("setIO")} permission
 202      *  to see if it's ok to reassign the "standard" output stream.
 203      *
 204      * @param out the new standard output stream
 205      *
 206      * @throws SecurityException
 207      *        if a security manager exists and its
 208      *        {@code checkPermission} method doesn't allow
 209      *        reassigning of the standard output stream.
 210      *
 211      * @see SecurityManager#checkPermission
 212      * @see java.lang.RuntimePermission
 213      *
 214      * @since   1.1
 215      */
 216     public static void setOut(PrintStream out) {
 217         checkIO();
 218         setOut0(out);
 219     }
 220 
 221     /**
 222      * Reassigns the "standard" error output stream.
 223      *
 224      * First, if there is a security manager, its {@code checkPermission}
 225      * method is called with a {@code RuntimePermission("setIO")} permission
 226      *  to see if it's ok to reassign the "standard" error output stream.
 227      *
 228      * @param err the new standard error output stream.
 229      *
 230      * @throws SecurityException
 231      *        if a security manager exists and its
 232      *        {@code checkPermission} method doesn't allow
 233      *        reassigning of the standard error output stream.
 234      *
 235      * @see SecurityManager#checkPermission
 236      * @see java.lang.RuntimePermission
 237      *
 238      * @since   1.1
 239      */
 240     public static void setErr(PrintStream err) {
 241         checkIO();
 242         setErr0(err);
 243     }
 244 
 245     private static volatile Console cons;
 246 
 247     /**
 248      * Returns the unique {@link java.io.Console Console} object associated
 249      * with the current Java virtual machine, if any.
 250      *
 251      * @return  The system console, if any, otherwise {@code null}.
 252      *
 253      * @since   1.6
 254      */
 255      public static Console console() {
 256          Console c;
 257          if ((c = cons) == null) {
 258              synchronized (System.class) {
 259                  if ((c = cons) == null) {
 260                      cons = c = SharedSecrets.getJavaIOAccess().console();
 261                  }
 262              }
 263          }
 264          return c;
 265      }
 266 
 267     /**
 268      * Returns the channel inherited from the entity that created this
 269      * Java virtual machine.
 270      *
 271      * This method returns the channel obtained by invoking the
 272      * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel
 273      * inheritedChannel} method of the system-wide default
 274      * {@link java.nio.channels.spi.SelectorProvider} object.
 275      *
 276      * <p> In addition to the network-oriented channels described in
 277      * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel
 278      * inheritedChannel}, this method may return other kinds of
 279      * channels in the future.
 280      *
 281      * @return  The inherited channel, if any, otherwise {@code null}.
 282      *
 283      * @throws  IOException
 284      *          If an I/O error occurs
 285      *
 286      * @throws  SecurityException
 287      *          If a security manager is present and it does not
 288      *          permit access to the channel.
 289      *
 290      * @since 1.5
 291      */
 292     public static Channel inheritedChannel() throws IOException {
 293         return SelectorProvider.provider().inheritedChannel();
 294     }
 295 
 296     private static void checkIO() {
 297         SecurityManager sm = getSecurityManager();
 298         if (sm != null) {
 299             sm.checkPermission(new RuntimePermission("setIO"));
 300         }
 301     }
 302 
 303     private static native void setIn0(InputStream in);
 304     private static native void setOut0(PrintStream out);
 305     private static native void setErr0(PrintStream err);
 306 
 307     /**
 308      * Sets the system-wide security manager.
 309      *
 310      * If there is a security manager already installed, this method first
 311      * calls the security manager's {@code checkPermission} method
 312      * with a {@code RuntimePermission("setSecurityManager")}
 313      * permission to ensure it's ok to replace the existing
 314      * security manager.
 315      * This may result in throwing a {@code SecurityException}.
 316      *
 317      * <p> Otherwise, the argument is established as the current
 318      * security manager. If the argument is {@code null} and no
 319      * security manager has been established, then no action is taken and
 320      * the method simply returns.
 321      *
 322      * @implNote In the JDK implementation, if the Java virtual machine is
 323      * started with the system property {@code java.security.manager} set to
 324      * the special token "{@code disallow}" then the {@code setSecurityManager}
 325      * method cannot be used to set a security manager.
 326      *
 327      * @param  sm the security manager or {@code null}
 328      * @throws SecurityException
 329      *         if the security manager has already been set and its {@code
 330      *         checkPermission} method doesn't allow it to be replaced
 331      * @throws UnsupportedOperationException
 332      *         if {@code sm} is non-null and a security manager is not allowed
 333      *         to be set dynamically
 334      * @see #getSecurityManager
 335      * @see SecurityManager#checkPermission
 336      * @see java.lang.RuntimePermission
 337      */
 338     public static void setSecurityManager(SecurityManager sm) {
 339         if (allowSecurityManager()) {
 340             if (security == null) {
 341                 // ensure image reader is initialized
 342                 Object.class.getResource("java/lang/ANY");
 343             }
 344             if (sm != null) {
 345                 try {
 346                     // pre-populates the SecurityManager.packageAccess cache
 347                     // to avoid recursive permission checking issues with custom
 348                     // SecurityManager implementations
 349                     sm.checkPackageAccess("java.lang");
 350                 } catch (Exception e) {
 351                     // no-op
 352                 }
 353             }
 354             setSecurityManager0(sm);
 355         } else {
 356             // security manager not allowed
 357             if (sm != null) {
 358                 throw new UnsupportedOperationException(
 359                     "Runtime configured to disallow security manager");
 360             }
 361         }
 362     }
 363 
 364     private static synchronized
 365     void setSecurityManager0(final SecurityManager s) {
 366         SecurityManager sm = getSecurityManager();
 367         if (sm != null) {
 368             // ask the currently installed security manager if we
 369             // can replace it.
 370             sm.checkPermission(new RuntimePermission("setSecurityManager"));
 371         }
 372 
 373         if ((s != null) && (s.getClass().getClassLoader() != null)) {
 374             // New security manager class is not on bootstrap classpath.
 375             // Force policy to get initialized before we install the new
 376             // security manager, in order to prevent infinite loops when
 377             // trying to initialize the policy (which usually involves
 378             // accessing some security and/or system properties, which in turn
 379             // calls the installed security manager's checkPermission method
 380             // which will loop infinitely if there is a non-system class
 381             // (in this case: the new security manager class) on the stack).
 382             AccessController.doPrivileged(new PrivilegedAction<>() {
 383                 public Object run() {
 384                     s.getClass().getProtectionDomain().implies
 385                         (SecurityConstants.ALL_PERMISSION);
 386                     return null;
 387                 }
 388             });
 389         }
 390 
 391         security = s;
 392     }
 393 
 394     /**
 395      * Gets the system-wide security manager.
 396      *
 397      * @return  if a security manager has already been established for the
 398      *          current application, then that security manager is returned;
 399      *          otherwise, {@code null} is returned.
 400      * @see     #setSecurityManager
 401      */
 402     public static SecurityManager getSecurityManager() {
 403         if (allowSecurityManager()) {
 404             return security;
 405         } else {
 406             return null;
 407         }
 408     }
 409 
 410     /**
 411      * Returns the current time in milliseconds.  Note that
 412      * while the unit of time of the return value is a millisecond,
 413      * the granularity of the value depends on the underlying
 414      * operating system and may be larger.  For example, many
 415      * operating systems measure time in units of tens of
 416      * milliseconds.
 417      *
 418      * <p> See the description of the class {@code Date} for
 419      * a discussion of slight discrepancies that may arise between
 420      * "computer time" and coordinated universal time (UTC).
 421      *
 422      * @return  the difference, measured in milliseconds, between
 423      *          the current time and midnight, January 1, 1970 UTC.
 424      * @see     java.util.Date
 425      */
 426     @HotSpotIntrinsicCandidate
 427     public static native long currentTimeMillis();
 428 
 429     /**
 430      * Returns the current value of the running Java Virtual Machine's
 431      * high-resolution time source, in nanoseconds.
 432      *
 433      * This method can only be used to measure elapsed time and is
 434      * not related to any other notion of system or wall-clock time.
 435      * The value returned represents nanoseconds since some fixed but
 436      * arbitrary <i>origin</i> time (perhaps in the future, so values
 437      * may be negative).  The same origin is used by all invocations of
 438      * this method in an instance of a Java virtual machine; other
 439      * virtual machine instances are likely to use a different origin.
 440      *
 441      * <p>This method provides nanosecond precision, but not necessarily
 442      * nanosecond resolution (that is, how frequently the value changes)
 443      * - no guarantees are made except that the resolution is at least as
 444      * good as that of {@link #currentTimeMillis()}.
 445      *
 446      * <p>Differences in successive calls that span greater than
 447      * approximately 292 years (2<sup>63</sup> nanoseconds) will not
 448      * correctly compute elapsed time due to numerical overflow.
 449      *
 450      * <p>The values returned by this method become meaningful only when
 451      * the difference between two such values, obtained within the same
 452      * instance of a Java virtual machine, is computed.
 453      *
 454      * <p>For example, to measure how long some code takes to execute:
 455      * <pre> {@code
 456      * long startTime = System.nanoTime();
 457      * // ... the code being measured ...
 458      * long elapsedNanos = System.nanoTime() - startTime;}</pre>
 459      *
 460      * <p>To compare elapsed time against a timeout, use <pre> {@code
 461      * if (System.nanoTime() - startTime >= timeoutNanos) ...}</pre>
 462      * instead of <pre> {@code
 463      * if (System.nanoTime() >= startTime + timeoutNanos) ...}</pre>
 464      * because of the possibility of numerical overflow.
 465      *
 466      * @return the current value of the running Java Virtual Machine's
 467      *         high-resolution time source, in nanoseconds
 468      * @since 1.5
 469      */
 470     @HotSpotIntrinsicCandidate
 471     public static native long nanoTime();
 472 
 473     /**
 474      * Copies an array from the specified source array, beginning at the
 475      * specified position, to the specified position of the destination array.
 476      * A subsequence of array components are copied from the source
 477      * array referenced by {@code src} to the destination array
 478      * referenced by {@code dest}. The number of components copied is
 479      * equal to the {@code length} argument. The components at
 480      * positions {@code srcPos} through
 481      * {@code srcPos+length-1} in the source array are copied into
 482      * positions {@code destPos} through
 483      * {@code destPos+length-1}, respectively, of the destination
 484      * array.
 485      * <p>
 486      * If the {@code src} and {@code dest} arguments refer to the
 487      * same array object, then the copying is performed as if the
 488      * components at positions {@code srcPos} through
 489      * {@code srcPos+length-1} were first copied to a temporary
 490      * array with {@code length} components and then the contents of
 491      * the temporary array were copied into positions
 492      * {@code destPos} through {@code destPos+length-1} of the
 493      * destination array.
 494      * <p>
 495      * If {@code dest} is {@code null}, then a
 496      * {@code NullPointerException} is thrown.
 497      * <p>
 498      * If {@code src} is {@code null}, then a
 499      * {@code NullPointerException} is thrown and the destination
 500      * array is not modified.
 501      * <p>
 502      * Otherwise, if any of the following is true, an
 503      * {@code ArrayStoreException} is thrown and the destination is
 504      * not modified:
 505      * <ul>
 506      * <li>The {@code src} argument refers to an object that is not an
 507      *     array.
