1 /*
  2  * Copyright (c) 1996, 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 
 26 package java.io;
 27 
 28 
 29 /**
 30  * Writes text to a character-output stream, buffering characters so as to
 31  * provide for the efficient writing of single characters, arrays, and strings.
 32  *
 33  * <p> The buffer size may be specified, or the default size may be accepted.
 34  * The default is large enough for most purposes.
 35  *
 36  * <p> A newLine() method is provided, which uses the platform's own notion of
 37  * line separator as defined by the system property {@code line.separator}.
 38  * Not all platforms use the newline character ('\n') to terminate lines.
 39  * Calling this method to terminate each output line is therefore preferred to
 40  * writing a newline character directly.
 41  *
 42  * <p> In general, a Writer sends its output immediately to the underlying
 43  * character or byte stream.  Unless prompt output is required, it is advisable
 44  * to wrap a BufferedWriter around any Writer whose write() operations may be
 45  * costly, such as FileWriters and OutputStreamWriters.  For example,
 46  *
 47  * <pre>
 48  * PrintWriter out
 49  *   = new PrintWriter(new BufferedWriter(new FileWriter("foo.out")));
 50  * </pre>
 51  *
 52  * will buffer the PrintWriter's output to the file.  Without buffering, each
 53  * invocation of a print() method would cause characters to be converted into
 54  * bytes that would then be written immediately to the file, which can be very
 55  * inefficient.
 56  *
 57  * @see PrintWriter
 58  * @see FileWriter
 59  * @see OutputStreamWriter
 60  * @see java.nio.file.Files#newBufferedWriter
 61  *
 62  * @author      Mark Reinhold
 63  * @since       1.1
 64  */
 65 
 66 public class BufferedWriter extends Writer {
 67 
 68     private Writer out;
 69 
 70     private char cb[];
 71     private int nChars, nextChar;
 72 
 73     private static int defaultCharBufferSize = 8192;
 74 
 75     /**
 76      * Creates a buffered character-output stream that uses a default-sized
 77      * output buffer.
 78      *
 79      * @param  out  A Writer
 80      */
 81     public BufferedWriter(Writer out) {
 82         this(out, defaultCharBufferSize);
 83     }
 84 
 85     /**
 86      * Creates a new buffered character-output stream that uses an output
 87      * buffer of the given size.
 88      *
 89      * @param  out  A Writer
 90      * @param  sz   Output-buffer size, a positive integer
 91      *
 92      * @throws     IllegalArgumentException  If {@code sz <= 0}
 93      */
 94     public BufferedWriter(Writer out, int sz) {
 95         super(out);
 96         if (sz <= 0)
 97             throw new IllegalArgumentException("Buffer size <= 0");
 98         this.out = out;
 99         cb = new char[sz];
100         nChars = sz;
101         nextChar = 0;
102     }
103 
104     /** Checks to make sure that the stream has not been closed */
105     private void ensureOpen() throws IOException {
106         if (out == null)
107             throw new IOException("Stream closed");
108     }
109 
110     /**
111      * Flushes the output buffer to the underlying character stream, without
112      * flushing the stream itself.  This method is non-private only so that it
113      * may be invoked by PrintStream.
114      */
115     void flushBuffer() throws IOException {
116         synchronized (lock) {
117             ensureOpen();
118             if (nextChar == 0)
119                 return;
120             out.write(cb, 0, nextChar);
121             nextChar = 0;
122         }
123     }
124 
125     /**
126      * Writes a single character.
127      *
128      * @throws     IOException  If an I/O error occurs
129      */
130     public void write(int c) throws IOException {
131         synchronized (lock) {
132             ensureOpen();
133             if (nextChar >= nChars)
134                 flushBuffer();
135             cb[nextChar++] = (char) c;
136         }
137     }
138 
139     /**
140      * Our own little min method, to avoid loading java.lang.Math if we've run
141      * out of file descriptors and we're trying to print a stack trace.
142      */
143     private int min(int a, int b) {
144         if (a < b) return a;
145         return b;
146     }
147 
148     /**
149      * Writes a portion of an array of characters.
