1 /*
2 * Copyright (c) 2014, 2022, 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
26 package java.lang;
27
28 import java.lang.module.Configuration;
29 import java.lang.module.ModuleDescriptor;
30 import java.lang.module.ResolvedModule;
31 import java.util.ArrayDeque;
32 import java.util.ArrayList;
33 import java.util.Collections;
34 import java.util.Deque;
35 import java.util.HashMap;
36 import java.util.HashSet;
37 import java.util.List;
38 import java.util.Map;
39 import java.util.Objects;
40 import java.util.Optional;
41 import java.util.Set;
42 import java.util.concurrent.CopyOnWriteArrayList;
43 import java.util.function.Function;
44 import java.util.stream.Collectors;
45 import java.util.stream.Stream;
46
47 import jdk.internal.javac.PreviewFeature;
48 import jdk.internal.javac.Restricted;
49 import jdk.internal.loader.ClassLoaderValue;
50 import jdk.internal.loader.Loader;
51 import jdk.internal.loader.LoaderPool;
52 import jdk.internal.module.ServicesCatalog;
53 import jdk.internal.misc.CDS;
54 import jdk.internal.reflect.CallerSensitive;
55 import jdk.internal.reflect.Reflection;
56 import jdk.internal.vm.annotation.Stable;
57 import sun.security.util.SecurityConstants;
58
59 /**
60 * A layer of modules in the Java virtual machine.
61 *
62 * <p> A layer is created from a graph of modules in a {@link Configuration}
63 * and a function that maps each module to a {@link ClassLoader}.
64 * Creating a layer informs the Java virtual machine about the classes that
65 * may be loaded from the modules so that the Java virtual machine knows which
66 * module that each class is a member of. </p>
67 *
68 * <p> Creating a layer creates a {@link Module} object for each {@link
69 * ResolvedModule} in the configuration. For each resolved module that is
70 * {@link ResolvedModule#reads() read}, the {@code Module} {@link
71 * Module#canRead reads} the corresponding run-time {@code Module}, which may
72 * be in the same layer or a {@link #parents() parent} layer. </p>
73 *
74 * <p> The {@link #defineModulesWithOneLoader defineModulesWithOneLoader} and
75 * {@link #defineModulesWithManyLoaders defineModulesWithManyLoaders} methods
76 * provide convenient ways to create a module layer where all modules are
77 * mapped to a single class loader or where each module is mapped to its own
78 * class loader. The {@link #defineModules defineModules} method is for more
79 * advanced cases where modules are mapped to custom class loaders by means of
80 * a function specified to the method. Each of these methods has an instance
81 * and static variant. The instance methods create a layer with the receiver
82 * as the parent layer. The static methods are for more advanced cases where
83 * there can be more than one parent layer or where a {@link
84 * ModuleLayer.Controller Controller} is needed to control modules in the layer
85 * </p>
86 *
87 * <p> A Java virtual machine has at least one non-empty layer, the {@link
88 * #boot() boot} layer, that is created when the Java virtual machine is
89 * started. The boot layer contains module {@code java.base} and is the only
90 * layer in the Java virtual machine with a module named "{@code java.base}".
91 * The modules in the boot layer are mapped to the bootstrap class loader and
92 * other class loaders that are <a href="ClassLoader.html#builtinLoaders">
93 * built-in</a> into the Java virtual machine. The boot layer will often be
94 * the {@link #parents() parent} when creating additional layers. </p>
95 *
96 * <p> Each {@code Module} in a layer is created so that it {@link
97 * Module#isExported(String) exports} and {@link Module#isOpen(String) opens}
98 * the packages described by its {@link ModuleDescriptor}. Qualified exports
99 * (where a package is exported to a set of target modules rather than all
100 * modules) are reified when creating the layer as follows: </p>
101 * <ul>
102 * <li> If module {@code X} exports a package to {@code Y}, and if the
103 * runtime {@code Module} {@code X} reads {@code Module} {@code Y}, then
104 * the package is exported to {@code Module} {@code Y} (which may be in
105 * the same layer as {@code X} or a parent layer). </li>
106 *
107 * <li> If module {@code X} exports a package to {@code Y}, and if the
108 * runtime {@code Module} {@code X} does not read {@code Y} then target
109 * {@code Y} is located as if by invoking {@link #findModule(String)
110 * findModule} to find the module in the layer or its parent layers. If
111 * {@code Y} is found then the package is exported to the instance of
112 * {@code Y} that was found. If {@code Y} is not found then the qualified
113 * export is ignored. </li>
114 * </ul>
115 *