 508      * <li>The {@code dest} argument refers to an object that is not an
 509      *     array.
 510      * <li>The {@code src} argument and {@code dest} argument refer
 511      *     to arrays whose component types are different primitive types.
 512      * <li>The {@code src} argument refers to an array with a primitive
 513      *    component type and the {@code dest} argument refers to an array
 514      *     with a reference component type.
 515      * <li>The {@code src} argument refers to an array with a reference
 516      *    component type and the {@code dest} argument refers to an array
 517      *     with a primitive component type.
 518      * </ul>
 519      * <p>
 520      * Otherwise, if any of the following is true, an
 521      * {@code IndexOutOfBoundsException} is
 522      * thrown and the destination is not modified:
 523      * <ul>
 524      * <li>The {@code srcPos} argument is negative.
 525      * <li>The {@code destPos} argument is negative.
 526      * <li>The {@code length} argument is negative.
 527      * <li>{@code srcPos+length} is greater than
 528      *     {@code src.length}, the length of the source array.
 529      * <li>{@code destPos+length} is greater than
 530      *     {@code dest.length}, the length of the destination array.
 531      * </ul>
 532      * <p>
 533      * Otherwise, if any actual component of the source array from
 534      * position {@code srcPos} through
 535      * {@code srcPos+length-1} cannot be converted to the component
 536      * type of the destination array by assignment conversion, an
 537      * {@code ArrayStoreException} is thrown. In this case, let
 538      * <b><i>k</i></b> be the smallest nonnegative integer less than
 539      * length such that {@code src[srcPos+}<i>k</i>{@code ]}
 540      * cannot be converted to the component type of the destination
 541      * array; when the exception is thrown, source array components from
 542      * positions {@code srcPos} through
 543      * {@code srcPos+}<i>k</i>{@code -1}
 544      * will already have been copied to destination array positions
 545      * {@code destPos} through
 546      * {@code destPos+}<i>k</I>{@code -1} and no other
 547      * positions of the destination array will have been modified.
 548      * (Because of the restrictions already itemized, this
 549      * paragraph effectively applies only to the situation where both
 550      * arrays have component types that are reference types.)
 551      *
 552      * @param      src      the source array.
 553      * @param      srcPos   starting position in the source array.
 554      * @param      dest     the destination array.
 555      * @param      destPos  starting position in the destination data.
 556      * @param      length   the number of array elements to be copied.
 557      * @throws     IndexOutOfBoundsException  if copying would cause
 558      *             access of data outside array bounds.
 559      * @throws     ArrayStoreException  if an element in the {@code src}
 560      *             array could not be stored into the {@code dest} array
 561      *             because of a type mismatch.
 562      * @throws     NullPointerException if either {@code src} or
 563      *             {@code dest} is {@code null}.
 564      */
 565     @HotSpotIntrinsicCandidate
 566     public static native void arraycopy(Object src,  int  srcPos,
 567                                         Object dest, int destPos,
 568                                         int length);
 569 
 570     /**
 571      * Returns the same hash code for the given object as
 572      * would be returned by the default method hashCode(),
 573      * whether or not the given object's class overrides
 574      * hashCode().
 575      * The hash code for the null reference is zero.
 576      *
 577      * @param x object for which the hashCode is to be calculated
 578      * @return  the hashCode
 579      * @since   1.1
 580      * @see Object#hashCode
 581      * @see java.util.Objects#hashCode(Object)
 582      */
 583     @HotSpotIntrinsicCandidate
 584     public static native int identityHashCode(Object x);
 585 
 586     /**
 587      * System properties. The following properties are guaranteed to be defined:
 588      * <dl>
 589      * <dt>java.version         <dd>Java version number
 590      * <dt>java.version.date    <dd>Java version date
 591      * <dt>java.vendor          <dd>Java vendor specific string
 592      * <dt>java.vendor.url      <dd>Java vendor URL
 593      * <dt>java.vendor.version  <dd>Java vendor version
 594      * <dt>java.home            <dd>Java installation directory
 595      * <dt>java.class.version   <dd>Java class version number
 596      * <dt>java.class.path      <dd>Java classpath
 597      * <dt>os.name              <dd>Operating System Name
 598      * <dt>os.arch              <dd>Operating System Architecture
 599      * <dt>os.version           <dd>Operating System Version
 600      * <dt>file.separator       <dd>File separator ("/" on Unix)
 601      * <dt>path.separator       <dd>Path separator (":" on Unix)
 602      * <dt>line.separator       <dd>Line separator ("\n" on Unix)
 603      * <dt>user.name            <dd>User account name
 604      * <dt>user.home            <dd>User home directory
 605      * <dt>user.dir             <dd>User's current working directory
 606      * </dl>
 607      */
 608 
 609     private static Properties props;
 610 
 611     /**
 612      * Determines the current system properties.
 613      *
 614      * First, if there is a security manager, its
 615      * {@code checkPropertiesAccess} method is called with no
 616      * arguments. This may result in a security exception.
 617      * <p>
 618      * The current set of system properties for use by the
 619      * {@link #getProperty(String)} method is returned as a
 620      * {@code Properties} object. If there is no current set of
 621      * system properties, a set of system properties is first created and
 622      * initialized. This set of system properties includes a value
 623      * for each of the following keys unless the description of the associated
 624      * value indicates that the value is optional.
 625      * <table class="striped" style="text-align:left">
 626      * <caption style="display:none">Shows property keys and associated values</caption>
 627      * <thead>
 628      * <tr><th scope="col">Key</th>
 629      *     <th scope="col">Description of Associated Value</th></tr>
 630      * </thead>
 631      * <tbody>
 632      * <tr><th scope="row">{@systemProperty java.version}</th>
 633      *     <td>Java Runtime Environment version, which may be interpreted
 634      *     as a {@link Runtime.Version}</td></tr>
 635      * <tr><th scope="row">{@systemProperty java.version.date}</th>
 636      *     <td>Java Runtime Environment version date, in ISO-8601 YYYY-MM-DD
 637      *     format, which may be interpreted as a {@link
 638      *     java.time.LocalDate}</td></tr>
 639      * <tr><th scope="row">{@systemProperty java.vendor}</th>
 640      *     <td>Java Runtime Environment vendor</td></tr>
 641      * <tr><th scope="row">{@systemProperty java.vendor.url}</th>
 642      *     <td>Java vendor URL</td></tr>
 643      * <tr><th scope="row">{@systemProperty java.vendor.version}</th>
 644      *     <td>Java vendor version <em>(optional)</em> </td></tr>
 645      * <tr><th scope="row">{@systemProperty java.home}</th>
 646      *     <td>Java installation directory</td></tr>
 647      * <tr><th scope="row">{@systemProperty java.vm.specification.version}</th>
 648      *     <td>Java Virtual Machine specification version, whose value is the
 649      *     {@linkplain Runtime.Version#feature feature} element of the
 650      *     {@linkplain Runtime#version() runtime version}</td></tr>
 651      * <tr><th scope="row">{@systemProperty java.vm.specification.vendor}</th>
 652      *     <td>Java Virtual Machine specification vendor</td></tr>
 653      * <tr><th scope="row">{@systemProperty java.vm.specification.name}</th>
 654      *     <td>Java Virtual Machine specification name</td></tr>
 655      * <tr><th scope="row">{@systemProperty java.vm.version}</th>
 656      *     <td>Java Virtual Machine implementation version which may be
 657      *     interpreted as a {@link Runtime.Version}</td></tr>
 658      * <tr><th scope="row">{@systemProperty java.vm.vendor}</th>
 659      *     <td>Java Virtual Machine implementation vendor</td></tr>
 660      * <tr><th scope="row">{@systemProperty java.vm.name}</th>
 661      *     <td>Java Virtual Machine implementation name</td></tr>
 662      * <tr><th scope="row">{@systemProperty java.specification.version}</th>
 663      *     <td>Java Runtime Environment specification version, whose value is
 664      *     the {@linkplain Runtime.Version#feature feature} element of the
 665      *     {@linkplain Runtime#version() runtime version}</td></tr>
 666      * <tr><th scope="row">{@systemProperty java.specification.vendor}</th>
 667      *     <td>Java Runtime Environment specification  vendor</td></tr>
 668      * <tr><th scope="row">{@systemProperty java.specification.name}</th>
 669      *     <td>Java Runtime Environment specification  name</td></tr>
 670      * <tr><th scope="row">{@systemProperty java.class.version}</th>
 671      *     <td>Java class format version number</td></tr>
 672      * <tr><th scope="row">{@systemProperty java.class.path}</th>
 673      *     <td>Java class path  (refer to
 674      *        {@link ClassLoader#getSystemClassLoader()} for details)</td></tr>
 675      * <tr><th scope="row">{@systemProperty java.library.path}</th>
 676      *     <td>List of paths to search when loading libraries</td></tr>
 677      * <tr><th scope="row">{@systemProperty java.io.tmpdir}</th>
 678      *     <td>Default temp file path</td></tr>
 679      * <tr><th scope="row">{@systemProperty java.compiler}</th>
 680      *     <td>Name of JIT compiler to use</td></tr>
 681      * <tr><th scope="row">{@systemProperty os.name}</th>
 682      *     <td>Operating system name</td></tr>
 683      * <tr><th scope="row">{@systemProperty os.arch}</th>
 684      *     <td>Operating system architecture</td></tr>
 685      * <tr><th scope="row">{@systemProperty os.version}</th>
 686      *     <td>Operating system version</td></tr>
 687      * <tr><th scope="row">{@systemProperty file.separator}</th>
 688      *     <td>File separator ("/" on UNIX)</td></tr>
 689      * <tr><th scope="row">{@systemProperty path.separator}</th>
 690      *     <td>Path separator (":" on UNIX)</td></tr>
 691      * <tr><th scope="row">{@systemProperty line.separator}</th>
 692      *     <td>Line separator ("\n" on UNIX)</td></tr>
 693      * <tr><th scope="row">{@systemProperty user.name}</th>
 694      *     <td>User's account name</td></tr>
 695      * <tr><th scope="row">{@systemProperty user.home}</th>
 696      *     <td>User's home directory</td></tr>
 697      * <tr><th scope="row">{@systemProperty user.dir}</th>
 698      *     <td>User's current working directory</td></tr>
 699      * </tbody>
 700      * </table>
 701      * <p>
 702      * Multiple paths in a system property value are separated by the path
 703      * separator character of the platform.
 704      * <p>
 705      * Note that even if the security manager does not permit the
 706      * {@code getProperties} operation, it may choose to permit the
 707      * {@link #getProperty(String)} operation.
 708      *
 709      * @apiNote
 710      * <strong>Changing a standard system property may have unpredictable results
 711      * unless otherwise specified.</strong>
 712      * Property values may be cached during initialization or on first use.
 713      * Setting a standard property after initialization using {@link #getProperties()},
 714      * {@link #setProperties(Properties)}, {@link #setProperty(String, String)}, or
 715      * {@link #clearProperty(String)} may not have the desired effect.
