1/* 2 * Copyright (c) 1994, 2010, 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 26package java.io; 27import 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 */ 50public 51class BufferedInputStream extends FilterInputStream { 52 53 private static int defaultBufferSize = 8192; 54 55 /** 56 * The internal buffer array where the data is stored. When necessary, 57 * it may be replaced by another array of 58 * a different size. 59 */ 60 protected volatile byte buf[]; 61 62 /** 63 * Atomic updater to provide compareAndSet for buf. This is 64 * necessary because closes can be asynchronous. We use nullness 65 * of buf[] as primary indicator that this stream is closed. (The 66 * "in" field is also nulled out on close.) 67 */ 68 private static final 69 AtomicReferenceFieldUpdater<BufferedInputStream, byte[]> bufUpdater = 70 AtomicReferenceFieldUpdater.newUpdater 71 (BufferedInputStream.class, byte[].class, "buf"); 72 73 /** 74 * The index one greater than the index of the last valid byte in 75 * the buffer. 76 * This value is always 77 * in the range <code>0</code> through <code>buf.length</code>; 78 * elements <code>buf[0]</code> through <code>buf[count-1] 79 * </code>contain buffered input data obtained 80 * from the underlying input stream. 81 */ 82 protected int count; 83 84 /** 85 * The current position in the buffer. This is the index of the next 86 * character to be read from the <code>buf</code> array. 87 * <p> 88 * This value is always in the range <code>0</code> 89 * through <code>count</code>. If it is less 90 * than <code>count</code>, then <code>buf[pos]</code> 91 * is the next byte to be supplied as input; 92 * if it is equal to <code>count</code>, then 93 * the next <code>read</code> or <code>skip</code> 94 * operation will require more bytes to be 95 * read from the contained input stream. 96 * 97 * @see java.io.BufferedInputStream#buf 98 */ 99 protected int pos; 100 101 /** 102 * The value of the <code>pos</code> field at the time the last 103 * <code>mark</code> method was called. 104 * <p> 105 * This value is always 106 * in the range <code>-1</code> through <code>pos</code>. 107 * If there is no marked position in the input 108 * stream, this field is <code>-1</code>. If 109 * there is a marked position in the input 110 * stream, then <code>buf[markpos]</code> 111 * is the first byte to be supplied as input 112 * after a <code>reset</code> operation. If 113 * <code>markpos</code> is not <code>-1</code>, 114 * then all bytes from positions <code>buf[markpos]</code> 115 * through <code>buf[pos-1]</code> must remain 116 * in the buffer array (though they may be 117 * moved to another place in the buffer array, 118 * with suitable adjustments to the values 119 * of <code>count</code>, <code>pos</code>, 120 * and <code>markpos</code>); they may not 121 * be discarded unless and until the difference 122 * between <code>pos</code> and <code>markpos</code> 123 * exceeds <code>marklimit</code>. 124 * 125 * @see java.io.BufferedInputStream#mark(int) 126 * @see java.io.BufferedInputStream#pos 127 */ 128 protected int markpos = -1; 129 130 /** 131 * The maximum read ahead allowed after a call to the 132 * <code>mark</code> method before subsequent calls to the 133 * <code>reset</code> method fail. 134 * Whenever the difference between <code>pos</code> 135 * and <code>markpos</code> exceeds <code>marklimit</code>, 136 * then the mark may be dropped by setting 137 * <code>markpos</code> to <code>-1</code>. 138 * 139 * @see java.io.BufferedInputStream#mark(int) 140 * @see java.io.BufferedInputStream#reset() 141 */ 142 protected int marklimit; 143 144 /** 145 * Check to make sure that underlying input stream has not been 146 * nulled out due to close; if not return it; 147 */ 148 private InputStream getInIfOpen() throws IOException { 149 InputStream input = in; 150 if (input == null) 151 throw new IOException("Stream closed"); 152 return input; 153 } 154 155 /** 156 * Check to make sure that buffer has not been nulled out due to 157 * close; if not return it; 158 */ 159 private byte[] getBufIfOpen() throws IOException { 160 byte[] buffer = buf; 161 if (buffer == null) 162 throw new IOException("Stream closed"); 163 return buffer; 164 } 165 166 /** 167 * Creates a <code>BufferedInputStream</code> 168 * and saves its argument, the input stream 169 * <code>in</code>, for later use. An internal 170 * buffer array is created and stored in <code>buf</code>. 171 * 172 * @param in the underlying input stream. 173 */ 174 public BufferedInputStream(InputStream in) { 175 this(in, defaultBufferSize); 176 } 177 178 /** 179 * Creates a <code>BufferedInputStream</code> 180 * with the specified buffer size, 181 * and saves its argument, the input stream 182 * <code>in</code>, for later use. An internal 183 * buffer array of length <code>size</code> 184 * is created and stored in <code>buf</code>. 185 * 186 * @param in the underlying input stream. 