116 * <p> Qualified opens are handled in same way as qualified exports. </p>
117 *
118 * <p> As when creating a {@code Configuration},
119 * {@link ModuleDescriptor#isAutomatic() automatic} modules receive special
120 * treatment when creating a layer. An automatic module is created in the
121 * Java virtual machine as a {@code Module} that reads every unnamed {@code
122 * Module} in the Java virtual machine. </p>
123 *
124 * <p> Unless otherwise specified, passing a {@code null} argument to a method
125 * in this class causes a {@link NullPointerException NullPointerException} to
126 * be thrown. </p>
127 *
128 * <h2> Example </h2>
129 *
130 * <p> This example creates a configuration by resolving a module named
131 * "{@code myapp}" with the configuration for the boot layer as the parent. It
132 * then creates a new layer with the modules in this configuration. All modules
133 * are defined to the same class loader. </p>
134 *
135 * {@snippet :
136 * ModuleFinder finder = ModuleFinder.of(dir1, dir2, dir3);
137 * ModuleLayer parent = ModuleLayer.boot();
138 * Configuration cf = parent.configuration()
139 * .resolve(finder, ModuleFinder.of(), Set.of("myapp"));
140 * ClassLoader scl = ClassLoader.getSystemClassLoader();
141 * ModuleLayer layer = parent.defineModulesWithOneLoader(cf, scl);
142 * Class<?> c = layer.findLoader("myapp").loadClass("app.Main");
143 * }
144 *
145 * @since 9
146 * @see Module#getLayer()
147 */
148
149 public final class ModuleLayer {
150
151 // the empty layer (may be initialized from the CDS archive)
152 private static @Stable ModuleLayer EMPTY_LAYER;
153 static {
154 CDS.initializeFromArchive(ModuleLayer.class);
155 if (EMPTY_LAYER == null) {
156 // create a new empty layer if there is no archived version.
157 EMPTY_LAYER = new ModuleLayer(Configuration.empty(), List.of(), null);
158 }
159 }
160
161 // the configuration from which this layer was created
162 private final Configuration cf;
163
164 // parent layers, empty in the case of the empty layer
165 private final List<ModuleLayer> parents;
166
167 // maps module name to jlr.Module
168 private final Map<String, Module> nameToModule;
169
170 /**
171 * Creates a new module layer from the modules in the given configuration.
172 */
173 private ModuleLayer(Configuration cf,
174 List<ModuleLayer> parents,
175 Function<String, ClassLoader> clf)
176 {
177 this.cf = cf;
178 this.parents = parents; // no need to do defensive copy
179
180 Map<String, Module> map;
181 if (parents.isEmpty()) {
182 map = Map.of();
183 } else {
184 map = Module.defineModules(cf, clf, this);
185 }
186 this.nameToModule = map; // no need to do defensive copy
187 }
188
189 /**
190 * Controls a module layer. The static methods defined by {@link ModuleLayer}
191 * to create module layers return a {@code Controller} that can be used to
192 * control modules in the layer.
193 *
194 * <p> Unless otherwise specified, passing a {@code null} argument to a
195 * method in this class causes a {@link NullPointerException
196 * NullPointerException} to be thrown. </p>
197 *
198 * @apiNote Care should be taken with {@code Controller} objects, they
199 * should never be shared with untrusted code.
200 *
201 * @since 9
202 */
203 public static final class Controller {
204 private final ModuleLayer layer;
205
206 Controller(ModuleLayer layer) {
207 this.layer = layer;
208 }
209
210 /**
211 * Returns the layer that this object controls.
212 *
213 * @return the module layer
214 */
215 public ModuleLayer layer() {
216 return layer;
217 }
218
219 private void ensureInLayer(Module source) {
220 if (source.getLayer() != layer)
221 throw new IllegalArgumentException(source + " not in layer");
222 }
223
224
225 /**
226 * Updates module {@code source} in the layer to read module
227 * {@code target}. This method is a no-op if {@code source} already
228 * reads {@code target}.
229 *
230 * @implNote <em>Read edges</em> added by this method are <em>weak</em>
231 * and do not prevent {@code target} from being GC'ed when {@code source}
232 * is strongly reachable.
233 *
234 * @param source
235 * The source module
236 * @param target
237 * The target module to read
238 *
239 * @return This controller
240 *
241 * @throws IllegalArgumentException
242 * If {@code source} is not in the module layer
243 *
244 * @see Module#addReads
245 */
246 public Controller addReads(Module source, Module target) {
247 ensureInLayer(source);
248 source.implAddReads(target);
249 return this;
250 }
251
252 /**
253 * Updates module {@code source} in the layer to export a package to
254 * module {@code target}. This method is a no-op if {@code source}
255 * already exports the package to at least {@code target}.