 716      *
 717      * @implNote
 718      * In addition to the standard system properties, the system
 719      * properties may include the following keys:
 720      * <table class="striped">
 721      * <caption style="display:none">Shows property keys and associated values</caption>
 722      * <thead>
 723      * <tr><th scope="col">Key</th>
 724      *     <th scope="col">Description of Associated Value</th></tr>
 725      * </thead>
 726      * <tbody>
 727      * <tr><th scope="row">{@systemProperty jdk.module.path}</th>
 728      *     <td>The application module path</td></tr>
 729      * <tr><th scope="row">{@systemProperty jdk.module.upgrade.path}</th>
 730      *     <td>The upgrade module path</td></tr>
 731      * <tr><th scope="row">{@systemProperty jdk.module.main}</th>
 732      *     <td>The module name of the initial/main module</td></tr>
 733      * <tr><th scope="row">{@systemProperty jdk.module.main.class}</th>
 734      *     <td>The main class name of the initial module</td></tr>
 735      * </tbody>
 736      * </table>
 737      *
 738      * @return     the system properties
 739      * @throws     SecurityException  if a security manager exists and its
 740      *             {@code checkPropertiesAccess} method doesn't allow access
 741      *             to the system properties.
 742      * @see        #setProperties
 743      * @see        java.lang.SecurityException
 744      * @see        java.lang.SecurityManager#checkPropertiesAccess()
 745      * @see        java.util.Properties
 746      */
 747     public static Properties getProperties() {
 748         SecurityManager sm = getSecurityManager();
 749         if (sm != null) {
 750             sm.checkPropertiesAccess();
 751         }
 752 
 753         return props;
 754     }
 755 
 756     /**
 757      * Returns the system-dependent line separator string.  It always
 758      * returns the same value - the initial value of the {@linkplain
 759      * #getProperty(String) system property} {@code line.separator}.
 760      *
 761      * <p>On UNIX systems, it returns {@code "\n"}; on Microsoft
 762      * Windows systems it returns {@code "\r\n"}.
 763      *
 764      * @return the system-dependent line separator string
 765      * @since 1.7
 766      */
 767     public static String lineSeparator() {
 768         return lineSeparator;
 769     }
 770 
 771     private static String lineSeparator;
 772 
 773     /**
 774      * Sets the system properties to the {@code Properties} argument.
 775      *
 776      * First, if there is a security manager, its
 777      * {@code checkPropertiesAccess} method is called with no
 778      * arguments. This may result in a security exception.
 779      * <p>
 780      * The argument becomes the current set of system properties for use
 781      * by the {@link #getProperty(String)} method. If the argument is
 782      * {@code null}, then the current set of system properties is
 783      * forgotten.
 784      *
 785      * @apiNote
 786      * <strong>Changing a standard system property may have unpredictable results
 787      * unless otherwise specified</strong>.
 788      * See {@linkplain #getProperties getProperties} for details.
 789      *
 790      * @param      props   the new system properties.
 791      * @throws     SecurityException  if a security manager exists and its
 792      *             {@code checkPropertiesAccess} method doesn't allow access
 793      *             to the system properties.
 794      * @see        #getProperties
 795      * @see        java.util.Properties
 796      * @see        java.lang.SecurityException
 797      * @see        java.lang.SecurityManager#checkPropertiesAccess()
 798      */
 799     public static void setProperties(Properties props) {
 800         SecurityManager sm = getSecurityManager();
 801         if (sm != null) {
 802             sm.checkPropertiesAccess();
 803         }
 804 
 805         if (props == null) {
 806             Map<String, String> tempProps = SystemProps.initProperties();
 807             VersionProps.init(tempProps);
 808             props = createProperties(tempProps);
 809         }
 810         System.props = props;
 811     }
 812 
 813     /**
 814      * Gets the system property indicated by the specified key.
 815      *
 816      * First, if there is a security manager, its
 817      * {@code checkPropertyAccess} method is called with the key as
 818      * its argument. This may result in a SecurityException.
 819      * <p>
 820      * If there is no current set of system properties, a set of system
 821      * properties is first created and initialized in the same manner as
 822      * for the {@code getProperties} method.
 823      *
 824      * @apiNote
 825      * <strong>Changing a standard system property may have unpredictable results
 826      * unless otherwise specified</strong>.
 827      * See {@linkplain #getProperties getProperties} for details.
 828      *
 829      * @param      key   the name of the system property.
 830      * @return     the string value of the system property,
 831      *             or {@code null} if there is no property with that key.
 832      *
 833      * @throws     SecurityException  if a security manager exists and its
 834      *             {@code checkPropertyAccess} method doesn't allow
 835      *             access to the specified system property.
 836      * @throws     NullPointerException if {@code key} is {@code null}.
 837      * @throws     IllegalArgumentException if {@code key} is empty.
 838      * @see        #setProperty
 839      * @see        java.lang.SecurityException
 840      * @see        java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
 841      * @see        java.lang.System#getProperties()
 842      */
 843     public static String getProperty(String key) {
 844         checkKey(key);
 845         SecurityManager sm = getSecurityManager();
 846         if (sm != null) {
 847             sm.checkPropertyAccess(key);
 848         }
 849 
 850         return props.getProperty(key);
 851     }
 852 
 853     /**
 854      * Gets the system property indicated by the specified key.
 855      *
 856      * First, if there is a security manager, its
 857      * {@code checkPropertyAccess} method is called with the
 858      * {@code key} as its argument.
 859      * <p>
 860      * If there is no current set of system properties, a set of system
 861      * properties is first created and initialized in the same manner as
 862      * for the {@code getProperties} method.
 863      *
 864      * @param      key   the name of the system property.
 865      * @param      def   a default value.
 866      * @return     the string value of the system property,
 867      *             or the default value if there is no property with that key.
 868      *
 869      * @throws     SecurityException  if a security manager exists and its
 870      *             {@code checkPropertyAccess} method doesn't allow
 871      *             access to the specified system property.
 872      * @throws     NullPointerException if {@code key} is {@code null}.
 873      * @throws     IllegalArgumentException if {@code key} is empty.
 874      * @see        #setProperty
 875      * @see        java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
 876      * @see        java.lang.System#getProperties()
 877      */
 878     public static String getProperty(String key, String def) {
 879         checkKey(key);
 880         SecurityManager sm = getSecurityManager();
 881         if (sm != null) {
 882             sm.checkPropertyAccess(key);
 883         }
 884 
 885         return props.getProperty(key, def);
 886     }
 887 
 888     /**
 889      * Sets the system property indicated by the specified key.
 890      *
 891      * First, if a security manager exists, its
 892      * {@code SecurityManager.checkPermission} method
 893      * is called with a {@code PropertyPermission(key, "write")}
 894      * permission. This may result in a SecurityException being thrown.
 895      * If no exception is thrown, the specified property is set to the given
 896      * value.
 897      *
 898      * @apiNote
 899      * <strong>Changing a standard system property may have unpredictable results
 900      * unless otherwise specified</strong>.
 901      * See {@linkplain #getProperties getProperties} for details.
 902      *
 903      * @param      key   the name of the system property.
 904      * @param      value the value of the system property.
 905      * @return     the previous value of the system property,
 906      *             or {@code null} if it did not have one.
 907      *
 908      * @throws     SecurityException  if a security manager exists and its
 909      *             {@code checkPermission} method doesn't allow
 910      *             setting of the specified property.
 911      * @throws     NullPointerException if {@code key} or
 912      *             {@code value} is {@code null}.
 913      * @throws     IllegalArgumentException if {@code key} is empty.
 914      * @see        #getProperty
 915      * @see        java.lang.System#getProperty(java.lang.String)
 916      * @see        java.lang.System#getProperty(java.lang.String, java.lang.String)
 917      * @see        java.util.PropertyPermission
 918      * @see        SecurityManager#checkPermission
 919      * @since      1.2
 920      */
 921     public static String setProperty(String key, String value) {
 922         checkKey(key);
 923         SecurityManager sm = getSecurityManager();
 924         if (sm != null) {
 925             sm.checkPermission(new PropertyPermission(key,
 926                 SecurityConstants.PROPERTY_WRITE_ACTION));
 927         }
 928 
 929         return (String) props.setProperty(key, value);
 930     }
 931 
 932     /**
 933      * Removes the system property indicated by the specified key.
 934      *
 935      * First, if a security manager exists, its
 936      * {@code SecurityManager.checkPermission} method
 937      * is called with a {@code PropertyPermission(key, "write")}
 938      * permission. This may result in a SecurityException being thrown.
 939      * If no exception is thrown, the specified property is removed.
 940      *
 941      * @apiNote
 942      * <strong>Changing a standard system property may have unpredictable results
 943      * unless otherwise specified</strong>.
 944      * See {@linkplain #getProperties getProperties} method for details.
 945      *
 946      * @param      key   the name of the system property to be removed.
 947      * @return     the previous string value of the system property,
 948      *             or {@code null} if there was no property with that key.
 949      *
 950      * @throws     SecurityException  if a security manager exists and its
 951      *             {@code checkPropertyAccess} method doesn't allow
 952      *              access to the specified system property.
 953      * @throws     NullPointerException if {@code key} is {@code null}.
 954      * @throws     IllegalArgumentException if {@code key} is empty.
 955      * @see        #getProperty
 956      * @see        #setProperty
 957      * @see        java.util.Properties
 958      * @see        java.lang.SecurityException
 959      * @see        java.lang.SecurityManager#checkPropertiesAccess()
 960      * @since 1.5
 961      */
 962     public static String clearProperty(String key) {
 963         checkKey(key);
 964         SecurityManager sm = getSecurityManager();
 965         if (sm != null) {
 966             sm.checkPermission(new PropertyPermission(key, "write"));
 967         }
 968 
 969         return (String) props.remove(key);
 970     }
 971 
 972     private static void checkKey(String key) {
 973         if (key == null) {
 974             throw new NullPointerException("key can't be null");
 975         }
 976         if (key.isEmpty()) {
 977             throw new IllegalArgumentException("key can't be empty");
 978         }
 979     }
 980 
 981     /**
 982      * Gets the value of the specified environment variable. An
 983      * environment variable is a system-dependent external named
 984      * value.
 985      *
 986      * <p>If a security manager exists, its
 987      * {@link SecurityManager#checkPermission checkPermission}
 988      * method is called with a
 989      * {@link RuntimePermission RuntimePermission("getenv."+name)}
 990      * permission.  This may result in a {@link SecurityException}
 991      * being thrown.  If no exception is thrown the value of the
 992      * variable {@code name} is returned.
 993      *
 994      * <p><a id="EnvironmentVSSystemProperties"><i>System
 995      * properties</i> and <i>environment variables</i></a> are both
 996      * conceptually mappings between names and values.  Both
 997      * mechanisms can be used to pass user-defined information to a
 998      * Java process.  Environment variables have a more global effect,
 999      * because they are visible to all descendants of the process
1000      * which defines them, not just the immediate Java subprocess.
1001      * They can have subtly different semantics, such as case
1002      * insensitivity, on different operating systems.  For these
1003      * reasons, environment variables are more likely to have
1004      * unintended side effects.  It is best to use system properties
1005      * where possible.  Environment variables should be used when a
1006      * global effect is desired, or when an external system interface
1007      * requires an environment variable (such as {@code PATH}).
