J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 1994-2006 Sun Microsystems, Inc. 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. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | |
| 26 | package java.io; |
| 27 | |
| 28 | /** |
| 29 | * A <code>PushbackInputStream</code> adds |
| 30 | * functionality to another input stream, namely |
| 31 | * the ability to "push back" or "unread" |
| 32 | * one byte. This is useful in situations where |
| 33 | * it is convenient for a fragment of code |
| 34 | * to read an indefinite number of data bytes |
| 35 | * that are delimited by a particular byte |
| 36 | * value; after reading the terminating byte, |
| 37 | * the code fragment can "unread" it, so that |
| 38 | * the next read operation on the input stream |
| 39 | * will reread the byte that was pushed back. |
| 40 | * For example, bytes representing the characters |
| 41 | * constituting an identifier might be terminated |
| 42 | * by a byte representing an operator character; |
| 43 | * a method whose job is to read just an identifier |
| 44 | * can read until it sees the operator and |
| 45 | * then push the operator back to be re-read. |
| 46 | * |
| 47 | * @author David Connelly |
| 48 | * @author Jonathan Payne |
| 49 | * @since JDK1.0 |
| 50 | */ |
| 51 | public |
| 52 | class PushbackInputStream extends FilterInputStream { |
| 53 | /** |
| 54 | * The pushback buffer. |
| 55 | * @since JDK1.1 |
| 56 | */ |
| 57 | protected byte[] buf; |
| 58 | |
| 59 | /** |
| 60 | * The position within the pushback buffer from which the next byte will |
| 61 | * be read. When the buffer is empty, <code>pos</code> is equal to |
| 62 | * <code>buf.length</code>; when the buffer is full, <code>pos</code> is |
| 63 | * equal to zero. |
| 64 | * |
| 65 | * @since JDK1.1 |
| 66 | */ |
| 67 | protected int pos; |
| 68 | |
| 69 | /** |
| 70 | * Check to make sure that this stream has not been closed |
| 71 | */ |
| 72 | private void ensureOpen() throws IOException { |
| 73 | if (in == null) |
| 74 | throw new IOException("Stream closed"); |
| 75 | } |
| 76 | |
| 77 | /** |
| 78 | * Creates a <code>PushbackInputStream</code> |
| 79 | * with a pushback buffer of the specified <code>size</code>, |
| 80 | * and saves its argument, the input stream |
| 81 | * <code>in</code>, for later use. Initially, |
| 82 | * there is no pushed-back byte (the field |
| 83 | * <code>pushBack</code> is initialized to |
| 84 | * <code>-1</code>). |
| 85 | * |
| 86 | * @param in the input stream from which bytes will be read. |
| 87 | * @param size the size of the pushback buffer. |
| 88 | * @exception IllegalArgumentException if size is <= 0 |
| 89 | * @since JDK1.1 |
| 90 | */ |
| 91 | public PushbackInputStream(InputStream in, int size) { |
| 92 | super(in); |
| 93 | if (size <= 0) { |
| 94 | throw new IllegalArgumentException("size <= 0"); |
| 95 | } |
| 96 | this.buf = new byte[size]; |
| 97 | this.pos = size; |
| 98 | } |
| 99 | |
| 100 | /** |
| 101 | * Creates a <code>PushbackInputStream</code> |
| 102 | * and saves its argument, the input stream |
| 103 | * <code>in</code>, for later use. Initially, |
| 104 | * there is no pushed-back byte (the field |
| 105 | * <code>pushBack</code> is initialized to |
| 106 | * <code>-1</code>). |
| 107 | * |
| 108 | * @param in the input stream from which bytes will be read. |
| 109 | */ |
| 110 | public PushbackInputStream(InputStream in) { |
| 111 | this(in, 1); |
| 112 | } |
| 113 | |
| 114 | /** |
| 115 | * Reads the next byte of data from this input stream. The value |
| 116 | * byte is returned as an <code>int</code> in the range |