256 *
257 * @param source
258 * The source module
259 * @param pn
260 * The package name
261 * @param target
262 * The target module
263 *
264 * @return This controller
265 *
266 * @throws IllegalArgumentException
267 * If {@code source} is not in the module layer or the package
268 * is not in the source module
269 *
270 * @see Module#addExports
271 */
272 public Controller addExports(Module source, String pn, Module target) {
273 ensureInLayer(source);
274 source.implAddExports(pn, target);
275 return this;
276 }
277
278 /**
279 * Updates module {@code source} in the layer to open a package to
280 * module {@code target}. This method is a no-op if {@code source}
281 * already opens the package to at least {@code target}.
282 *
283 * @param source
284 * The source module
285 * @param pn
286 * The package name
287 * @param target
288 * The target module
289 *
290 * @return This controller
291 *
292 * @throws IllegalArgumentException
293 * If {@code source} is not in the module layer or the package
294 * is not in the source module
295 *
296 * @see Module#addOpens
297 */
298 public Controller addOpens(Module source, String pn, Module target) {
299 ensureInLayer(source);
300 source.implAddOpens(pn, target);
301 return this;
302 }
303
304 /**
305 * Enables native access for a module in the layer if the caller's module
306 * has native access.
307 *
308 * <p> This method is <a href="foreign/package-summary.html#restricted"><em>restricted</em></a>.
309 * Restricted methods are unsafe, and, if used incorrectly, their use might crash
310 * the JVM or, worse, silently result in memory corruption.
311 *
312 * @param target
313 * The module to update
314 *
315 * @return This controller
316 *
317 * @throws IllegalArgumentException
318 * If {@code target} is not in the module layer
319 *
320 * @throws IllegalCallerException
321 * If the caller is in a module that does not have native access enabled
322 *
323 * @since 22
324 */
325 @CallerSensitive
326 @Restricted
327 public Controller enableNativeAccess(Module target) {
328 ensureInLayer(target);
329 Reflection.ensureNativeAccess(Reflection.getCallerClass(), Module.class,
330 "enableNativeAccess");
331 target.implAddEnableNativeAccess();
332 return this;
333 }
334 }
335
336
337 /**
338 * Creates a new module layer, with this layer as its parent, by defining the
339 * modules in the given {@code Configuration} to the Java virtual machine.
340 * This method creates one class loader and defines all modules to that
341 * class loader. The {@link ClassLoader#getParent() parent} of each class
342 * loader is the given parent class loader. This method works exactly as
343 * specified by the static {@link
344 * #defineModulesWithOneLoader(Configuration,List,ClassLoader)
345 * defineModulesWithOneLoader} method when invoked with this layer as the
346 * parent. In other words, if this layer is {@code thisLayer} then this
347 * method is equivalent to invoking:
348 * <pre> {@code
349 * ModuleLayer.defineModulesWithOneLoader(cf, List.of(thisLayer), parentLoader).layer();
350 * }</pre>
351 *
352 * @param cf
353 * The configuration for the layer
354 * @param parentLoader
355 * The parent class loader for the class loader created by this
356 * method; may be {@code null} for the bootstrap class loader
357 *
358 * @return The newly created layer
359 *
360 * @throws IllegalArgumentException
361 * If the given configuration has more than one parent or the parent
362 * of the configuration is not the configuration for this layer
363 * @throws LayerInstantiationException
364 * If the layer cannot be created for any of the reasons specified
365 * by the static {@code defineModulesWithOneLoader} method
366 * @throws SecurityException
367 * If {@code RuntimePermission("createClassLoader")} or
368 * {@code RuntimePermission("getClassLoader")} is denied by
369 * the security manager
370 *
371 * @see #findLoader
372 */
373 public ModuleLayer defineModulesWithOneLoader(Configuration cf,
374 ClassLoader parentLoader) {
375 return defineModulesWithOneLoader(cf, List.of(this), parentLoader).layer();
376 }
377
378
379 /**
380 * Creates a new module layer, with this layer as its parent, by defining the
381 * modules in the given {@code Configuration} to the Java virtual machine.