1008      *
1009      * <p>On UNIX systems the alphabetic case of {@code name} is
1010      * typically significant, while on Microsoft Windows systems it is
1011      * typically not.  For example, the expression
1012      * {@code System.getenv("FOO").equals(System.getenv("foo"))}
1013      * is likely to be true on Microsoft Windows.
1014      *
1015      * @param  name the name of the environment variable
1016      * @return the string value of the variable, or {@code null}
1017      *         if the variable is not defined in the system environment
1018      * @throws NullPointerException if {@code name} is {@code null}
1019      * @throws SecurityException
1020      *         if a security manager exists and its
1021      *         {@link SecurityManager#checkPermission checkPermission}
1022      *         method doesn't allow access to the environment variable
1023      *         {@code name}
1024      * @see    #getenv()
1025      * @see    ProcessBuilder#environment()
1026      */
1027     public static String getenv(String name) {
1028         SecurityManager sm = getSecurityManager();
1029         if (sm != null) {
1030             sm.checkPermission(new RuntimePermission("getenv."+name));
1031         }
1032 
1033         return ProcessEnvironment.getenv(name);
1034     }
1035 
1036 
1037     /**
1038      * Returns an unmodifiable string map view of the current system environment.
1039      * The environment is a system-dependent mapping from names to
1040      * values which is passed from parent to child processes.
1041      *
1042      * <p>If the system does not support environment variables, an
1043      * empty map is returned.
1044      *
1045      * <p>The returned map will never contain null keys or values.
1046      * Attempting to query the presence of a null key or value will
1047      * throw a {@link NullPointerException}.  Attempting to query
1048      * the presence of a key or value which is not of type
1049      * {@link String} will throw a {@link ClassCastException}.
1050      *
1051      * <p>The returned map and its collection views may not obey the
1052      * general contract of the {@link Object#equals} and
1053      * {@link Object#hashCode} methods.
1054      *
1055      * <p>The returned map is typically case-sensitive on all platforms.
1056      *
1057      * <p>If a security manager exists, its
1058      * {@link SecurityManager#checkPermission checkPermission}
1059      * method is called with a
1060      * {@link RuntimePermission RuntimePermission("getenv.*")} permission.
1061      * This may result in a {@link SecurityException} being thrown.
1062      *
1063      * <p>When passing information to a Java subprocess,
1064      * <a href=#EnvironmentVSSystemProperties>system properties</a>
1065      * are generally preferred over environment variables.
1066      *
1067      * @return the environment as a map of variable names to values
1068      * @throws SecurityException
1069      *         if a security manager exists and its
1070      *         {@link SecurityManager#checkPermission checkPermission}
1071      *         method doesn't allow access to the process environment
1072      * @see    #getenv(String)
1073      * @see    ProcessBuilder#environment()
1074      * @since  1.5
1075      */
1076     public static java.util.Map<String,String> getenv() {
1077         SecurityManager sm = getSecurityManager();
1078         if (sm != null) {
1079             sm.checkPermission(new RuntimePermission("getenv.*"));
1080         }
1081 
1082         return ProcessEnvironment.getenv();
1083     }
1084 
1085     /**
1086      * {@code System.Logger} instances log messages that will be
1087      * routed to the underlying logging framework the {@link System.LoggerFinder
1088      * LoggerFinder} uses.
1089      *
1090      * {@code System.Logger} instances are typically obtained from
1091      * the {@link java.lang.System System} class, by calling
1092      * {@link java.lang.System#getLogger(java.lang.String) System.getLogger(loggerName)}
1093      * or {@link java.lang.System#getLogger(java.lang.String, java.util.ResourceBundle)
1094      * System.getLogger(loggerName, bundle)}.
1095      *
1096      * @see java.lang.System#getLogger(java.lang.String)
1097      * @see java.lang.System#getLogger(java.lang.String, java.util.ResourceBundle)
1098      * @see java.lang.System.LoggerFinder
1099      *
1100      * @since 9
1101      */
1102     public interface Logger {
1103 
1104         /**
1105          * System {@linkplain Logger loggers} levels.
1106          *
1107          * A level has a {@linkplain #getName() name} and {@linkplain
1108          * #getSeverity() severity}.
1109          * Level values are {@link #ALL}, {@link #TRACE}, {@link #DEBUG},
1110          * {@link #INFO}, {@link #WARNING}, {@link #ERROR}, {@link #OFF},
1111          * by order of increasing severity.
1112          * <br>
1113          * {@link #ALL} and {@link #OFF}
1114          * are simple markers with severities mapped respectively to
1115          * {@link java.lang.Integer#MIN_VALUE Integer.MIN_VALUE} and
1116          * {@link java.lang.Integer#MAX_VALUE Integer.MAX_VALUE}.
1117          * <p>
1118          * <b>Severity values and Mapping to {@code java.util.logging.Level}.</b>
1119          * <p>
1120          * {@linkplain System.Logger.Level System logger levels} are mapped to
1121          * {@linkplain java.util.logging.Level  java.util.logging levels}
1122          * of corresponding severity.
1123          * <br>The mapping is as follows:
1124          * <br><br>
1125          * <table class="striped">
1126          * <caption>System.Logger Severity Level Mapping</caption>
1127          * <thead>
1128          * <tr><th scope="col">System.Logger Levels</th>
1129          *     <th scope="col">java.util.logging Levels</th>
1130          * </thead>
1131          * <tbody>
1132          * <tr><th scope="row">{@link Logger.Level#ALL ALL}</th>
1133          *     <td>{@link java.util.logging.Level#ALL ALL}</td>
1134          * <tr><th scope="row">{@link Logger.Level#TRACE TRACE}</th>
1135          *     <td>{@link java.util.logging.Level#FINER FINER}</td>
1136          * <tr><th scope="row">{@link Logger.Level#DEBUG DEBUG}</th>
1137          *     <td>{@link java.util.logging.Level#FINE FINE}</td>
1138          * <tr><th scope="row">{@link Logger.Level#INFO INFO}</th>
1139          *     <td>{@link java.util.logging.Level#INFO INFO}</td>
1140          * <tr><th scope="row">{@link Logger.Level#WARNING WARNING}</th>
1141          *     <td>{@link java.util.logging.Level#WARNING WARNING}</td>
1142          * <tr><th scope="row">{@link Logger.Level#ERROR ERROR}</th>
1143          *     <td>{@link java.util.logging.Level#SEVERE SEVERE}</td>
1144          * <tr><th scope="row">{@link Logger.Level#OFF OFF}</th>
1145          *     <td>{@link java.util.logging.Level#OFF OFF}</td>
1146          * </tbody>
1147          * </table>
1148          *
1149          * @since 9
1150          *
1151          * @see java.lang.System.LoggerFinder
1152          * @see java.lang.System.Logger
1153          */
1154         public enum Level {
1155 
1156             // for convenience, we're reusing java.util.logging.Level int values
1157             // the mapping logic in sun.util.logging.PlatformLogger depends
1158             // on this.
1159             /**
1160              * A marker to indicate that all levels are enabled.
1161              * This level {@linkplain #getSeverity() severity} is
1162              * {@link Integer#MIN_VALUE}.
1163              */
1164             ALL(Integer.MIN_VALUE),  // typically mapped to/from j.u.l.Level.ALL
1165             /**
1166              * {@code TRACE} level: usually used to log diagnostic information.
1167              * This level {@linkplain #getSeverity() severity} is
1168              * {@code 400}.
1169              */
1170             TRACE(400),   // typically mapped to/from j.u.l.Level.FINER
1171             /**
1172              * {@code DEBUG} level: usually used to log debug information traces.
1173              * This level {@linkplain #getSeverity() severity} is
1174              * {@code 500}.
1175              */
1176             DEBUG(500),   // typically mapped to/from j.u.l.Level.FINEST/FINE/CONFIG
1177             /**
1178              * {@code INFO} level: usually used to log information messages.
1179              * This level {@linkplain #getSeverity() severity} is
1180              * {@code 800}.
1181              */
1182             INFO(800),    // typically mapped to/from j.u.l.Level.INFO
1183             /**
1184              * {@code WARNING} level: usually used to log warning messages.
1185              * This level {@linkplain #getSeverity() severity} is
1186              * {@code 900}.
1187              */
1188             WARNING(900), // typically mapped to/from j.u.l.Level.WARNING
1189             /**
1190              * {@code ERROR} level: usually used to log error messages.
1191              * This level {@linkplain #getSeverity() severity} is
1192              * {@code 1000}.
1193              */
1194             ERROR(1000),  // typically mapped to/from j.u.l.Level.SEVERE
1195             /**
1196              * A marker to indicate that all levels are disabled.
1197              * This level {@linkplain #getSeverity() severity} is
1198              * {@link Integer#MAX_VALUE}.
1199              */
1200             OFF(Integer.MAX_VALUE);  // typically mapped to/from j.u.l.Level.OFF
1201 
1202             private final int severity;
1203 
1204             private Level(int severity) {
1205                 this.severity = severity;
1206             }
1207 
1208             /**
1209              * Returns the name of this level.
1210              * @return this level {@linkplain #name()}.
1211              */
1212             public final String getName() {
1213                 return name();
1214             }
1215 
1216             /**
1217              * Returns the severity of this level.
1218              * A higher severity means a more severe condition.
1219              * @return this level severity.
1220              */
1221             public final int getSeverity() {
1222                 return severity;
1223             }
1224         }
1225 
1226         /**
1227          * Returns the name of this logger.
1228          *
1229          * @return the logger name.
1230          */
1231         public String getName();
1232 
1233         /**
1234          * Checks if a message of the given level would be logged by
1235          * this logger.
1236          *
1237          * @param level the log message level.
1238          * @return {@code true} if the given log message level is currently
1239          *         being logged.
1240          *
1241          * @throws NullPointerException if {@code level} is {@code null}.
1242          */
1243         public boolean isLoggable(Level level);
1244 
1245         /**
1246          * Logs a message.
1247          *
1248          * @implSpec The default implementation for this method calls
1249          * {@code this.log(level, (ResourceBundle)null, msg, (Object[])null);}
1250          *
1251          * @param level the log message level.
1252          * @param msg the string message (or a key in the message catalog, if
1253          * this logger is a {@link
1254          * LoggerFinder#getLocalizedLogger(java.lang.String,
1255          * java.util.ResourceBundle, java.lang.Module) localized logger});
1256          * can be {@code null}.
1257          *
1258          * @throws NullPointerException if {@code level} is {@code null}.
1259          */
1260         public default void log(Level level, String msg) {
1261             log(level, (ResourceBundle) null, msg, (Object[]) null);
1262         }
1263 
1264         /**
1265          * Logs a lazily supplied message.
1266          *
1267          * If the logger is currently enabled for the given log message level
1268          * then a message is logged that is the result produced by the
1269          * given supplier function.  Otherwise, the supplier is not operated on.
1270          *
1271          * @implSpec When logging is enabled for the given level, the default
1272          * implementation for this method calls
1273          * {@code this.log(level, (ResourceBundle)null, msgSupplier.get(), (Object[])null);}
1274          *
1275          * @param level the log message level.
1276          * @param msgSupplier a supplier function that produces a message.
1277          *
1278          * @throws NullPointerException if {@code level} is {@code null},
1279          *         or {@code msgSupplier} is {@code null}.