| 117 | * <code>0</code> to <code>255</code>. If no byte is available |
| 118 | * because the end of the stream has been reached, the value |
| 119 | * <code>-1</code> is returned. This method blocks until input data |
| 120 | * is available, the end of the stream is detected, or an exception |
| 121 | * is thrown. |
| 122 | * |
| 123 | * <p> This method returns the most recently pushed-back byte, if there is |
| 124 | * one, and otherwise calls the <code>read</code> method of its underlying |
| 125 | * input stream and returns whatever value that method returns. |
| 126 | * |
| 127 | * @return the next byte of data, or <code>-1</code> if the end of the |
| 128 | * stream has been reached. |
| 129 | * @exception IOException if this input stream has been closed by |
| 130 | * invoking its {@link #close()} method, |
| 131 | * or an I/O error occurs. |
| 132 | * @see java.io.InputStream#read() |
| 133 | */ |
| 134 | public int read() throws IOException { |
| 135 | ensureOpen(); |
| 136 | if (pos < buf.length) { |
| 137 | return buf[pos++] & 0xff; |
| 138 | } |
| 139 | return super.read(); |
| 140 | } |
| 141 | |
| 142 | /** |
| 143 | * Reads up to <code>len</code> bytes of data from this input stream into |
| 144 | * an array of bytes. This method first reads any pushed-back bytes; after |
| 145 | * that, if fewer than <code>len</code> bytes have been read then it |
| 146 | * reads from the underlying input stream. If <code>len</code> is not zero, the method |
| 147 | * blocks until at least 1 byte of input is available; otherwise, no |
| 148 | * bytes are read and <code>0</code> is returned. |
| 149 | * |
| 150 | * @param b the buffer into which the data is read. |
| 151 | * @param off the start offset in the destination array <code>b</code> |
| 152 | * @param len the maximum number of bytes read. |
| 153 | * @return the total number of bytes read into the buffer, or |
| 154 | * <code>-1</code> if there is no more data because the end of |
| 155 | * the stream has been reached. |
| 156 | * @exception NullPointerException If <code>b</code> is <code>null</code>. |
| 157 | * @exception IndexOutOfBoundsException If <code>off</code> is negative, |
| 158 | * <code>len</code> is negative, or <code>len</code> is greater than |
| 159 | * <code>b.length - off</code> |
| 160 | * @exception IOException if this input stream has been closed by |
| 161 | * invoking its {@link #close()} method, |
| 162 | * or an I/O error occurs. |
| 163 | * @see java.io.InputStream#read(byte[], int, int) |
| 164 | */ |
| 165 | public int read(byte[] b, int off, int len) throws IOException { |
| 166 | ensureOpen(); |
| 167 | if (b == null) { |
| 168 | throw new NullPointerException(); |
| 169 | } else if (off < 0 || len < 0 || len > b.length - off) { |
| 170 | throw new IndexOutOfBoundsException(); |
| 171 | } else if (len == 0) { |
| 172 | return 0; |
| 173 | } |
| 174 | |
| 175 | int avail = buf.length - pos; |
| 176 | if (avail > 0) { |
| 177 | if (len < avail) { |
| 178 | avail = len; |
| 179 | } |
| 180 | System.arraycopy(buf, pos, b, off, avail); |
| 181 | pos += avail; |
| 182 | off += avail; |
| 183 | len -= avail; |
| 184 | } |
| 185 | if (len > 0) { |
| 186 | len = super.read(b, off, len); |
| 187 | if (len == -1) { |
| 188 | return avail == 0 ? -1 : avail; |
| 189 | } |
| 190 | return avail + len; |
| 191 | } |
| 192 | return avail; |
| 193 | } |
| 194 | |
| 195 | /** |
| 196 | * Pushes back a byte by copying it to the front of the pushback buffer. |
| 197 | * After this method returns, the next byte to be read will have the value |
| 198 | * <code>(byte)b</code>. |
| 199 | * |
| 200 | * @param b the <code>int</code> value whose low-order |
