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 | * This abstract class is the superclass of all classes representing |
| 30 | * an input stream of bytes. |
| 31 | * |
| 32 | * <p> Applications that need to define a subclass of <code>InputStream</code> |
| 33 | * must always provide a method that returns the next byte of input. |
| 34 | * |
| 35 | * @author Arthur van Hoff |
| 36 | * @see java.io.BufferedInputStream |
| 37 | * @see java.io.ByteArrayInputStream |
| 38 | * @see java.io.DataInputStream |
| 39 | * @see java.io.FilterInputStream |
| 40 | * @see java.io.InputStream#read() |
| 41 | * @see java.io.OutputStream |
| 42 | * @see java.io.PushbackInputStream |
| 43 | * @since JDK1.0 |
| 44 | */ |
| 45 | public abstract class InputStream implements Closeable { |
| 46 | |
| 47 | // SKIP_BUFFER_SIZE is used to determine the size of skipBuffer |
| 48 | private static final int SKIP_BUFFER_SIZE = 2048; |
| 49 | // skipBuffer is initialized in skip(long), if needed. |
| 50 | private static byte[] skipBuffer; |
| 51 | |
| 52 | /** |
| 53 | * Reads the next byte of data from the input stream. The value byte is |
| 54 | * returned as an <code>int</code> in the range <code>0</code> to |
| 55 | * <code>255</code>. If no byte is available because the end of the stream |
| 56 | * has been reached, the value <code>-1</code> is returned. This method |
| 57 | * blocks until input data is available, the end of the stream is detected, |
| 58 | * or an exception is thrown. |
| 59 | * |
| 60 | * <p> A subclass must provide an implementation of this method. |
| 61 | * |
| 62 | * @return the next byte of data, or <code>-1</code> if the end of the |
| 63 | * stream is reached. |
| 64 | * @exception IOException if an I/O error occurs. |
| 65 | */ |
| 66 | public abstract int read() throws IOException; |
| 67 | |
| 68 | /** |
| 69 | * Reads some number of bytes from the input stream and stores them into |
| 70 | * the buffer array <code>b</code>. The number of bytes actually read is |
| 71 | * returned as an integer. This method blocks until input data is |
| 72 | * available, end of file is detected, or an exception is thrown. |
| 73 | * |
| 74 | * <p> If the length of <code>b</code> is zero, then no bytes are read and |
| 75 | * <code>0</code> is returned; otherwise, there is an attempt to read at |
| 76 | * least one byte. If no byte is available because the stream is at the |
| 77 | * end of the file, the value <code>-1</code> is returned; otherwise, at |
| 78 | * least one byte is read and stored into <code>b</code>. |
| 79 | * |
| 80 | * <p> The first byte read is stored into element <code>b[0]</code>, the |
| 81 | * next one into <code>b[1]</code>, and so on. The number of bytes read is, |
| 82 | * at most, equal to the length of <code>b</code>. Let <i>k</i> be the |
| 83 | * number of bytes actually read; these bytes will be stored in elements |
| 84 | * <code>b[0]</code> through <code>b[</code><i>k</i><code>-1]</code>, |
| 85 | * leaving elements <code>b[</code><i>k</i><code>]</code> through |
| 86 | * <code>b[b.length-1]</code> unaffected. |
| 87 | * |
| 88 | * <p> The <code>read(b)</code> method for class <code>InputStream</code> |
| 89 | * has the same effect as: <pre><code> read(b, 0, b.length) </code></pre> |
| 90 | * |
| 91 | * @param b the buffer into which the data is read. |
| 92 | * @return the total number of bytes read into the buffer, or |
| 93 | * <code>-1</code> is there is no more data because the end of |
| 94 | * the stream has been reached. |
| 95 | * @exception IOException If the first byte cannot be read for any reason |
| 96 | * other than the end of the file, if the input stream has been closed, or |
| 97 | * if some other I/O error occurs. |
| 98 | * @exception NullPointerException if <code>b</code> is <code>null</code>. |
| 99 | * @see java.io.InputStream#read(byte[], int, int) |
| 100 | */ |
| 101 | public int read(byte b[]) throws IOException { |
| 102 | return read(b, 0, b.length); |
| 103 | } |
| 104 | |
| 105 | /** |
| 106 | * Reads up to <code>len</code> bytes of data from the input stream into |
| 107 | * an array of bytes. An attempt is made to read as many as |
| 108 | * <code>len</code> bytes, but a smaller number may be read. |
| 109 | * The number of bytes actually read is returned as an integer. |
| 110 | * |
| 111 | * <p> This method blocks until input data is available, end of file is |
| 112 | * detected, or an exception is thrown. |
| 113 | * |
| 114 | * <p> If <code>len</code> is zero, then no bytes are read and |
| 115 | * <code>0</code> is returned; otherwise, there is an attempt to read at |
| 116 | * least one byte. If no byte is available because the stream is at end of |
| 117 | * file, the value <code>-1</code> is returned; otherwise, at least one |