1280          */
1281         public default void log(Level level, Supplier<String> msgSupplier) {
1282             Objects.requireNonNull(msgSupplier);
1283             if (isLoggable(Objects.requireNonNull(level))) {
1284                 log(level, (ResourceBundle) null, msgSupplier.get(), (Object[]) null);
1285             }
1286         }
1287 
1288         /**
1289          * Logs a message produced from the given object.
1290          *
1291          * If the logger is currently enabled for the given log message level then
1292          * a message is logged that, by default, is the result produced from
1293          * calling  toString on the given object.
1294          * Otherwise, the object is not operated on.
1295          *
1296          * @implSpec When logging is enabled for the given level, the default
1297          * implementation for this method calls
1298          * {@code this.log(level, (ResourceBundle)null, obj.toString(), (Object[])null);}
1299          *
1300          * @param level the log message level.
1301          * @param obj the object to log.
1302          *
1303          * @throws NullPointerException if {@code level} is {@code null}, or
1304          *         {@code obj} is {@code null}.
1305          */
1306         public default void log(Level level, Object obj) {
1307             Objects.requireNonNull(obj);
1308             if (isLoggable(Objects.requireNonNull(level))) {
1309                 this.log(level, (ResourceBundle) null, obj.toString(), (Object[]) null);
1310             }
1311         }
1312 
1313         /**
1314          * Logs a message associated with a given throwable.
1315          *
1316          * @implSpec The default implementation for this method calls
1317          * {@code this.log(level, (ResourceBundle)null, msg, thrown);}
1318          *
1319          * @param level the log message level.
1320          * @param msg the string message (or a key in the message catalog, if
1321          * this logger is a {@link
1322          * LoggerFinder#getLocalizedLogger(java.lang.String,
1323          * java.util.ResourceBundle, java.lang.Module) localized logger});
1324          * can be {@code null}.
1325          * @param thrown a {@code Throwable} associated with the log message;
1326          *        can be {@code null}.
1327          *
1328          * @throws NullPointerException if {@code level} is {@code null}.
1329          */
1330         public default void log(Level level, String msg, Throwable thrown) {
1331             this.log(level, null, msg, thrown);
1332         }
1333 
1334         /**
1335          * Logs a lazily supplied message associated with a given throwable.
1336          *
1337          * If the logger is currently enabled for the given log message level
1338          * then a message is logged that is the result produced by the
1339          * given supplier function.  Otherwise, the supplier is not operated on.
1340          *
1341          * @implSpec When logging is enabled for the given level, the default
1342          * implementation for this method calls
1343          * {@code this.log(level, (ResourceBundle)null, msgSupplier.get(), thrown);}
1344          *
1345          * @param level one of the log message level identifiers.
1346          * @param msgSupplier a supplier function that produces a message.
1347          * @param thrown a {@code Throwable} associated with log message;
1348          *               can be {@code null}.
1349          *
1350          * @throws NullPointerException if {@code level} is {@code null}, or
1351          *                               {@code msgSupplier} is {@code null}.
1352          */
1353         public default void log(Level level, Supplier<String> msgSupplier,
1354                 Throwable thrown) {
1355             Objects.requireNonNull(msgSupplier);
1356             if (isLoggable(Objects.requireNonNull(level))) {
1357                 this.log(level, null, msgSupplier.get(), thrown);
1358             }
1359         }
1360 
1361         /**
1362          * Logs a message with an optional list of parameters.
1363          *
1364          * @implSpec The default implementation for this method calls
1365          * {@code this.log(level, (ResourceBundle)null, format, params);}
1366          *
1367          * @param level one of the log message level identifiers.
1368          * @param format the string message format in {@link
1369          * java.text.MessageFormat} format, (or a key in the message
1370          * catalog, if this logger is a {@link
1371          * LoggerFinder#getLocalizedLogger(java.lang.String,
1372          * java.util.ResourceBundle, java.lang.Module) localized logger});
1373          * can be {@code null}.
1374          * @param params an optional list of parameters to the message (may be
1375          * none).
1376          *
1377          * @throws NullPointerException if {@code level} is {@code null}.
1378          */
1379         public default void log(Level level, String format, Object... params) {
1380             this.log(level, null, format, params);
1381         }
1382 
1383         /**
1384          * Logs a localized message associated with a given throwable.
1385          *
1386          * If the given resource bundle is non-{@code null},  the {@code msg}
1387          * string is localized using the given resource bundle.
1388          * Otherwise the {@code msg} string is not localized.
1389          *
1390          * @param level the log message level.
1391          * @param bundle a resource bundle to localize {@code msg}; can be
1392          * {@code null}.
1393          * @param msg the string message (or a key in the message catalog,
1394          *            if {@code bundle} is not {@code null}); can be {@code null}.
1395          * @param thrown a {@code Throwable} associated with the log message;
1396          *        can be {@code null}.
1397          *
1398          * @throws NullPointerException if {@code level} is {@code null}.
1399          */
1400         public void log(Level level, ResourceBundle bundle, String msg,
1401                 Throwable thrown);
1402 
1403         /**
1404          * Logs a message with resource bundle and an optional list of
1405          * parameters.
1406          *
1407          * If the given resource bundle is non-{@code null},  the {@code format}
1408          * string is localized using the given resource bundle.
1409          * Otherwise the {@code format} string is not localized.
1410          *
1411          * @param level the log message level.
1412          * @param bundle a resource bundle to localize {@code format}; can be
1413          * {@code null}.
1414          * @param format the string message format in {@link
1415          * java.text.MessageFormat} format, (or a key in the message
1416          * catalog if {@code bundle} is not {@code null}); can be {@code null}.
1417          * @param params an optional list of parameters to the message (may be
1418          * none).
1419          *
1420          * @throws NullPointerException if {@code level} is {@code null}.
1421          */
1422         public void log(Level level, ResourceBundle bundle, String format,
1423                 Object... params);
1424     }
1425 
1426     /**
1427      * The {@code LoggerFinder} service is responsible for creating, managing,
1428      * and configuring loggers to the underlying framework it uses.
1429      *
1430      * A logger finder is a concrete implementation of this class that has a
1431      * zero-argument constructor and implements the abstract methods defined
1432      * by this class.
1433      * The loggers returned from a logger finder are capable of routing log
1434      * messages to the logging backend this provider supports.
1435      * A given invocation of the Java Runtime maintains a single
1436      * system-wide LoggerFinder instance that is loaded as follows:
1437      * <ul>
1438      *    <li>First it finds any custom {@code LoggerFinder} provider
1439      *        using the {@link java.util.ServiceLoader} facility with the
1440      *        {@linkplain ClassLoader#getSystemClassLoader() system class
1441      *        loader}.</li>
1442      *    <li>If no {@code LoggerFinder} provider is found, the system default
1443      *        {@code LoggerFinder} implementation will be used.</li>
1444      * </ul>
1445      * <p>
1446      * An application can replace the logging backend
1447      * <i>even when the java.logging module is present</i>, by simply providing
1448      * and declaring an implementation of the {@link LoggerFinder} service.
1449      * <p>
1450      * <b>Default Implementation</b>
1451      * <p>
1452      * The system default {@code LoggerFinder} implementation uses
1453      * {@code java.util.logging} as the backend framework when the
1454      * {@code java.logging} module is present.
1455      * It returns a {@linkplain System.Logger logger} instance
1456      * that will route log messages to a {@link java.util.logging.Logger
1457      * java.util.logging.Logger}. Otherwise, if {@code java.logging} is not
1458      * present, the default implementation will return a simple logger
1459      * instance that will route log messages of {@code INFO} level and above to
1460      * the console ({@code System.err}).
1461      * <p>
1462      * <b>Logging Configuration</b>
1463      * <p>
1464      * {@linkplain Logger Logger} instances obtained from the
1465      * {@code LoggerFinder} factory methods are not directly configurable by
1466      * the application. Configuration is the responsibility of the underlying
1467      * logging backend, and usually requires using APIs specific to that backend.
1468      * <p>For the default {@code LoggerFinder} implementation
1469      * using {@code java.util.logging} as its backend, refer to
1470      * {@link java.util.logging java.util.logging} for logging configuration.
1471      * For the default {@code LoggerFinder} implementation returning simple loggers
1472      * when the {@code java.logging} module is absent, the configuration
1473      * is implementation dependent.
1474      * <p>
1475      * Usually an application that uses a logging framework will log messages
1476      * through a logger facade defined (or supported) by that framework.
1477      * Applications that wish to use an external framework should log
1478      * through the facade associated with that framework.
1479      * <p>
1480      * A system class that needs to log messages will typically obtain
1481      * a {@link System.Logger} instance to route messages to the logging
1482      * framework selected by the application.
1483      * <p>
1484      * Libraries and classes that only need loggers to produce log messages
1485      * should not attempt to configure loggers by themselves, as that
1486      * would make them dependent from a specific implementation of the
1487      * {@code LoggerFinder} service.
1488      * <p>
1489      * In addition, when a security manager is present, loggers provided to
1490      * system classes should not be directly configurable through the logging
1491      * backend without requiring permissions.
1492      * <br>
1493      * It is the responsibility of the provider of
1494      * the concrete {@code LoggerFinder} implementation to ensure that
1495      * these loggers are not configured by untrusted code without proper
1496      * permission checks, as configuration performed on such loggers usually
1497      * affects all applications in the same Java Runtime.
1498      * <p>
1499      * <b>Message Levels and Mapping to backend levels</b>
1500      * <p>
1501      * A logger finder is responsible for mapping from a {@code
1502      * System.Logger.Level} to a level supported by the logging backend it uses.
1503      * <br>The default LoggerFinder using {@code java.util.logging} as the backend
1504      * maps {@code System.Logger} levels to
1505      * {@linkplain java.util.logging.Level java.util.logging} levels
1506      * of corresponding severity - as described in {@link Logger.Level
1507      * Logger.Level}.
1508      *
1509      * @see java.lang.System
1510      * @see java.lang.System.Logger
1511      *
1512      * @since 9
1513      */
1514     public static abstract class LoggerFinder {
1515         /**
1516          * The {@code RuntimePermission("loggerFinder")} is
1517          * necessary to subclass and instantiate the {@code LoggerFinder} class,
1518          * as well as to obtain loggers from an instance of that class.
1519          */
1520         static final RuntimePermission LOGGERFINDER_PERMISSION =
1521                 new RuntimePermission("loggerFinder");
1522 
1523         /**
1524          * Creates a new instance of {@code LoggerFinder}.
1525          *
1526          * @implNote It is recommended that a {@code LoggerFinder} service
1527          *   implementation does not perform any heavy initialization in its
1528          *   constructor, in order to avoid possible risks of deadlock or class
1529          *   loading cycles during the instantiation of the service provider.
1530          *
1531          * @throws SecurityException if a security manager is present and its
1532          *         {@code checkPermission} method doesn't allow the
1533          *         {@code RuntimePermission("loggerFinder")}.
1534          */
1535         protected LoggerFinder() {
1536             this(checkPermission());
1537         }
1538 
1539         private LoggerFinder(Void unused) {
1540             // nothing to do.