| 201 | * byte is to be pushed back. |
| 202 | * @exception IOException If there is not enough room in the pushback |
| 203 | * buffer for the byte, or this input stream has been closed by |
| 204 | * invoking its {@link #close()} method. |
| 205 | */ |
| 206 | public void unread(int b) throws IOException { |
| 207 | ensureOpen(); |
| 208 | if (pos == 0) { |
| 209 | throw new IOException("Push back buffer is full"); |
| 210 | } |
| 211 | buf[--pos] = (byte)b; |
| 212 | } |
| 213 | |
| 214 | /** |
| 215 | * Pushes back a portion of an array of bytes by copying it to the front |
| 216 | * of the pushback buffer. After this method returns, the next byte to be |
| 217 | * read will have the value <code>b[off]</code>, the byte after that will |
| 218 | * have the value <code>b[off+1]</code>, and so forth. |
| 219 | * |
| 220 | * @param b the byte array to push back. |
| 221 | * @param off the start offset of the data. |
| 222 | * @param len the number of bytes to push back. |
| 223 | * @exception IOException If there is not enough room in the pushback |
| 224 | * buffer for the specified number of bytes, |
| 225 | * or this input stream has been closed by |
| 226 | * invoking its {@link #close()} method. |
| 227 | * @since JDK1.1 |
| 228 | */ |
| 229 | public void unread(byte[] b, int off, int len) throws IOException { |
| 230 | ensureOpen(); |
| 231 | if (len > pos) { |
| 232 | throw new IOException("Push back buffer is full"); |
| 233 | } |
| 234 | pos -= len; |
| 235 | System.arraycopy(b, off, buf, pos, len); |
| 236 | } |
| 237 | |
| 238 | /** |
| 239 | * Pushes back an array of bytes by copying it to the front of the |
| 240 | * pushback buffer. After this method returns, the next byte to be read |
| 241 | * will have the value <code>b[0]</code>, the byte after that will have the |
| 242 | * value <code>b[1]</code>, and so forth. |
| 243 | * |
| 244 | * @param b the byte array to push back |
| 245 | * @exception IOException If there is not enough room in the pushback |
| 246 | * buffer for the specified number of bytes, |
| 247 | * or this input stream has been closed by |
| 248 | * invoking its {@link #close()} method. |
| 249 | * @since JDK1.1 |
| 250 | */ |
| 251 | public void unread(byte[] b) throws IOException { |
| 252 | unread(b, 0, b.length); |
| 253 | } |
| 254 | |
| 255 | /** |
| 256 | * Returns an estimate of the number of bytes that can be read (or |
| 257 | * skipped over) from this input stream without blocking by the next |
| 258 | * invocation of a method for this input stream. The next invocation might be |
| 259 | * the same thread or another thread. A single read or skip of this |
| 260 | * many bytes will not block, but may read or skip fewer bytes. |
| 261 | * |
| 262 | * <p> The method returns the sum of the number of bytes that have been |
| 263 | * pushed back and the value returned by {@link |
| 264 | * java.io.FilterInputStream#available available}. |
| 265 | * |
| 266 | * @return the number of bytes that can be read (or skipped over) from |
| 267 | * the input stream without blocking. |
| 268 | * @exception IOException if this input stream has been closed by |
| 269 | * invoking its {@link #close()} method, |
| 270 | * or an I/O error occurs. |
| 271 | * @see java.io.FilterInputStream#in |
| 272 | * @see java.io.InputStream#available() |
| 273 | */ |
| 274 | public int available() throws IOException { |
| 275 | ensureOpen(); |
| 276 | return (buf.length - pos) + super.available(); |
| 277 | } |
| 278 | |
| 279 | /** |
| 280 | * Skips over and discards <code>n</code> bytes of data from this |
| 281 | * input stream. The <code>skip</code> method may, for a variety of |
