1 /*
2 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
3 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
4 *
5 *
6 *
7 *
8 *
9 *
10 *
11 *
12 *
13 *
14 *
15 *
16 *
17 *
18 *
19 *
20 *
21 *
22 *
23 *
24 */
25
26 package java.io;
27 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
28
29 /**
30 * A <code>BufferedInputStream</code> adds
31 * functionality to another input stream-namely,
32 * the ability to buffer the input and to
33 * support the <code>mark</code> and <code>reset</code>
34 * methods. When the <code>BufferedInputStream</code>
35 * is created, an internal buffer array is
36 * created. As bytes from the stream are read
37 * or skipped, the internal buffer is refilled
38 * as necessary from the contained input stream,
39 * many bytes at a time. The <code>mark</code>
40 * operation remembers a point in the input
41 * stream and the <code>reset</code> operation
42 * causes all the bytes read since the most
43 * recent <code>mark</code> operation to be
44 * reread before new bytes are taken from
45 * the contained input stream.
46 *
47 * @author Arthur van Hoff
48 * @since JDK1.0
49 */
50 public
51 class BufferedInputStream extends FilterInputStream {
52
53 private static int DEFAULT_BUFFER_SIZE = 8192;
54
55 /**
56 * The maximum size of array to allocate.
57 * Some VMs reserve some header words in an array.
58 * Attempts to allocate larger arrays may result in
59 * OutOfMemoryError: Requested array size exceeds VM limit
60 */
61 private static int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;
62
63 /**
64 * The internal buffer array where the data is stored. When necessary,
65 * it may be replaced by another array of
66 * a different size.
67 */
68 protected volatile byte buf[];
69
70 /**
71 * Atomic updater to provide compareAndSet for buf. This is
72 * necessary because closes can be asynchronous. We use nullness
73 * of buf[] as primary indicator that this stream is closed. (The
74 * "in" field is also nulled out on close.)
75 */
76 private static final
77 AtomicReferenceFieldUpdater<BufferedInputStream, byte[]> bufUpdater =
78 AtomicReferenceFieldUpdater.newUpdater
79 (BufferedInputStream.class, byte[].class, "buf");
80
81 /**
82 * The index one greater than the index of the last valid byte in
83 * the buffer.
84 * This value is always
85 * in the range <code>0</code> through <code>buf.length</code>;
86 * elements <code>buf[0]</code> through <code>buf[count-1]
87 * </code>contain buffered input data obtained
88 * from the underlying input stream.
89 */
90 protected int count;
91
92 /**
93 * The current position in the buffer. This is the index of the next
94 * character to be read from the <code>buf</code> array.
95 * <p>
96 * This value is always in the range <code>0</code>
97 * through <code>count</code>. If it is less
98 * than <code>count</code>, then <code>buf[pos]</code>
99 * is the next byte to be supplied as input;
100 * if it is equal to <code>count</code>, then
101 * the next <code>read</code> or <code>skip</code>
102 * operation will require more bytes to be
103 * read from the contained input stream.
104 *
105 * @see java.io.BufferedInputStream#buf
106 */
107 protected int pos;
108
109 /**
110 * The value of the <code>pos</code> field at the time the last
111 * <code>mark</code> method was called.
112 * <p>
113 * This value is always
114 * in the range <code>-1</code> through <code>pos</code>.
115 * If there is no marked position in the input
116 * stream, this field is <code>-1</code>. If
117 * there is a marked position in the input
118 * stream, then <code>buf[markpos]</code>
119 * is the first byte to be supplied as input
120 * after a <code>reset</code> operation. If
121 * <code>markpos</code> is not <code>-1</code>,
122 * then all bytes from positions <code>buf[markpos]</code>
123 * through <code>buf[pos-1]</code> must remain
124 * in the buffer array (though they may be
125 * moved to another place in the buffer array,
126 * with suitable adjustments to the values
127 * of <code>count</code>, <code>pos</code>,
128 * and <code>markpos</code>); they may not
129 * be discarded unless and until the difference
130 * between <code>pos</code> and <code>markpos</code>
131 * exceeds <code>marklimit</code>.