1541         }
1542 
1543         private static Void checkPermission() {
1544             final SecurityManager sm = System.getSecurityManager();
1545             if (sm != null) {
1546                 sm.checkPermission(LOGGERFINDER_PERMISSION);
1547             }
1548             return null;
1549         }
1550 
1551         /**
1552          * Returns an instance of {@link Logger Logger}
1553          * for the given {@code module}.
1554          *
1555          * @param name the name of the logger.
1556          * @param module the module for which the logger is being requested.
1557          *
1558          * @return a {@link Logger logger} suitable for use within the given
1559          *         module.
1560          * @throws NullPointerException if {@code name} is {@code null} or
1561          *        {@code module} is {@code null}.
1562          * @throws SecurityException if a security manager is present and its
1563          *         {@code checkPermission} method doesn't allow the
1564          *         {@code RuntimePermission("loggerFinder")}.
1565          */
1566         public abstract Logger getLogger(String name, Module module);
1567 
1568         /**
1569          * Returns a localizable instance of {@link Logger Logger}
1570          * for the given {@code module}.
1571          * The returned logger will use the provided resource bundle for
1572          * message localization.
1573          *
1574          * @implSpec By default, this method calls {@link
1575          * #getLogger(java.lang.String, java.lang.Module)
1576          * this.getLogger(name, module)} to obtain a logger, then wraps that
1577          * logger in a {@link Logger} instance where all methods that do not
1578          * take a {@link ResourceBundle} as parameter are redirected to one
1579          * which does - passing the given {@code bundle} for
1580          * localization. So for instance, a call to {@link
1581          * Logger#log(Logger.Level, String) Logger.log(Level.INFO, msg)}
1582          * will end up as a call to {@link
1583          * Logger#log(Logger.Level, ResourceBundle, String, Object...)
1584          * Logger.log(Level.INFO, bundle, msg, (Object[])null)} on the wrapped
1585          * logger instance.
1586          * Note however that by default, string messages returned by {@link
1587          * java.util.function.Supplier Supplier&lt;String&gt;} will not be
1588          * localized, as it is assumed that such strings are messages which are
1589          * already constructed, rather than keys in a resource bundle.
1590          * <p>
1591          * An implementation of {@code LoggerFinder} may override this method,
1592          * for example, when the underlying logging backend provides its own
1593          * mechanism for localizing log messages, then such a
1594          * {@code LoggerFinder} would be free to return a logger
1595          * that makes direct use of the mechanism provided by the backend.
1596          *
1597          * @param name    the name of the logger.
1598          * @param bundle  a resource bundle; can be {@code null}.
1599          * @param module  the module for which the logger is being requested.
1600          * @return an instance of {@link Logger Logger}  which will use the
1601          * provided resource bundle for message localization.
1602          *
1603          * @throws NullPointerException if {@code name} is {@code null} or
1604          *         {@code module} is {@code null}.
1605          * @throws SecurityException if a security manager is present and its
1606          *         {@code checkPermission} method doesn't allow the
1607          *         {@code RuntimePermission("loggerFinder")}.
1608          */
1609         public Logger getLocalizedLogger(String name, ResourceBundle bundle,
1610                                          Module module) {
1611             return new LocalizedLoggerWrapper<>(getLogger(name, module), bundle);
1612         }
1613 
1614         /**
1615          * Returns the {@code LoggerFinder} instance. There is one
1616          * single system-wide {@code LoggerFinder} instance in
1617          * the Java Runtime.  See the class specification of how the
1618          * {@link LoggerFinder LoggerFinder} implementation is located and
1619          * loaded.
1620 
1621          * @return the {@link LoggerFinder LoggerFinder} instance.
1622          * @throws SecurityException if a security manager is present and its
1623          *         {@code checkPermission} method doesn't allow the
1624          *         {@code RuntimePermission("loggerFinder")}.
1625          */
1626         public static LoggerFinder getLoggerFinder() {
1627             final SecurityManager sm = System.getSecurityManager();
1628             if (sm != null) {
1629                 sm.checkPermission(LOGGERFINDER_PERMISSION);
1630             }
1631             return accessProvider();
1632         }
1633 
1634 
1635         private static volatile LoggerFinder service;
1636         static LoggerFinder accessProvider() {
1637             // We do not need to synchronize: LoggerFinderLoader will
1638             // always return the same instance, so if we don't have it,
1639             // just fetch it again.
1640             if (service == null) {
1641                 PrivilegedAction<LoggerFinder> pa =
1642                         () -> LoggerFinderLoader.getLoggerFinder();
1643                 service = AccessController.doPrivileged(pa, null,
1644                         LOGGERFINDER_PERMISSION);
1645             }
1646             return service;
1647         }
1648 
1649     }
1650 
1651 
1652     /**
1653      * Returns an instance of {@link Logger Logger} for the caller's
1654      * use.
1655      *
1656      * @implSpec
1657      * Instances returned by this method route messages to loggers
1658      * obtained by calling {@link LoggerFinder#getLogger(java.lang.String,
1659      * java.lang.Module) LoggerFinder.getLogger(name, module)}, where
1660      * {@code module} is the caller's module.
1661      * In cases where {@code System.getLogger} is called from a context where
1662      * there is no caller frame on the stack (e.g when called directly
1663      * from a JNI attached thread), {@code IllegalCallerException} is thrown.
1664      * To obtain a logger in such a context, use an auxiliary class that will
1665      * implicitly be identified as the caller, or use the system {@link
1666      * LoggerFinder#getLoggerFinder() LoggerFinder} to obtain a logger instead.
1667      * Note that doing the latter may eagerly initialize the underlying
1668      * logging system.
1669      *
1670      * @apiNote
1671      * This method may defer calling the {@link
1672      * LoggerFinder#getLogger(java.lang.String, java.lang.Module)
1673      * LoggerFinder.getLogger} method to create an actual logger supplied by
1674      * the logging backend, for instance, to allow loggers to be obtained during
1675      * the system initialization time.
1676      *
1677      * @param name the name of the logger.
1678      * @return an instance of {@link Logger} that can be used by the calling
1679      *         class.
1680      * @throws NullPointerException if {@code name} is {@code null}.
1681      * @throws IllegalCallerException if there is no Java caller frame on the
1682      *         stack.
1683      *
1684      * @since 9
1685      */
1686     @CallerSensitive
1687     public static Logger getLogger(String name) {
1688         Objects.requireNonNull(name);
1689         final Class<?> caller = Reflection.getCallerClass();
1690         if (caller == null) {
1691             throw new IllegalCallerException("no caller frame");
1692         }
1693         return LazyLoggers.getLogger(name, caller.getModule());
1694     }
1695 
1696     /**
1697      * Returns a localizable instance of {@link Logger
1698      * Logger} for the caller's use.
1699      * The returned logger will use the provided resource bundle for message
1700      * localization.
1701      *
1702      * @implSpec
1703      * The returned logger will perform message localization as specified
1704      * by {@link LoggerFinder#getLocalizedLogger(java.lang.String,
1705      * java.util.ResourceBundle, java.lang.Module)
1706      * LoggerFinder.getLocalizedLogger(name, bundle, module)}, where
1707      * {@code module} is the caller's module.
1708      * In cases where {@code System.getLogger} is called from a context where
1709      * there is no caller frame on the stack (e.g when called directly
1710      * from a JNI attached thread), {@code IllegalCallerException} is thrown.
1711      * To obtain a logger in such a context, use an auxiliary class that
1712      * will implicitly be identified as the caller, or use the system {@link
1713      * LoggerFinder#getLoggerFinder() LoggerFinder} to obtain a logger instead.
1714      * Note that doing the latter may eagerly initialize the underlying
1715      * logging system.
1716      *
1717      * @apiNote
1718      * This method is intended to be used after the system is fully initialized.
1719      * This method may trigger the immediate loading and initialization
1720      * of the {@link LoggerFinder} service, which may cause issues if the
1721      * Java Runtime is not ready to initialize the concrete service
1722      * implementation yet.
1723      * System classes which may be loaded early in the boot sequence and
1724      * need to log localized messages should create a logger using
1725      * {@link #getLogger(java.lang.String)} and then use the log methods that
1726      * take a resource bundle as parameter.
1727      *
1728      * @param name    the name of the logger.
1729      * @param bundle  a resource bundle.
1730      * @return an instance of {@link Logger} which will use the provided
1731      * resource bundle for message localization.
1732      * @throws NullPointerException if {@code name} is {@code null} or
1733      *         {@code bundle} is {@code null}.
1734      * @throws IllegalCallerException if there is no Java caller frame on the
1735      *         stack.
1736      *
1737      * @since 9
1738      */
1739     @CallerSensitive
1740     public static Logger getLogger(String name, ResourceBundle bundle) {
1741         final ResourceBundle rb = Objects.requireNonNull(bundle);
1742         Objects.requireNonNull(name);
1743         final Class<?> caller = Reflection.getCallerClass();
1744         if (caller == null) {
1745             throw new IllegalCallerException("no caller frame");
1746         }
1747         final SecurityManager sm = System.getSecurityManager();
1748         // We don't use LazyLoggers if a resource bundle is specified.
1749         // Bootstrap sensitive classes in the JDK do not use resource bundles
1750         // when logging. This could be revisited later, if it needs to.
1751         if (sm != null) {
1752             final PrivilegedAction<Logger> pa =
1753                     () -> LoggerFinder.accessProvider()
1754                             .getLocalizedLogger(name, rb, caller.getModule());
1755             return AccessController.doPrivileged(pa, null,
1756                                          LoggerFinder.LOGGERFINDER_PERMISSION);
1757         }
1758         return LoggerFinder.accessProvider()
1759                 .getLocalizedLogger(name, rb, caller.getModule());
1760     }
1761 
1762     /**
1763      * Terminates the currently running Java Virtual Machine. The
1764      * argument serves as a status code; by convention, a nonzero status
1765      * code indicates abnormal termination.
1766      * <p>
1767      * This method calls the {@code exit} method in class
1768      * {@code Runtime}. This method never returns normally.
1769      * <p>
1770      * The call {@code System.exit(n)} is effectively equivalent to
1771      * the call:
1772      * <blockquote><pre>
1773      * Runtime.getRuntime().exit(n)
1774      * </pre></blockquote>
1775      *
1776      * @param      status   exit status.
1777      * @throws  SecurityException
1778      *        if a security manager exists and its {@code checkExit}
1779      *        method doesn't allow exit with the specified status.
1780      * @see        java.lang.Runtime#exit(int)
1781      */
1782     public static void exit(int status) {
1783         Runtime.getRuntime().exit(status);
1784     }
1785 
1786     /**
1787      * Runs the garbage collector in the Java Virtual Machine.
1788      * <p>
1789      * Calling the {@code gc} method suggests that the Java Virtual Machine
1790      * expend effort toward recycling unused objects in order to
1791      * make the memory they currently occupy available for reuse
1792      * by the Java Virtual Machine.
1793      * When control returns from the method call, the Java Virtual Machine
1794      * has made a best effort to reclaim space from all unused objects.
1795      * There is no guarantee that this effort will recycle any particular
1796      * number of unused objects, reclaim any particular amount of space, or
1797      * complete at any particular time, if at all, before the method returns or ever.