382 * Each module is defined to its own {@link ClassLoader} created by this
383 * method. The {@link ClassLoader#getParent() parent} of each class loader
384 * is the given parent class loader. This method works exactly as specified
385 * by the static {@link
386 * #defineModulesWithManyLoaders(Configuration,List,ClassLoader)
387 * defineModulesWithManyLoaders} method when invoked with this layer as the
388 * parent. In other words, if this layer is {@code thisLayer} then this
389 * method is equivalent to invoking:
390 * <pre> {@code
391 * ModuleLayer.defineModulesWithManyLoaders(cf, List.of(thisLayer), parentLoader).layer();
392 * }</pre>
393 *
394 * @param cf
395 * The configuration for the layer
396 * @param parentLoader
397 * The parent class loader for each of the class loaders created by
398 * this method; may be {@code null} for the bootstrap class loader
399 *
400 * @return The newly created layer
401 *
402 * @throws IllegalArgumentException
403 * If the given configuration has more than one parent or the parent
404 * of the configuration is not the configuration for this layer
405 * @throws LayerInstantiationException
406 * If the layer cannot be created for any of the reasons specified
407 * by the static {@code defineModulesWithManyLoaders} method
408 * @throws SecurityException
409 * If {@code RuntimePermission("createClassLoader")} or
410 * {@code RuntimePermission("getClassLoader")} is denied by
411 * the security manager
412 *
413 * @see #findLoader
414 */
415 public ModuleLayer defineModulesWithManyLoaders(Configuration cf,
416 ClassLoader parentLoader) {
417 return defineModulesWithManyLoaders(cf, List.of(this), parentLoader).layer();
418 }
419
420
421 /**
422 * Creates a new module layer, with this layer as its parent, by defining the
423 * modules in the given {@code Configuration} to the Java virtual machine.
424 * Each module is mapped, by name, to its class loader by means of the
425 * given function. This method works exactly as specified by the static
426 * {@link #defineModules(Configuration,List,Function) defineModules}
427 * method when invoked with this layer as the parent. In other words, if
428 * this layer is {@code thisLayer} then this method is equivalent to
429 * invoking:
430 * <pre> {@code
431 * ModuleLayer.defineModules(cf, List.of(thisLayer), clf).layer();
432 * }</pre>
433 *
434 * @param cf
435 * The configuration for the layer
436 * @param clf
437 * The function to map a module name to a class loader
438 *
439 * @return The newly created layer
440 *
441 * @throws IllegalArgumentException
442 * If the given configuration has more than one parent or the parent
443 * of the configuration is not the configuration for this layer
444 * @throws LayerInstantiationException
445 * If the layer cannot be created for any of the reasons specified
446 * by the static {@code defineModules} method
447 * @throws SecurityException
448 * If {@code RuntimePermission("getClassLoader")} is denied by
449 * the security manager
450 */
451 public ModuleLayer defineModules(Configuration cf,
452 Function<String, ClassLoader> clf) {
453 return defineModules(cf, List.of(this), clf).layer();
454 }
455
456 /**
457 * Creates a new module layer by defining the modules in the given {@code
458 * Configuration} to the Java virtual machine. This method creates one
459 * class loader and defines all modules to that class loader.
460 *
461 * <p> The class loader created by this method implements <em>direct
462 * delegation</em> when loading classes from modules. If the {@link
463 * ClassLoader#loadClass(String, boolean) loadClass} method is invoked to
464 * load a class then it uses the package name of the class to map it to a
465 * module. This may be a module in this layer and hence defined to the same
466 * class loader. It may be a package in a module in a parent layer that is
467 * exported to one or more of the modules in this layer. The class
468 * loader delegates to the class loader of the module, throwing {@code
469 * ClassNotFoundException} if not found by that class loader.