132 *
133 * @see java.io.BufferedInputStream#mark(int)
134 * @see java.io.BufferedInputStream#pos
135 */
136 protected int markpos = -1;
137
138 /**
139 * The maximum read ahead allowed after a call to the
140 * <code>mark</code> method before subsequent calls to the
141 * <code>reset</code> method fail.
142 * Whenever the difference between <code>pos</code>
143 * and <code>markpos</code> exceeds <code>marklimit</code>,
144 * then the mark may be dropped by setting
145 * <code>markpos</code> to <code>-1</code>.
146 *
147 * @see java.io.BufferedInputStream#mark(int)
148 * @see java.io.BufferedInputStream#reset()
149 */
150 protected int marklimit;
151
152 /**
153 * Check to make sure that underlying input stream has not been
154 * nulled out due to close; if not return it;
155 */
156 private InputStream getInIfOpen() throws IOException {
157 InputStream input = in;
158 if (input == null)
159 throw new IOException("Stream closed");
160 return input;
161 }
162
163 /**
164 * Check to make sure that buffer has not been nulled out due to
165 * close; if not return it;
166 */
167 private byte[] getBufIfOpen() throws IOException {
168 byte[] buffer = buf;
169 if (buffer == null)
170 throw new IOException("Stream closed");
171 return buffer;
172 }
173
174 /**
175 * Creates a <code>BufferedInputStream</code>
176 * and saves its argument, the input stream
177 * <code>in</code>, for later use. An internal
178 * buffer array is created and stored in <code>buf</code>.
179 *
180 * @param in the underlying input stream.
181 */
182 public BufferedInputStream(InputStream in) {
183 this(in, DEFAULT_BUFFER_SIZE);
184 }
185
186 /**
187 * Creates a <code>BufferedInputStream</code>
188 * with the specified buffer size,
189 * and saves its argument, the input stream
190 * <code>in</code>, for later use. An internal
191 * buffer array of length <code>size</code>
192 * is created and stored in <code>buf</code>.
193 *
194 * @param in the underlying input stream.
195 * @param size the buffer size.
196 * @exception IllegalArgumentException if {@code size <= 0}.
197 */
198 public BufferedInputStream(InputStream in, int size) {
199 super(in);
200 if (size <= 0) {
201 throw new IllegalArgumentException("Buffer size <= 0");
202 }
203 buf = new byte[size];
204 }
205
206 /**
207 * Fills the buffer with more data, taking into account
208 * shuffling and other tricks for dealing with marks.
209 * Assumes that it is being called by a synchronized method.
210 * This method also assumes that all data has already been read in,
211 * hence pos > count.
212 */
213 private void fill() throws IOException {
214 byte[] buffer = getBufIfOpen();
215 if (markpos < 0)
216 pos = 0; /* no mark: throw away the buffer */
217 else if (pos >= buffer.length) /* no room left in buffer */
218 if (markpos > 0) { /* can throw away early part of the buffer */
219 int sz = pos - markpos;
220 System.arraycopy(buffer, markpos, buffer, 0, sz);
221 pos = sz;
222 markpos = 0;
223 } else if (buffer.length >= marklimit) {
224 markpos = -1; /* buffer got too big, invalidate mark */
225 pos = 0; /* drop buffer contents */
226 } else if (buffer.length >= MAX_BUFFER_SIZE) {
227 throw new OutOfMemoryError("Required array size too large");
228 } else { /* grow buffer */
229 int nsz = (pos <= MAX_BUFFER_SIZE - pos) ?
230 pos * 2 : MAX_BUFFER_SIZE;
231 if (nsz > marklimit)
232 nsz = marklimit;
233 byte nbuf[] = new byte[nsz];
234 System.arraycopy(buffer, 0, nbuf, 0, pos);
235 if (!bufUpdater.compareAndSet(this, buffer, nbuf)) {
236 // Can't replace buf if there was an async close.
237 // Note: This would need to be changed if fill()
238 // is ever made accessible to multiple threads.
239 // But for now, the only way CAS can fail is via close.