1798      * <p>
1799      * The call {@code System.gc()} is effectively equivalent to the
1800      * call:
1801      * <blockquote><pre>
1802      * Runtime.getRuntime().gc()
1803      * </pre></blockquote>
1804      *
1805      * @see     java.lang.Runtime#gc()
1806      */
1807     public static void gc() {
1808         Runtime.getRuntime().gc();
1809     }
1810 
1811     /**
1812      * Runs the finalization methods of any objects pending finalization.
1813      *
1814      * Calling this method suggests that the Java Virtual Machine expend
1815      * effort toward running the {@code finalize} methods of objects
1816      * that have been found to be discarded but whose {@code finalize}
1817      * methods have not yet been run. When control returns from the
1818      * method call, the Java Virtual Machine has made a best effort to
1819      * complete all outstanding finalizations.
1820      * <p>
1821      * The call {@code System.runFinalization()} is effectively
1822      * equivalent to the call:
1823      * <blockquote><pre>
1824      * Runtime.getRuntime().runFinalization()
1825      * </pre></blockquote>
1826      *
1827      * @see     java.lang.Runtime#runFinalization()
1828      */
1829     public static void runFinalization() {
1830         Runtime.getRuntime().runFinalization();
1831     }
1832 
1833     /**
1834      * Loads the native library specified by the filename argument.  The filename
1835      * argument must be an absolute path name.
1836      *
1837      * If the filename argument, when stripped of any platform-specific library
1838      * prefix, path, and file extension, indicates a library whose name is,
1839      * for example, L, and a native library called L is statically linked
1840      * with the VM, then the JNI_OnLoad_L function exported by the library
1841      * is invoked rather than attempting to load a dynamic library.
1842      * A filename matching the argument does not have to exist in the
1843      * file system.
1844      * See the <a href="{@docRoot}/../specs/jni/index.html"> JNI Specification</a>
1845      * for more details.
1846      *
1847      * Otherwise, the filename argument is mapped to a native library image in
1848      * an implementation-dependent manner.
1849      *
1850      * <p>
1851      * The call {@code System.load(name)} is effectively equivalent
1852      * to the call:
1853      * <blockquote><pre>
1854      * Runtime.getRuntime().load(name)
1855      * </pre></blockquote>
1856      *
1857      * @param      filename   the file to load.
1858      * @throws     SecurityException  if a security manager exists and its
1859      *             {@code checkLink} method doesn't allow
1860      *             loading of the specified dynamic library
1861      * @throws     UnsatisfiedLinkError  if either the filename is not an
1862      *             absolute path name, the native library is not statically
1863      *             linked with the VM, or the library cannot be mapped to
1864      *             a native library image by the host system.
1865      * @throws     NullPointerException if {@code filename} is {@code null}
1866      * @see        java.lang.Runtime#load(java.lang.String)
1867      * @see        java.lang.SecurityManager#checkLink(java.lang.String)
1868      */
1869     @CallerSensitive
1870     public static void load(String filename) {
1871         Runtime.getRuntime().load0(Reflection.getCallerClass(), filename);
1872     }
1873 
1874     /**
1875      * Loads the native library specified by the {@code libname}
1876      * argument.  The {@code libname} argument must not contain any platform
1877      * specific prefix, file extension or path. If a native library
1878      * called {@code libname} is statically linked with the VM, then the
1879      * JNI_OnLoad_{@code libname} function exported by the library is invoked.
1880      * See the <a href="{@docRoot}/../specs/jni/index.html"> JNI Specification</a>
1881      * for more details.
1882      *
1883      * Otherwise, the libname argument is loaded from a system library
1884      * location and mapped to a native library image in an implementation-
1885      * dependent manner.
1886      * <p>
1887      * The call {@code System.loadLibrary(name)} is effectively
1888      * equivalent to the call
1889      * <blockquote><pre>
1890      * Runtime.getRuntime().loadLibrary(name)
1891      * </pre></blockquote>
1892      *
1893      * @param      libname   the name of the library.
1894      * @throws     SecurityException  if a security manager exists and its
1895      *             {@code checkLink} method doesn't allow
1896      *             loading of the specified dynamic library
1897      * @throws     UnsatisfiedLinkError if either the libname argument
1898      *             contains a file path, the native library is not statically
1899      *             linked with the VM,  or the library cannot be mapped to a
1900      *             native library image by the host system.
1901      * @throws     NullPointerException if {@code libname} is {@code null}
1902      * @see        java.lang.Runtime#loadLibrary(java.lang.String)
1903      * @see        java.lang.SecurityManager#checkLink(java.lang.String)
1904      */
1905     @CallerSensitive
1906     public static void loadLibrary(String libname) {
1907         Runtime.getRuntime().loadLibrary0(Reflection.getCallerClass(), libname);
1908     }
1909 
1910     /**
1911      * Maps a library name into a platform-specific string representing
1912      * a native library.
1913      *
1914      * @param      libname the name of the library.
1915      * @return     a platform-dependent native library name.
1916      * @throws     NullPointerException if {@code libname} is {@code null}
1917      * @see        java.lang.System#loadLibrary(java.lang.String)
1918      * @see        java.lang.ClassLoader#findLibrary(java.lang.String)
1919      * @since      1.2
1920      */
1921     public static native String mapLibraryName(String libname);
1922 
1923     /**
1924      * Create PrintStream for stdout/err based on encoding.
1925      */
1926     private static PrintStream newPrintStream(FileOutputStream fos, String enc) {
1927        if (enc != null) {
1928             try {
1929                 return new PrintStream(new BufferedOutputStream(fos, 128), true, enc);
1930             } catch (UnsupportedEncodingException uee) {}
1931         }
1932         return new PrintStream(new BufferedOutputStream(fos, 128), true);
1933     }
1934 
1935     /**
1936      * Logs an exception/error at initialization time to stdout or stderr.
1937      *
1938      * @param printToStderr to print to stderr rather than stdout
1939      * @param printStackTrace to print the stack trace
1940      * @param msg the message to print before the exception, can be {@code null}
1941      * @param e the exception or error
1942      */
1943     private static void logInitException(boolean printToStderr,
1944                                          boolean printStackTrace,
1945                                          String msg,
1946                                          Throwable e) {
1947         if (VM.initLevel() < 1) {
1948             throw new InternalError("system classes not initialized");
1949         }
1950         PrintStream log = (printToStderr) ? err : out;
1951         if (msg != null) {
1952             log.println(msg);
1953         }
1954         if (printStackTrace) {
1955             e.printStackTrace(log);
1956         } else {
1957             log.println(e);
1958             for (Throwable suppressed : e.getSuppressed()) {
1959                 log.println("Suppressed: " + suppressed);
1960             }
1961             Throwable cause = e.getCause();
1962             if (cause != null) {
1963                 log.println("Caused by: " + cause);
1964             }
1965         }
1966     }
1967 
1968     /**
1969      * Create the Properties object from a map - masking out system properties
1970      * that are not intended for public access.
1971      */
1972     private static Properties createProperties(Map<String, String> initialProps) {
1973         Properties properties = new Properties(initialProps.size());
1974         for (var entry : initialProps.entrySet()) {
1975             String prop = entry.getKey();
1976             switch (prop) {
1977                 // Do not add private system properties to the Properties
1978                 case "sun.nio.MaxDirectMemorySize":
1979                 case "sun.nio.PageAlignDirectMemory":
1980                     // used by java.lang.Integer.IntegerCache
1981                 case "java.lang.Integer.IntegerCache.high":
1982                     // used by sun.launcher.LauncherHelper
1983                 case "sun.java.launcher.diag":
1984                     // used by jdk.internal.loader.ClassLoaders
1985                 case "jdk.boot.class.path.append":
1986                     break;
1987                 default:
1988                     properties.put(prop, entry.getValue());
1989             }
1990         }
1991         return properties;
1992     }
1993 
1994     /**
1995      * Initialize the system class.  Called after thread initialization.
1996      */
1997     private static void initPhase1() {
1998         // VM might invoke JNU_NewStringPlatform() to set those encoding
1999         // sensitive properties (user.home, user.name, boot.class.path, etc.)
2000         // during "props" initialization.
2001         // The charset is initialized in System.c and does not depend on the Properties.
2002         Map<String, String> tempProps = SystemProps.initProperties();
2003         VersionProps.init(tempProps);
2004 
2005         // There are certain system configurations that may be controlled by
2006         // VM options such as the maximum amount of direct memory and
2007         // Integer cache size used to support the object identity semantics
2008         // of autoboxing.  Typically, the library will obtain these values
2009         // from the properties set by the VM.  If the properties are for
2010         // internal implementation use only, these properties should be
2011         // masked from the system properties.
2012         //
2013         // Save a private copy of the system properties object that
2014         // can only be accessed by the internal implementation.
2015         VM.saveProperties(tempProps);
2016         props = createProperties(tempProps);
2017 
2018         StaticProperty.javaHome();          // Load StaticProperty to cache the property values
2019 
2020         lineSeparator = props.getProperty("line.separator");
2021 
2022         FileInputStream fdIn = new FileInputStream(FileDescriptor.in);
2023         FileOutputStream fdOut = new FileOutputStream(FileDescriptor.out);
2024         FileOutputStream fdErr = new FileOutputStream(FileDescriptor.err);
2025         setIn0(new BufferedInputStream(fdIn));
2026         setOut0(newPrintStream(fdOut, props.getProperty("sun.stdout.encoding")));
2027         setErr0(newPrintStream(fdErr, props.getProperty("sun.stderr.encoding")));
2028 
2029         // Setup Java signal handlers for HUP, TERM, and INT (where available).
2030         Terminator.setup();
2031 
2032         // Initialize any miscellaneous operating system settings that need to be
2033         // set for the class libraries. Currently this is no-op everywhere except
2034         // for Windows where the process-wide error mode is set before the java.io
2035         // classes are used.
2036         VM.initializeOSEnvironment();
2037 
2038         // The main thread is not added to its thread group in the same
2039         // way as other threads; we must do it ourselves here.
2040         Thread current = Thread.currentThread();
2041         current.getThreadGroup().add(current);
2042 
2043         // register shared secrets
2044         setJavaLangAccess();
2045 
2046         // Subsystems that are invoked during initialization can invoke
2047         // VM.isBooted() in order to avoid doing things that should
2048         // wait until the VM is fully initialized. The initialization level
2049         // is incremented from 0 to 1 here to indicate the first phase of
2050         // initialization has completed.
2051         // IMPORTANT: Ensure that this remains the last initialization action!
2052         VM.initLevel(1);
2053     }
2054 
2055     // @see #initPhase2()
2056     static ModuleLayer bootLayer;
2057 
2058     /*
2059      * Invoked by VM.  Phase 2 module system initialization.
2060      * Only classes in java.base can be loaded in this phase.