187 * @param size the buffer size. 188 * @exception IllegalArgumentException if size <= 0. 189 */ 190 public BufferedInputStream(InputStream in, int size) { 191 super(in); 192 if (size <= 0) { 193 throw new IllegalArgumentException("Buffer size <= 0"); 194 } 195 buf = new byte[size]; 196 } 197 198 /** 199 * Fills the buffer with more data, taking into account 200 * shuffling and other tricks for dealing with marks. 201 * Assumes that it is being called by a synchronized method. 202 * This method also assumes that all data has already been read in, 203 * hence pos > count. 204 */ 205 private void fill() throws IOException { 206 byte[] buffer = getBufIfOpen(); 207 if (markpos < 0) 208 pos = 0; /* no mark: throw away the buffer */ 209 else if (pos >= buffer.length) /* no room left in buffer */ 210 if (markpos > 0) { /* can throw away early part of the buffer */ 211 int sz = pos - markpos; 212 System.arraycopy(buffer, markpos, buffer, 0, sz); 213 pos = sz; 214 markpos = 0; 215 } else if (buffer.length >= marklimit) { 216 markpos = -1; /* buffer got too big, invalidate mark */ 217 pos = 0; /* drop buffer contents */ 218 } else { /* grow buffer */ 219 int nsz = pos * 2; 220 if (nsz > marklimit) 221 nsz = marklimit; 222 byte nbuf[] = new byte[nsz]; 223 System.arraycopy(buffer, 0, nbuf, 0, pos); 224 if (!bufUpdater.compareAndSet(this, buffer, nbuf)) { 225 // Can't replace buf if there was an async close. 226 // Note: This would need to be changed if fill() 227 // is ever made accessible to multiple threads. 228 // But for now, the only way CAS can fail is via close. 229 // assert buf == null; 230 throw new IOException("Stream closed"); 231 } 232 buffer = nbuf; 233 } 234 count = pos; 235 int n = getInIfOpen().read(buffer, pos, buffer.length - pos); 236 if (n > 0) 237 count = n + pos; 238 } 239 240 /** 241 * See 242 * the general contract of the <code>read</code> 243 * method of <code>InputStream</code>. 244 * 245 * @return the next byte of data, or <code>-1</code> if the end of the 246 * stream is reached. 247 * @exception IOException if this input stream has been closed by 248 * invoking its {@link #close()} method, 249 * or an I/O error occurs. 250 * @see java.io.FilterInputStream#in 251 */ 252 public synchronized int read() throws IOException { 253 if (pos >= count) { 254 fill(); 255 if (pos >= count) 256 return -1; 257 } 258 return getBufIfOpen()[pos++] & 0xff; 259 } 260 261 /** 262 * Read characters into a portion of an array, reading from the underlying 263 * stream at most once if necessary. 264 */ 265 private int read1(byte[] b, int off, int len) throws IOException { 266 int avail = count - pos; 267 if (avail <= 0) { 268 /* If the requested length is at least as large as the buffer, and 269 if there is no mark/reset activity, do not bother to copy the 270 bytes into the local buffer. In this way buffered streams will 271 cascade harmlessly. */ 272 if (len >= getBufIfOpen().length && markpos < 0) { 273 return getInIfOpen().read(b, off, len); 274 } 275 fill(); 276 avail = count - pos; 277 if (avail <= 0) return -1; 278 } 279 int cnt = (avail < len) ? avail : len; 280 System.arraycopy(getBufIfOpen(), pos, b, off, cnt); 281 pos += cnt; 282 return cnt; 283 } 284 285 /** 286 * Reads bytes from this byte-input stream into the specified byte array, 287 * starting at the given offset. 288 * 289 * <p> This method implements the general contract of the corresponding 290 * <code>{@link InputStream#read(byte[], int, int) read}</code> method of 291 * the <code>{@link InputStream}</code> class. As an additional 292 * convenience, it attempts to read as many bytes as possible by repeatedly 293 * invoking the <code>read</code> method of the underlying stream. This 294 * iterated <code>read</code> continues until one of the following 295 * conditions becomes true: <ul> 296 * 297 * <li> The specified number of bytes have been read, 298 * 299 * <li> The <code>read</code> method of the underlying stream returns 300 * <code>-1</code>, indicating end-of-file, or 301 * 302 * <li> The <code>available</code> method of the underlying stream 303 * returns zero, indicating that further input requests would block. 304 * 305 * </ul> If the first <code>read</code> on the underlying stream returns 306 * <code>-1</code> to indicate end-of-file then this method returns 307 * <code>-1</code>. Otherwise this method returns the number of bytes 308 * actually read. 309 * 310 * <p> Subclasses of this class are encouraged, but not required, to 311 * attempt to read as many bytes as possible in the same fashion. 312 * 313 * @param b destination buffer. 314 * @param off offset at which to start storing bytes. 315 * @param len maximum number of bytes to read. 316 * @return the number of bytes read, or <code>-1</code> if the end of 317 * the stream has been reached. 318 * @exception IOException if this input stream has been closed by 319 * invoking its {@link #close()} method, 320 * or an I/O error occurs. 