150      *
151      * <p> Ordinarily this method stores characters from the given array into
152      * this stream's buffer, flushing the buffer to the underlying stream as
153      * needed.  If the requested length is at least as large as the buffer,
154      * however, then this method will flush the buffer and write the characters
155      * directly to the underlying stream.  Thus redundant
156      * {@code BufferedWriter}s will not copy data unnecessarily.
157      *
158      * @param  cbuf  A character array
159      * @param  off   Offset from which to start reading characters
160      * @param  len   Number of characters to write
161      *
162      * @throws  IndexOutOfBoundsException
163      *          If {@code off} is negative, or {@code len} is negative,
164      *          or {@code off + len} is negative or greater than the length
165      *          of the given array
166      *
167      * @throws  IOException  If an I/O error occurs
168      */
169     public void write(char[] cbuf, int off, int len) throws IOException {
170         synchronized (lock) {
171             ensureOpen();
172             if ((off < 0) || (off > cbuf.length) || (len < 0) ||
173                 ((off + len) > cbuf.length) || ((off + len) < 0)) {
174                 throw new IndexOutOfBoundsException();
175             } else if (len == 0) {
176                 return;
177             }
178 
179             if (len >= nChars) {
180                 /* If the request length exceeds the size of the output buffer,
181                    flush the buffer and then write the data directly.  In this
182                    way buffered streams will cascade harmlessly. */
183                 flushBuffer();
184                 out.write(cbuf, off, len);
185                 return;
186             }
187 
188             int b = off, t = off + len;
189             while (b < t) {
190                 int d = min(nChars - nextChar, t - b);
191                 System.arraycopy(cbuf, b, cb, nextChar, d);
192                 b += d;
193                 nextChar += d;
194                 if (nextChar >= nChars)
195                     flushBuffer();
196             }
197         }
198     }
199 
200     /**
201      * Writes a portion of a String.
202      *
203      * @implSpec
204      * While the specification of this method in the
205      * {@linkplain java.io.Writer#write(java.lang.String,int,int) superclass}
206      * recommends that an {@link IndexOutOfBoundsException} be thrown
207      * if {@code len} is negative or {@code off + len} is negative,
208      * the implementation in this class does not throw such an exception in
209      * these cases but instead simply writes no characters.
210      *
211      * @param  s     String to be written
212      * @param  off   Offset from which to start reading characters
213      * @param  len   Number of characters to be written
214      *
215      * @throws  IndexOutOfBoundsException
216      *          If {@code off} is negative,
217      *          or {@code off + len} is greater than the length
218      *          of the given string
219      *
220      * @throws  IOException  If an I/O error occurs
221      */
222     public void write(String s, int off, int len) throws IOException {
223         synchronized (lock) {
224             ensureOpen();
225 
226             int b = off, t = off + len;
227             while (b < t) {
228                 int d = min(nChars - nextChar, t - b);
229                 s.getChars(b, b + d, cb, nextChar);
230                 b += d;
231                 nextChar += d;
232                 if (nextChar >= nChars)
233                     flushBuffer();
234             }
235         }
236     }
237 
238     /**
239      * Writes a line separator.  The line separator string is defined by the
240      * system property {@code line.separator}, and is not necessarily a single
241      * newline ('\n') character.
242      *
243      * @throws     IOException  If an I/O error occurs
244      */
245     public void newLine() throws IOException {
246         write(System.lineSeparator());
247     }
248 
249     /**
250      * Flushes the stream.
251      *
252      * @throws     IOException  If an I/O error occurs
253      */
254     public void flush() throws IOException {
255         synchronized (lock) {
256             flushBuffer();
257             out.flush();
258         }
259     }
260 
261     @SuppressWarnings("try")
262     public void close() throws IOException {
263         synchronized (lock) {
264             if (out == null) {
265                 return;
266             }
267             try (Writer w = out) {
268                 flushBuffer();
269             } finally {
270                 out = null;
271                 cb = null;
272             }
273         }
274     }
275 }