2061      *
2062      * @param printToStderr print exceptions to stderr rather than stdout
2063      * @param printStackTrace print stack trace when exception occurs
2064      *
2065      * @return JNI_OK for success, JNI_ERR for failure
2066      */
2067     private static int initPhase2(boolean printToStderr, boolean printStackTrace) {
2068         try {
2069             bootLayer = ModuleBootstrap.boot();
2070         } catch (Exception | Error e) {
2071             logInitException(printToStderr, printStackTrace,
2072                              "Error occurred during initialization of boot layer", e);
2073             return -1; // JNI_ERR
2074         }
2075 
2076         // module system initialized
2077         VM.initLevel(2);
2078 
2079         return 0; // JNI_OK
2080     }
2081 
2082     /*
2083      * Invoked by VM.  Phase 3 is the final system initialization:
2084      * 1. set security manager
2085      * 2. set system class loader
2086      * 3. set TCCL
2087      *
2088      * This method must be called after the module system initialization.
2089      * The security manager and system class loader may be a custom class from
2090      * the application classpath or modulepath.
2091      */
2092     private static void initPhase3() {
2093         String smProp = System.getProperty("java.security.manager");
2094         if (smProp != null) {
2095             switch (smProp) {
2096                 case "disallow":
2097                     allowSecurityManager = NEVER;
2098                     break;
2099                 case "allow":
2100                     allowSecurityManager = MAYBE;
2101                     break;
2102                 case "":
2103                 case "default":
2104                     setSecurityManager(new SecurityManager());
2105                     allowSecurityManager = MAYBE;
2106                     break;
2107                 default:
2108                     try {
2109                         ClassLoader cl = ClassLoader.getBuiltinAppClassLoader();
2110                         Class<?> c = Class.forName(smProp, false, cl);
2111                         Constructor<?> ctor = c.getConstructor();
2112                         // Must be a public subclass of SecurityManager with
2113                         // a public no-arg constructor
2114                         if (!SecurityManager.class.isAssignableFrom(c) ||
2115                             !Modifier.isPublic(c.getModifiers()) ||
2116                             !Modifier.isPublic(ctor.getModifiers())) {
2117                             throw new Error("Could not create SecurityManager: "
2118                                              + ctor.toString());
2119                         }
2120                         // custom security manager may be in non-exported package
2121                         ctor.setAccessible(true);
2122                         SecurityManager sm = (SecurityManager) ctor.newInstance();
2123                         setSecurityManager(sm);
2124                     } catch (Exception e) {
2125                         throw new InternalError("Could not create SecurityManager", e);
2126                     }
2127                     allowSecurityManager = MAYBE;
2128             }
2129         } else {
2130             allowSecurityManager = MAYBE;
2131         }
2132 
2133         // initializing the system class loader
2134         VM.initLevel(3);
2135 
2136         // system class loader initialized
2137         ClassLoader scl = ClassLoader.initSystemClassLoader();
2138 
2139         // set TCCL
2140         Thread.currentThread().setContextClassLoader(scl);
2141 
2142         // system is fully initialized
2143         VM.initLevel(4);
2144     }
2145 
2146     private static void setJavaLangAccess() {
2147         // Allow privileged classes outside of java.lang
2148         SharedSecrets.setJavaLangAccess(new JavaLangAccess() {
2149             public List<Method> getDeclaredPublicMethods(Class<?> klass, String name, Class<?>... parameterTypes) {
2150                 return klass.getDeclaredPublicMethods(name, parameterTypes);
2151             }
2152             public jdk.internal.reflect.ConstantPool getConstantPool(Class<?> klass) {
2153                 return klass.getConstantPool();
2154             }
2155             public boolean casAnnotationType(Class<?> klass, AnnotationType oldType, AnnotationType newType) {
2156                 return klass.casAnnotationType(oldType, newType);
2157             }
2158             public AnnotationType getAnnotationType(Class<?> klass) {
2159                 return klass.getAnnotationType();
2160             }
2161             public Map<Class<? extends Annotation>, Annotation> getDeclaredAnnotationMap(Class<?> klass) {
2162                 return klass.getDeclaredAnnotationMap();
2163             }
2164             public byte[] getRawClassAnnotations(Class<?> klass) {
2165                 return klass.getRawAnnotations();
2166             }
2167             public byte[] getRawClassTypeAnnotations(Class<?> klass) {
2168                 return klass.getRawTypeAnnotations();
2169             }
2170             public byte[] getRawExecutableTypeAnnotations(Executable executable) {
2171                 return Class.getExecutableTypeAnnotationBytes(executable);
2172             }
2173             public <E extends Enum<E>>
2174             E[] getEnumConstantsShared(Class<E> klass) {
2175                 return klass.getEnumConstantsShared();
2176             }
2177             public void blockedOn(Interruptible b) {
2178                 Thread.blockedOn(b);
2179             }
2180             public void registerShutdownHook(int slot, boolean registerShutdownInProgress, Runnable hook) {
2181                 Shutdown.add(slot, registerShutdownInProgress, hook);
2182             }
2183             public Thread newThreadWithAcc(Runnable target, AccessControlContext acc) {
2184                 return new Thread(target, acc);
2185             }
2186             @SuppressWarnings("deprecation")
2187             public void invokeFinalize(Object o) throws Throwable {
2188                 o.finalize();
2189             }
2190             public ConcurrentHashMap<?, ?> createOrGetClassLoaderValueMap(ClassLoader cl) {
2191                 return cl.createOrGetClassLoaderValueMap();
2192             }
2193             public Class<?> defineClass(ClassLoader loader, String name, byte[] b, ProtectionDomain pd, String source) {
2194                 return ClassLoader.defineClass1(loader, name, b, 0, b.length, pd, source);
2195             }
2196             public Class<?> findBootstrapClassOrNull(ClassLoader cl, String name) {
2197                 return cl.findBootstrapClassOrNull(name);
2198             }
2199             public Package definePackage(ClassLoader cl, String name, Module module) {
2200                 return cl.definePackage(name, module);
2201             }
2202             public String fastUUID(long lsb, long msb) {
2203                 return Long.fastUUID(lsb, msb);
2204             }
2205             public void addNonExportedPackages(ModuleLayer layer) {
2206                 SecurityManager.addNonExportedPackages(layer);
2207             }
2208             public void invalidatePackageAccessCache() {
2209                 SecurityManager.invalidatePackageAccessCache();
2210             }
2211             public Module defineModule(ClassLoader loader,
2212                                        ModuleDescriptor descriptor,
2213                                        URI uri) {
2214                 return new Module(null, loader, descriptor, uri);
2215             }
2216             public Module defineUnnamedModule(ClassLoader loader) {
2217                 return new Module(loader);
2218             }
2219             public void addReads(Module m1, Module m2) {
2220                 m1.implAddReads(m2);
2221             }
2222             public void addReadsAllUnnamed(Module m) {
2223                 m.implAddReadsAllUnnamed();
2224             }
2225             public void addExports(Module m, String pn, Module other) {
2226                 m.implAddExports(pn, other);
2227             }
2228             public void addExportsToAllUnnamed(Module m, String pn) {
2229                 m.implAddExportsToAllUnnamed(pn);
2230             }
2231             public void addOpens(Module m, String pn, Module other) {
2232                 m.implAddOpens(pn, other);
2233             }
2234             public void addOpensToAllUnnamed(Module m, String pn) {
2235                 m.implAddOpensToAllUnnamed(pn);
2236             }
2237             public void addOpensToAllUnnamed(Module m, Iterator<String> packages) {
2238                 m.implAddOpensToAllUnnamed(packages);
2239             }
2240             public void addUses(Module m, Class<?> service) {
2241                 m.implAddUses(service);
2242             }
2243             public boolean isReflectivelyExported(Module m, String pn, Module other) {
2244                 return m.isReflectivelyExported(pn, other);
2245             }
2246             public boolean isReflectivelyOpened(Module m, String pn, Module other) {
2247                 return m.isReflectivelyOpened(pn, other);
2248             }
2249             public ServicesCatalog getServicesCatalog(ModuleLayer layer) {
2250                 return layer.getServicesCatalog();
2251             }
2252             public Stream<ModuleLayer> layers(ModuleLayer layer) {
2253                 return layer.layers();
2254             }
2255             public Stream<ModuleLayer> layers(ClassLoader loader) {
2256                 return ModuleLayer.layers(loader);
2257             }
2258 
2259             public String newStringNoRepl(byte[] bytes, Charset cs) throws CharacterCodingException  {
2260                 return StringCoding.newStringNoRepl(bytes, cs);
2261             }
2262 
2263             public byte[] getBytesNoRepl(String s, Charset cs) throws CharacterCodingException {
2264                 return StringCoding.getBytesNoRepl(s, cs);
2265             }
2266 
2267             public String newStringUTF8NoRepl(byte[] bytes, int off, int len) {
2268                 return StringCoding.newStringUTF8NoRepl(bytes, off, len);
2269             }
2270 
2271             public byte[] getBytesUTF8NoRepl(String s) {
2272                 return StringCoding.getBytesUTF8NoRepl(s);
2273             }
2274 
2275             public void setCause(Throwable t, Throwable cause) {
2276                 t.setCause(cause);
2277             }
2278 
2279             public void loadLibrary(Class<?> caller, String library) {
2280                 assert library.indexOf(java.io.File.separatorChar) < 0;
2281                 ClassLoader.loadLibrary(caller, library, false);
2282             }
2283 
2284             public Thread currentCarrierThread() {
2285                 return Thread.currentCarrierThread();
2286             }
2287             public <R> R executeOnCarrierThread(Callable<R> task) throws Exception {
2288                 Thread t = Thread.currentCarrierThread();
2289                 Fiber<?> f = t.getFiber();
2290                 if (f != null) t.setFiber(null);
2291                 try {
2292                     return task.call();
2293                 } finally {
2294                     if (f != null) t.setFiber(f);
2295                 }
2296             }
2297             public <T> T getCarrierThreadLocal(ThreadLocal<T> local) {
2298                 return local.getCarrierThreadLocal();
2299             }
2300             public Fiber<?> getFiber(Thread t) {
2301                 if (t instanceof ShadowThread) {
2302                     return ((ShadowThread) t).fiber();
2303                 } else {
2304                     return null;
2305                 }
2306             }
2307             public Thread getShadowThread(Fiber<?> f) {
2308                 return f.shadowThreadOrNull();
2309             }
2310             public Object currentStrand() {
2311                 Thread thread = Thread.currentCarrierThread();
2312                 Fiber<?> fiber = thread.getFiber();
2313                 return (fiber != null) ? fiber : thread;
2314             }
2315             public void interrupt(Object strand) {
2316                 if (strand instanceof Fiber) {
2317                     ((Fiber) strand).interrupt();
2318                 } else {
2319                     ((Thread) strand).interrupt();
2320                 }
2321             }
2322             public boolean isInterrupted() {
2323                 Object strand = currentStrand();
2324                 if (strand instanceof Fiber) {
2325                     return ((Fiber) strand).isInterrupted();
2326                 } else {
2327                     return ((Thread) strand).isInterrupted();
2328                 }
2329             }
2330             public boolean clearInterrupt() {
2331                 if (currentStrand() instanceof Fiber) {
2332                     return Fiber.clearInterrupt();
2333                 } else {
2334                     return Thread.interrupted();
2335                 }
2336             }
2337             public void parkFiber() {
2338                 Fiber.park();
2339             }
2340             public void parkFiber(long nanos) {
2341                 Fiber.parkNanos(nanos);
2342             }
2343             public void unparkFiber(Fiber<?> fiber) {
2344                 fiber.unpark();
2345             }
2346         });
2347     }
2348 }