470 * When {@code loadClass} is invoked to load classes that do not map to a
471 * module then it delegates to the parent class loader. </p>
472 *
473 * <p> The class loader created by this method locates resources
474 * ({@link ClassLoader#getResource(String) getResource}, {@link
475 * ClassLoader#getResources(String) getResources}, and other resource
476 * methods) in all modules in the layer before searching the parent class
477 * loader. </p>
478 *
479 * <p> Attempting to create a layer with all modules defined to the same
480 * class loader can fail for the following reasons:
481 *
482 * <ul>
483 *
484 * <li><p> <em>Overlapping packages</em>: Two or more modules in the
485 * configuration have the same package. </p></li>
486 *
487 * <li><p> <em>Split delegation</em>: The resulting class loader would
488 * need to delegate to more than one class loader in order to load
489 * classes in a specific package. </p></li>
490 *
491 * </ul>
492 *
493 * <p> In addition, a layer cannot be created if the configuration contains
494 * a module named "{@code java.base}", or a module contains a package named
495 * "{@code java}" or a package with a name starting with "{@code java.}". </p>
496 *
497 * <p> If there is a security manager then the class loader created by
498 * this method will load classes and resources with privileges that are
499 * restricted by the calling context of this method. </p>
500 *
501 * @param cf
502 * The configuration for the layer
503 * @param parentLayers
504 * The list of parent layers in search order
505 * @param parentLoader
506 * The parent class loader for the class loader created by this
507 * method; may be {@code null} for the bootstrap class loader
508 *
509 * @return A controller that controls the newly created layer
510 *
511 * @throws IllegalArgumentException
512 * If the parent(s) of the given configuration do not match the
513 * configuration of the parent layers, including order
514 * @throws LayerInstantiationException
515 * If all modules cannot be defined to the same class loader for any
516 * of the reasons listed above
517 * @throws SecurityException
518 * If {@code RuntimePermission("createClassLoader")} or
519 * {@code RuntimePermission("getClassLoader")} is denied by
520 * the security manager
521 *
522 * @see #findLoader
523 */
524 public static Controller defineModulesWithOneLoader(Configuration cf,
525 List<ModuleLayer> parentLayers,
526 ClassLoader parentLoader)
527 {
528 List<ModuleLayer> parents = List.copyOf(parentLayers);
529 checkConfiguration(cf, parents);
530
531 checkCreateClassLoaderPermission();
532 checkGetClassLoaderPermission();
533
534 try {
535 Loader loader = new Loader(cf.modules(), parentLoader);
536 loader.initRemotePackageMap(cf, parents);
537 ModuleLayer layer = new ModuleLayer(cf, parents, mn -> loader);
538 return new Controller(layer);
539 } catch (IllegalArgumentException | IllegalStateException e) {
540 throw new LayerInstantiationException(e.getMessage());
541 }
542 }
543
544 /**
545 * Creates a new module layer by defining the modules in the given {@code
546 * Configuration} to the Java virtual machine. Each module is defined to
547 * its own {@link ClassLoader} created by this method. The {@link
548 * ClassLoader#getParent() parent} of each class loader is the given parent
549 * class loader.
550 *
551 * <p> The class loaders created by this method implement <em>direct
552 * delegation</em> when loading classes from modules. If the {@link
553 * ClassLoader#loadClass(String, boolean) loadClass} method is invoked to
554 * load a class then it uses the package name of the class to map it to a
555 * module. The package may be in the module defined to the class loader.
556 * The package may be exported by another module in this layer to the
557 * module defined to the class loader. It may be in a package exported by a
558 * module in a parent layer. The class loader delegates to the class loader
559 * of the module, throwing {@code ClassNotFoundException} if not found by
560 * that class loader. When {@code loadClass} is invoked to load a class
561 * that does not map to a module then it delegates to the parent class
562 * loader. </p>
563 *
564 * <p> The class loaders created by this method locate resources
565 * ({@link ClassLoader#getResource(String) getResource}, {@link
566 * ClassLoader#getResources(String) getResources}, and other resource
567 * methods) in the module defined to the class loader before searching
568 * the parent class loader. </p>
569 *
570 * <p> If there is a security manager then the class loaders created by
571 * this method will load classes and resources with privileges that are
572 * restricted by the calling context of this method. </p>
573 *
574 * @param cf
575 * The configuration for the layer
576 * @param parentLayers
577 * The list of parent layers in search order
578 * @param parentLoader
579 * The parent class loader for each of the class loaders created by
580 * this method; may be {@code null} for the bootstrap class loader
581 *
582 * @return A controller that controls the newly created layer
583 *
584 * @throws IllegalArgumentException
585 * If the parent(s) of the given configuration do not match the
586 * configuration of the parent layers, including order
587 * @throws LayerInstantiationException
588 * If the layer cannot be created because the configuration contains
589 * a module named "{@code java.base}" or a module contains a package
590 * named "{@code java}" or a package with a name starting with
591 * "{@code java.}"
592 *
593 * @throws SecurityException
594 * If {@code RuntimePermission("createClassLoader")} or
595 * {@code RuntimePermission("getClassLoader")} is denied by
596 * the security manager
597 *
598 * @see #findLoader
599 */
600 public static Controller defineModulesWithManyLoaders(Configuration cf,
601 List<ModuleLayer> parentLayers,
602 ClassLoader parentLoader)
603 {
604 List<ModuleLayer> parents = List.copyOf(parentLayers);
605 checkConfiguration(cf, parents);
606
607 checkCreateClassLoaderPermission();
608 checkGetClassLoaderPermission();
609
610 LoaderPool pool = new LoaderPool(cf, parents, parentLoader);
611 try {
612 ModuleLayer layer = new ModuleLayer(cf, parents, pool::loaderFor);
613 return new Controller(layer);
614 } catch (IllegalArgumentException | IllegalStateException e) {
615 throw new LayerInstantiationException(e.getMessage());
616 }
617 }
618
619 /**
620 * Creates a new module layer by defining the modules in the given {@code
621 * Configuration} to the Java virtual machine. The given function maps each
622 * module in the configuration, by name, to a class loader. Creating the
623 * layer informs the Java virtual machine about the classes that may be
624 * loaded so that the Java virtual machine knows which module that each
625 * class is a member of.