240 // assert buf == null;
241 throw new IOException("Stream closed");
242 }
243 buffer = nbuf;
244 }
245 count = pos;
246 int n = getInIfOpen().read(buffer, pos, buffer.length - pos);
247 if (n > 0)
248 count = n + pos;
249 }
250
251 /**
252 * See
253 * the general contract of the <code>read</code>
254 * method of <code>InputStream</code>.
255 *
256 * @return the next byte of data, or <code>-1</code> if the end of the
257 * stream is reached.
258 * @exception IOException if this input stream has been closed by
259 * invoking its {@link #close()} method,
260 * or an I/O error occurs.
261 * @see java.io.FilterInputStream#in
262 */
263 public synchronized int read() throws IOException {
264 if (pos >= count) {
265 fill();
266 if (pos >= count)
267 return -1;
268 }
269 return getBufIfOpen()[pos++] & 0xff;
270 }
271
272 /**
273 * Read characters into a portion of an array, reading from the underlying
274 * stream at most once if necessary.
275 */
276 private int read1(byte[] b, int off, int len) throws IOException {
277 int avail = count - pos;
278 if (avail <= 0) {
279 /* If the requested length is at least as large as the buffer, and
280 if there is no mark/reset activity, do not bother to copy the
281 bytes into the local buffer. In this way buffered streams will
282 cascade harmlessly. */
283 if (len >= getBufIfOpen().length && markpos < 0) {
284 return getInIfOpen().read(b, off, len);
285 }
286 fill();
287 avail = count - pos;
288 if (avail <= 0) return -1;
289 }
290 int cnt = (avail < len) ? avail : len;
291 System.arraycopy(getBufIfOpen(), pos, b, off, cnt);
292 pos += cnt;
293 return cnt;
294 }
295
296 /**
297 * Reads bytes from this byte-input stream into the specified byte array,
298 * starting at the given offset.
299 *
300 * <p> This method implements the general contract of the corresponding
301 * <code>{@link InputStream#read(byte[], int, int) read}</code> method of
302 * the <code>{@link InputStream}</code> class. As an additional
303 * convenience, it attempts to read as many bytes as possible by repeatedly
304 * invoking the <code>read</code> method of the underlying stream. This
305 * iterated <code>read</code> continues until one of the following
306 * conditions becomes true: <ul>
307 *
308 * <li> The specified number of bytes have been read,
309 *
310 * <li> The <code>read</code> method of the underlying stream returns
311 * <code>-1</code>, indicating end-of-file, or
312 *
313 * <li> The <code>available</code> method of the underlying stream
314 * returns zero, indicating that further input requests would block.
315 *
316 * </ul> If the first <code>read</code> on the underlying stream returns
317 * <code>-1</code> to indicate end-of-file then this method returns
318 * <code>-1</code>. Otherwise this method returns the number of bytes
319 * actually read.
320 *
321 * <p> Subclasses of this class are encouraged, but not required, to
322 * attempt to read as many bytes as possible in the same fashion.
323 *
324 * @param b destination buffer.
325 * @param off offset at which to start storing bytes.
326 * @param len maximum number of bytes to read.
327 * @return the number of bytes read, or <code>-1</code> if the end of
328 * the stream has been reached.
329 * @exception IOException if this input stream has been closed by
330 * invoking its {@link #close()} method,
331 * or an I/O error occurs.
332 */
333 public synchronized int read(byte b[], int off, int len)
334 throws IOException
335 {
336 getBufIfOpen(); // Check for closed stream
337 if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
338 throw new IndexOutOfBoundsException();
339 } else if (len == 0) {
340 return 0;
341 }
342
343 int n = 0;
344 for (;;) {
345 int nread = read1(b, off + n, len - n);
346 if (nread <= 0)
347 return (n == 0) ? nread : n;
348 n += nread;
349 if (n >= len)
350 return n;
351 // if not closed but no bytes available, return
352 InputStream input = in;
353 if (input != null && input.available() <= 0)
354 return n;
355 }
356 }
357
358 /**
359 * See the general contract of the <code>skip</code>
360 * method of <code>InputStream</code>.
361 *
362 * @exception IOException if the stream does not support seek,
363 * or if this input stream has been closed by
364 * invoking its {@link #close()} method, or an
365 * I/O error occurs.