| 282 | * reasons, end up skipping over some smaller number of bytes, |
| 283 | * possibly zero. If <code>n</code> is negative, no bytes are skipped. |
| 284 | * |
| 285 | * <p> The <code>skip</code> method of <code>PushbackInputStream</code> |
| 286 | * first skips over the bytes in the pushback buffer, if any. It then |
| 287 | * calls the <code>skip</code> method of the underlying input stream if |
| 288 | * more bytes need to be skipped. The actual number of bytes skipped |
| 289 | * is returned. |
| 290 | * |
| 291 | * @param n {@inheritDoc} |
| 292 | * @return {@inheritDoc} |
| 293 | * @exception IOException if the stream does not support seek, |
| 294 | * or the stream has been closed by |
| 295 | * invoking its {@link #close()} method, |
| 296 | * or an I/O error occurs. |
| 297 | * @see java.io.FilterInputStream#in |
| 298 | * @see java.io.InputStream#skip(long n) |
| 299 | * @since 1.2 |
| 300 | */ |
| 301 | public long skip(long n) throws IOException { |
| 302 | ensureOpen(); |
| 303 | if (n <= 0) { |
| 304 | return 0; |
| 305 | } |
| 306 | |
| 307 | long pskip = buf.length - pos; |
| 308 | if (pskip > 0) { |
| 309 | if (n < pskip) { |
| 310 | pskip = n; |
| 311 | } |
| 312 | pos += pskip; |
| 313 | n -= pskip; |
| 314 | } |
| 315 | if (n > 0) { |
| 316 | pskip += super.skip(n); |
| 317 | } |
| 318 | return pskip; |
| 319 | } |
| 320 | |
| 321 | /** |
| 322 | * Tests if this input stream supports the <code>mark</code> and |
| 323 | * <code>reset</code> methods, which it does not. |
| 324 | * |
| 325 | * @return <code>false</code>, since this class does not support the |
| 326 | * <code>mark</code> and <code>reset</code> methods. |
| 327 | * @see java.io.InputStream#mark(int) |
| 328 | * @see java.io.InputStream#reset() |
| 329 | */ |
| 330 | public boolean markSupported() { |
| 331 | return false; |
| 332 | } |
| 333 | |
| 334 | /** |
| 335 | * Marks the current position in this input stream. |
| 336 | * |
| 337 | * <p> The <code>mark</code> method of <code>PushbackInputStream</code> |
| 338 | * does nothing. |
| 339 | * |
| 340 | * @param readlimit the maximum limit of bytes that can be read before |
| 341 | * the mark position becomes invalid. |
| 342 | * @see java.io.InputStream#reset() |
| 343 | */ |
| 344 | public synchronized void mark(int readlimit) { |
| 345 | } |
| 346 | |
| 347 | /** |
| 348 | * Repositions this stream to the position at the time the |
| 349 | * <code>mark</code> method was last called on this input stream. |
| 350 | * |
| 351 | * <p> The method <code>reset</code> for class |
| 352 | * <code>PushbackInputStream</code> does nothing except throw an |
| 353 | * <code>IOException</code>. |
| 354 | * |
| 355 | * @exception IOException if this method is invoked. |
| 356 | * @see java.io.InputStream#mark(int) |
| 357 | * @see java.io.IOException |
| 358 | */ |
| 359 | public synchronized void reset() throws IOException { |
| 360 | throw new IOException("mark/reset not supported"); |
| 361 | } |
| 362 | |
| 363 | /** |
| 364 | * Closes this input stream and releases any system resources |
| 365 | * associated with the stream. |
| 366 | * Once the stream has been closed, further read(), unread(), |
| 367 | * available(), reset(), or skip() invocations will throw an IOException. |
| 368 | * Closing a previously closed stream has no effect. |
| 369 | * |
| 370 | * @exception IOException if an I/O error occurs. |
| 371 | */ |
| 372 | public synchronized void close() throws IOException { |
| 373 | if (in == null) |
| 374 | return; |
| 375 | in.close(); |
| 376 | in = null; |
| 377 | buf = null; |
| 378 | } |
| 379 | } |