626 *
627 * <p> The class loader delegation implemented by the class loaders must
628 * respect module readability. The class loaders should be
629 * {@link ClassLoader#registerAsParallelCapable parallel-capable} so as to
630 * avoid deadlocks during class loading. In addition, the entity creating
631 * a new layer with this method should arrange that the class loaders be
632 * ready to load from these modules before there are any attempts to load
633 * classes or resources. </p>
634 *
635 * <p> Creating a layer can fail for the following reasons: </p>
636 *
637 * <ul>
638 *
639 * <li><p> Two or more modules with the same package are mapped to the
640 * same class loader. </p></li>
641 *
642 * <li><p> A module is mapped to a class loader that already has a
643 * module of the same name defined to it. </p></li>
644 *
645 * <li><p> A module is mapped to a class loader that has already
646 * defined types in any of the packages in the module. </p></li>
647 *
648 * </ul>
649 *
650 * <p> In addition, a layer cannot be created if the configuration contains
651 * a module named "{@code java.base}", a configuration contains a module
652 * with a package named "{@code java}" or a package name starting with
653 * "{@code java.}", or the function to map a module name to a class loader
654 * returns {@code null} or the {@linkplain ClassLoader#getPlatformClassLoader()
655 * platform class loader}. </p>
656 *
657 * <p> If the function to map a module name to class loader throws an error
658 * or runtime exception then it is propagated to the caller of this method.
659 * </p>
660 *
661 * @apiNote It is implementation specific as to whether creating a layer
662 * with this method is an atomic operation or not. Consequently it is
663 * possible for this method to fail with some modules, but not all, defined
664 * to the Java virtual machine.
665 *
666 * @param cf
667 * The configuration for the layer
668 * @param parentLayers
669 * The list of parent layers in search order
670 * @param clf
671 * The function to map a module name to a class loader
672 *
673 * @return A controller that controls the newly created layer
674 *
675 * @throws IllegalArgumentException
676 * If the parent(s) of the given configuration do not match the
677 * configuration of the parent layers, including order
678 * @throws LayerInstantiationException
679 * If creating the layer fails for any of the reasons listed above
680 * @throws SecurityException
681 * If {@code RuntimePermission("getClassLoader")} is denied by
682 * the security manager
683 */
684 public static Controller defineModules(Configuration cf,
685 List<ModuleLayer> parentLayers,
686 Function<String, ClassLoader> clf)
687 {
688 List<ModuleLayer> parents = List.copyOf(parentLayers);
689 checkConfiguration(cf, parents);
690 Objects.requireNonNull(clf);
691
692 checkGetClassLoaderPermission();
693
694 // The boot layer is checked during module system initialization
695 if (boot() != null) {
696 checkForDuplicatePkgs(cf, clf);
697 }
698
699 try {
700 ModuleLayer layer = new ModuleLayer(cf, parents, clf);
701 return new Controller(layer);
702 } catch (IllegalArgumentException | IllegalStateException e) {
703 throw new LayerInstantiationException(e.getMessage());
704 }
705 }
706
707
708 /**
709 * Checks that the parent configurations match the configuration of
710 * the parent layers.
711 */
712 private static void checkConfiguration(Configuration cf,
713 List<ModuleLayer> parentLayers)
714 {
715 Objects.requireNonNull(cf);
716
717 List<Configuration> parentConfigurations = cf.parents();
718 if (parentLayers.size() != parentConfigurations.size())
719 throw new IllegalArgumentException("wrong number of parents");
720
721 int index = 0;
722 for (ModuleLayer parent : parentLayers) {
723 if (parent.configuration() != parentConfigurations.get(index)) {
724 throw new IllegalArgumentException(
725 "Parent of configuration != configuration of this Layer");
726 }
727 index++;
728 }
729 }
730
731 private static void checkCreateClassLoaderPermission() {
732 @SuppressWarnings("removal")
733 SecurityManager sm = System.getSecurityManager();
734 if (sm != null)
735 sm.checkPermission(SecurityConstants.CREATE_CLASSLOADER_PERMISSION);
736 }
737
738 private static void checkGetClassLoaderPermission() {
739 @SuppressWarnings("removal")
740 SecurityManager sm = System.getSecurityManager();
741 if (sm != null)
742 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
743 }
744
745 /**
746 * Checks a configuration and the module-to-loader mapping to ensure that
747 * no two modules mapped to the same class loader have the same package.