366 */
367 public synchronized long skip(long n) throws IOException {
368 getBufIfOpen(); // Check for closed stream
369 if (n <= 0) {
370 return 0;
371 }
372 long avail = count - pos;
373
374 if (avail <= 0) {
375 // If no mark position set then don't keep in buffer
376 if (markpos <0)
377 return getInIfOpen().skip(n);
378
379 // Fill in buffer to save bytes for reset
380 fill();
381 avail = count - pos;
382 if (avail <= 0)
383 return 0;
384 }
385
386 long skipped = (avail < n) ? avail : n;
387 pos += skipped;
388 return skipped;
389 }
390
391 /**
392 * Returns an estimate of the number of bytes that can be read (or
393 * skipped over) from this input stream without blocking by the next
394 * invocation of a method for this input stream. The next invocation might be
395 * the same thread or another thread. A single read or skip of this
396 * many bytes will not block, but may read or skip fewer bytes.
397 * <p>
398 * This method returns the sum of the number of bytes remaining to be read in
399 * the buffer (<code>count - pos</code>) and the result of calling the
400 * {@link java.io.FilterInputStream#in in}.available().
401 *
402 * @return an estimate of the number of bytes that can be read (or skipped
403 * over) from this input stream without blocking.
404 * @exception IOException if this input stream has been closed by
405 * invoking its {@link #close()} method,
406 * or an I/O error occurs.
407 */
408 public synchronized int available() throws IOException {
409 int n = count - pos;
410 int avail = getInIfOpen().available();
411 return n > (Integer.MAX_VALUE - avail)
412 ? Integer.MAX_VALUE
413 : n + avail;
414 }
415
416 /**
417 * See the general contract of the <code>mark</code>
418 * method of <code>InputStream</code>.
419 *
420 * @param readlimit the maximum limit of bytes that can be read before
421 * the mark position becomes invalid.
422 * @see java.io.BufferedInputStream#reset()
423 */
424 public synchronized void mark(int readlimit) {
425 marklimit = readlimit;
426 markpos = pos;
427 }
428
429 /**
430 * See the general contract of the <code>reset</code>
431 * method of <code>InputStream</code>.
432 * <p>
433 * If <code>markpos</code> is <code>-1</code>
434 * (no mark has been set or the mark has been
435 * invalidated), an <code>IOException</code>
436 * is thrown. Otherwise, <code>pos</code> is
437 * set equal to <code>markpos</code>.
438 *
439 * @exception IOException if this stream has not been marked or,
440 * if the mark has been invalidated, or the stream
441 * has been closed by invoking its {@link #close()}
442 * method, or an I/O error occurs.
443 * @see java.io.BufferedInputStream#mark(int)
444 */
445 public synchronized void reset() throws IOException {
446 getBufIfOpen(); // Cause exception if closed
447 if (markpos < 0)
448 throw new IOException("Resetting to invalid mark");
449 pos = markpos;
450 }
451
452 /**
453 * Tests if this input stream supports the <code>mark</code>
454 * and <code>reset</code> methods. The <code>markSupported</code>
455 * method of <code>BufferedInputStream</code> returns
456 * <code>true</code>.
457 *
458 * @return a <code>boolean</code> indicating if this stream type supports
459 * the <code>mark</code> and <code>reset</code> methods.
460 * @see java.io.InputStream#mark(int)
461 * @see java.io.InputStream#reset()
462 */
463 public boolean markSupported() {
464 return true;
465 }
466
467 /**
468 * Closes this input stream and releases any system resources
469 * associated with the stream.
470 * Once the stream has been closed, further read(), available(), reset(),
471 * or skip() invocations will throw an IOException.
472 * Closing a previously closed stream has no effect.
473 *
474 * @exception IOException if an I/O error occurs.
475 */
476 public void close() throws IOException {
477 byte[] buffer;
478 while ( (buffer = buf) != null) {
479 if (bufUpdater.compareAndSet(this, buffer, null)) {
480 InputStream input = in;
481 in = null;
482 if (input != null)
483 input.close();
484 return;
485 }
486 // Else retry in case a new buf was CASed in fill()
487 }
488 }
489 }
490