321 */ 322 public synchronized int read(byte b[], int off, int len) 323 throws IOException 324 { 325 getBufIfOpen(); // Check for closed stream 326 if ((off | len | (off + len) | (b.length - (off + len))) < 0) { 327 throw new IndexOutOfBoundsException(); 328 } else if (len == 0) { 329 return 0; 330 } 331 332 int n = 0; 333 for (;;) { 334 int nread = read1(b, off + n, len - n); 335 if (nread <= 0) 336 return (n == 0) ? nread : n; 337 n += nread; 338 if (n >= len) 339 return n; 340 // if not closed but no bytes available, return 341 InputStream input = in; 342 if (input != null && input.available() <= 0) 343 return n; 344 } 345 } 346 347 /** 348 * See the general contract of the <code>skip</code> 349 * method of <code>InputStream</code>. 350 * 351 * @exception IOException if the stream does not support seek, 352 * or if this input stream has been closed by 353 * invoking its {@link #close()} method, or an 354 * I/O error occurs. 355 */ 356 public synchronized long skip(long n) throws IOException { 357 getBufIfOpen(); // Check for closed stream 358 if (n <= 0) { 359 return 0; 360 } 361 long avail = count - pos; 362 363 if (avail <= 0) { 364 // If no mark position set then don't keep in buffer 365 if (markpos <0) 366 return getInIfOpen().skip(n); 367 368 // Fill in buffer to save bytes for reset 369 fill(); 370 avail = count - pos; 371 if (avail <= 0) 372 return 0; 373 } 374 375 long skipped = (avail < n) ? avail : n; 376 pos += skipped; 377 return skipped; 378 } 379 380 /** 381 * Returns an estimate of the number of bytes that can be read (or 382 * skipped over) from this input stream without blocking by the next 383 * invocation of a method for this input stream. The next invocation might be 384 * the same thread or another thread. A single read or skip of this 385 * many bytes will not block, but may read or skip fewer bytes. 386 * <p> 387 * This method returns the sum of the number of bytes remaining to be read in 388 * the buffer (<code>count - pos</code>) and the result of calling the 389 * {@link java.io.FilterInputStream#in in}.available(). 390 * 391 * @return an estimate of the number of bytes that can be read (or skipped 392 * over) from this input stream without blocking. 393 * @exception IOException if this input stream has been closed by 394 * invoking its {@link #close()} method, 395 * or an I/O error occurs. 396 */ 397 public synchronized int available() throws IOException { 398 int n = count - pos; 399 int avail = getInIfOpen().available(); 400 return n > (Integer.MAX_VALUE - avail) 401 ? Integer.MAX_VALUE 402 : n + avail; 403 } 404 405 /** 406 * See the general contract of the <code>mark</code> 407 * method of <code>InputStream</code>. 408 * 409 * @param readlimit the maximum limit of bytes that can be read before 410 * the mark position becomes invalid. 411 * @see java.io.BufferedInputStream#reset() 412 */ 413 public synchronized void mark(int readlimit) { 414 marklimit = readlimit; 415 markpos = pos; 416 } 417 418 /** 419 * See the general contract of the <code>reset</code> 420 * method of <code>InputStream</code>. 421 * <p> 422 * If <code>markpos</code> is <code>-1</code> 423 * (no mark has been set or the mark has been 424 * invalidated), an <code>IOException</code> 425 * is thrown. Otherwise, <code>pos</code> is 426 * set equal to <code>markpos</code>. 427 * 428 * @exception IOException if this stream has not been marked or, 429 * if the mark has been invalidated, or the stream 430 * has been closed by invoking its {@link #close()} 431 * method, or an I/O error occurs. 432 * @see java.io.BufferedInputStream#mark(int) 433 */ 434 public synchronized void reset() throws IOException { 435 getBufIfOpen(); // Cause exception if closed 436 if (markpos < 0) 437 throw new IOException("Resetting to invalid mark"); 438 pos = markpos; 439 } 440 441 /** 442 * Tests if this input stream supports the <code>mark</code> 443 * and <code>reset</code> methods. The <code>markSupported</code> 444 * method of <code>BufferedInputStream</code> returns 445 * <code>true</code>. 446 * 447 * @return a <code>boolean</code> indicating if this stream type supports 448 * the <code>mark</code> and <code>reset</code> methods. 449 * @see java.io.InputStream#mark(int) 450 * @see java.io.InputStream#reset() 451 */ 452 public boolean markSupported() { 453 return true; 454 } 455 456 /** 457 * Closes this input stream and releases any system resources 458 * associated with the stream. 459 * Once the stream has been closed, further read(), available(), reset(), 460 * or skip() invocations will throw an IOException. 461 * Closing a previously closed stream has no effect. 462 * 463 * @exception IOException if an I/O error occurs. 464 */ 465 public void close() throws IOException { 466 byte[] buffer; 467 while ( (buffer = buf) != null) { 468 if (bufUpdater.compareAndSet(this, buffer, null)) { 469 InputStream input = in; 470 in = null; 471 if (input != null) 472 input.close(); 473 return; 474 } 475 // Else retry in case a new buf was CASed in fill() 476 } 477 } 478} 479