748 * It also checks that no two automatic modules have the same package.
749 *
750 * @throws LayerInstantiationException
751 */
752 private static void checkForDuplicatePkgs(Configuration cf,
753 Function<String, ClassLoader> clf)
754 {
755 // HashMap allows null keys
756 Map<ClassLoader, Set<String>> loaderToPackages = new HashMap<>();
757 for (ResolvedModule resolvedModule : cf.modules()) {
758 ModuleDescriptor descriptor = resolvedModule.reference().descriptor();
759 ClassLoader loader = clf.apply(descriptor.name());
760
761 Set<String> loaderPackages
762 = loaderToPackages.computeIfAbsent(loader, k -> new HashSet<>());
763
764 for (String pkg : descriptor.packages()) {
765 boolean added = loaderPackages.add(pkg);
766 if (!added) {
767 throw fail("More than one module with package %s mapped" +
768 " to the same class loader", pkg);
769 }
770 }
771 }
772 }
773
774 /**
775 * Creates a LayerInstantiationException with the message formatted from
776 * the given format string and arguments.
777 */
778 private static LayerInstantiationException fail(String fmt, Object ... args) {
779 String msg = String.format(fmt, args);
780 return new LayerInstantiationException(msg);
781 }
782
783
784 /**
785 * Returns the configuration for this layer.
786 *
787 * @return The configuration for this layer
788 */
789 public Configuration configuration() {
790 return cf;
791 }
792
793 /**
794 * Returns an unmodifiable list of this layer's parents, in search
795 * order. If this is the {@linkplain #empty() empty layer} then an
796 * empty list is returned.
797 *
798 * @return A possibly-empty unmodifiable list of this layer's parents
799 */
800 public List<ModuleLayer> parents() {
801 return parents;
802 }
803
804
805 /**
806 * Returns an ordered stream of layers. The first element is this layer,
807 * the remaining elements are the parent layers in DFS order.
808 *
809 * @implNote For now, the assumption is that the number of elements will
810 * be very low and so this method does not use a specialized spliterator.
811 */
812 Stream<ModuleLayer> layers() {
813 List<ModuleLayer> allLayers = this.allLayers;
814 if (allLayers != null)
815 return allLayers.stream();
816
817 allLayers = new ArrayList<>();
818 Set<ModuleLayer> visited = new HashSet<>();
819 Deque<ModuleLayer> stack = new ArrayDeque<>();
820 visited.add(this);
821 stack.push(this);
822
823 while (!stack.isEmpty()) {
824 ModuleLayer layer = stack.pop();
825 allLayers.add(layer);
826
827 // push in reverse order
828 for (int i = layer.parents.size() - 1; i >= 0; i--) {
829 ModuleLayer parent = layer.parents.get(i);
830 if (visited.add(parent)) {
831 stack.push(parent);
832 }
833 }
834 }
835
836 this.allLayers = allLayers = Collections.unmodifiableList(allLayers);
837 return allLayers.stream();
838 }
839
840 private volatile List<ModuleLayer> allLayers;
841
842 /**
843 * Returns an unmodifiable set of the modules in this layer.
844 *
845 * @return A possibly-empty unmodifiable set of the modules in this layer
846 */
847 public Set<Module> modules() {
848 Set<Module> modules = this.modules;
849 if (modules == null) {
850 this.modules = modules = Set.copyOf(nameToModule.values());
851 }
852 return modules;
853 }
854
855 private volatile Set<Module> modules;
856
857
858 /**
859 * Returns the module with the given name in this layer, or if not in this
860 * layer, the {@linkplain #parents() parent} layers. Finding a module in
861 * parent layers is equivalent to invoking {@code findModule} on each
862 * parent, in search order, until the module is found or all parents have
863 * been searched. In a <em>tree of layers</em> then this is equivalent to
864 * a depth-first search.
865 *
866 * @param name
867 * The name of the module to find
868 *
869 * @return The module with the given name or an empty {@code Optional}
870 * if there isn't a module with this name in this layer or any
871 * parent layer
872 */
873 public Optional<Module> findModule(String name) {
874 Objects.requireNonNull(name);
875 if (this == EMPTY_LAYER)
876 return Optional.empty();
877 Module m = nameToModule.get(name);
878 if (m != null)
879 return Optional.of(m);
880
881 return layers()
882 .skip(1) // skip this layer
883 .map(l -> l.nameToModule.get(name))
884 .filter(Objects::nonNull)
885 .findAny();
886 }
887
888
889 /**
890 * Returns the {@code ClassLoader} for the module with the given name. If
891 * a module of the given name is not in this layer then the {@link #parents()
892 * parent} layers are searched in the manner specified by {@link
893 * #findModule(String) findModule}.
894 *
895 * <p> If there is a security manager then its {@code checkPermission}
896 * method is called with a {@code RuntimePermission("getClassLoader")}
897 * permission to check that the caller is allowed to get access to the
898 * class loader. </p>
899 *
900 * @apiNote This method does not return an {@code Optional<ClassLoader>}
901 * because `null` must be used to represent the bootstrap class loader.
902 *
903 * @param name
904 * The name of the module to find
905 *
906 * @return The ClassLoader that the module is defined to
907 *
908 * @throws IllegalArgumentException if a module of the given name is not
909 * defined in this layer or any parent of this layer
910 *
911 * @throws SecurityException if denied by the security manager
912 */
913 public ClassLoader findLoader(String name) {
914 Optional<Module> om = findModule(name);
915
916 // can't use map(Module::getClassLoader) as class loader can be null
917 if (om.isPresent()) {
918 return om.get().getClassLoader();
919 } else {
920 throw new IllegalArgumentException("Module " + name
921 + " not known to this layer");
922 }
923 }
924
925 /**
926 * Returns a string describing this module layer.
927 *
928 * @return A possibly empty string describing this module layer
929 */
930 @Override
931 public String toString() {
932 return modules().stream()
933 .map(Module::getName)
934 .collect(Collectors.joining(", "));
935 }
936
937 /**
938 * Returns the <em>empty</em> layer. There are no modules in the empty
939 * layer. It has no parents.
940 *
941 * @return The empty layer
942 */
943 public static ModuleLayer empty() {
944 return EMPTY_LAYER;
945 }
946
947
948 /**
949 * Returns the boot layer. The boot layer contains at least one module,
950 * {@code java.base}. Its parent is the {@link #empty() empty} layer.
951 *
952 * @apiNote This method returns {@code null} during startup and before
953 * the boot layer is fully initialized.
954 *
955 * @return The boot layer
956 */
957 public static ModuleLayer boot() {
958 return System.bootLayer;
959 }
960
961 /**
962 * Returns the ServicesCatalog for this Layer, creating it if not
963 * already created.
964 */
965 ServicesCatalog getServicesCatalog() {
966 ServicesCatalog servicesCatalog = this.servicesCatalog;
967 if (servicesCatalog != null)
968 return servicesCatalog;
969
970 synchronized (this) {
971 servicesCatalog = this.servicesCatalog;
972 if (servicesCatalog == null) {
973 servicesCatalog = ServicesCatalog.create();
974 for (Module m : nameToModule.values()) {
975 servicesCatalog.register(m);
976 }
977 this.servicesCatalog = servicesCatalog;
978 }
979 }
980
981 return servicesCatalog;
982 }
983
984 private volatile ServicesCatalog servicesCatalog;
985
986
987 /**
988 * Record that this layer has at least one module defined to the given
989 * class loader.
990 */
991 void bindToLoader(ClassLoader loader) {
992 // CLV.computeIfAbsent(loader, (cl, clv) -> new CopyOnWriteArrayList<>())
993 List<ModuleLayer> list = CLV.get(loader);
994 if (list == null) {
995 list = new CopyOnWriteArrayList<>();
996 List<ModuleLayer> previous = CLV.putIfAbsent(loader, list);
997 if (previous != null) list = previous;
998 }
999 list.add(this);
1000 }
1001
1002 /**
1003 * Returns a stream of the layers that have at least one module defined to
1004 * the given class loader.
1005 */
1006 static Stream<ModuleLayer> layers(ClassLoader loader) {
1007 List<ModuleLayer> list = CLV.get(loader);
1008 if (list != null) {
1009 return list.stream();
1010 } else {
1011 return Stream.empty();
1012 }
1013 }
1014
1015 // the list of layers with modules defined to a class loader
1016 private static final ClassLoaderValue<List<ModuleLayer>> CLV = new ClassLoaderValue<>();
1017 }