| 118 | * byte is read and stored into <code>b</code>. |
| 119 | * |
| 120 | * <p> The first byte read is stored into element <code>b[off]</code>, the |
| 121 | * next one into <code>b[off+1]</code>, and so on. The number of bytes read |
| 122 | * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of |
| 123 | * bytes actually read; these bytes will be stored in elements |
| 124 | * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>, |
| 125 | * leaving elements <code>b[off+</code><i>k</i><code>]</code> through |
| 126 | * <code>b[off+len-1]</code> unaffected. |
| 127 | * |
| 128 | * <p> In every case, elements <code>b[0]</code> through |
| 129 | * <code>b[off]</code> and elements <code>b[off+len]</code> through |
| 130 | * <code>b[b.length-1]</code> are unaffected. |
| 131 | * |
| 132 | * <p> The <code>read(b,</code> <code>off,</code> <code>len)</code> method |
| 133 | * for class <code>InputStream</code> simply calls the method |
| 134 | * <code>read()</code> repeatedly. If the first such call results in an |
| 135 | * <code>IOException</code>, that exception is returned from the call to |
| 136 | * the <code>read(b,</code> <code>off,</code> <code>len)</code> method. If |
| 137 | * any subsequent call to <code>read()</code> results in a |
| 138 | * <code>IOException</code>, the exception is caught and treated as if it |
| 139 | * were end of file; the bytes read up to that point are stored into |
| 140 | * <code>b</code> and the number of bytes read before the exception |
| 141 | * occurred is returned. The default implementation of this method blocks |
| 142 | * until the requested amount of input data <code>len</code> has been read, |
| 143 | * end of file is detected, or an exception is thrown. Subclasses are encouraged |
| 144 | * to provide a more efficient implementation of this method. |
| 145 | * |
| 146 | * @param b the buffer into which the data is read. |
| 147 | * @param off the start offset in array <code>b</code> |
| 148 | * at which the data is written. |
| 149 | * @param len the maximum number of bytes to read. |
| 150 | * @return the total number of bytes read into the buffer, or |
| 151 | * <code>-1</code> if there is no more data because the end of |
| 152 | * the stream has been reached. |
| 153 | * @exception IOException If the first byte cannot be read for any reason |
| 154 | * other than end of file, or if the input stream has been closed, or if |
| 155 | * some other I/O error occurs. |
| 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 | * @see java.io.InputStream#read() |
| 161 | */ |
| 162 | public int read(byte b[], int off, int len) throws IOException { |
| 163 | if (b == null) { |
| 164 | throw new NullPointerException(); |
| 165 | } else if (off < 0 || len < 0 || len > b.length - off) { |
| 166 | throw new IndexOutOfBoundsException(); |
| 167 | } else if (len == 0) { |
| 168 | return 0; |
| 169 | } |
| 170 | |
| 171 | int c = read(); |
| 172 | if (c == -1) { |
| 173 | return -1; |
| 174 | } |
| 175 | b[off] = (byte)c; |
| 176 | |
| 177 | int i = 1; |
| 178 | try { |
| 179 | for (; i < len ; i++) { |
| 180 | c = read(); |
| 181 | if (c == -1) { |
| 182 | break; |
| 183 | } |
| 184 | b[off + i] = (byte)c; |
| 185 | } |
| 186 | } catch (IOException ee) { |
| 187 | } |
| 188 | return i; |
| 189 | } |
| 190 | |
| 191 | /** |
| 192 | * Skips over and discards <code>n</code> bytes of data from this input |
| 193 | * stream. The <code>skip</code> method may, for a variety of reasons, end |
| 194 | * up skipping over some smaller number of bytes, possibly <code>0</code>. |
| 195 | * This may result from any of a number of conditions; reaching end of file |
| 196 | * before <code>n</code> bytes have been skipped is only one possibility. |
| 197 | * The actual number of bytes skipped is returned. If <code>n</code> is |
| 198 | * negative, no bytes are skipped. |
| 199 | * |
| 200 | * <p> The <code>skip</code> method of this class creates a |
| 201 | * byte array and then repeatedly reads into it until <code>n</code> bytes |
| 202 | * have been read or the end of the stream has been reached. Subclasses are |
| 203 | * encouraged to provide a more efficient implementation of this method. |
| 204 | * For instance, the implementation may depend on the ability to seek. |
| 205 | * |
| 206 | * @param n the number of bytes to be skipped. |
| 207 | * @return the actual number of bytes skipped. |
| 208 | * @exception IOException if the stream does not support seek, |
| 209 | * or if some other I/O error occurs. |
| 210 | */ |
| 211 | public long skip(long n) throws IOException { |
| 212 | |
| 213 | long remaining = n; |
| 214 | int nr; |
| 215 | if (skipBuffer == null) |
| 216 | skipBuffer = new byte[SKIP_BUFFER_SIZE]; |
| 217 | |
| 218 | byte[] localSkipBuffer = skipBuffer; |
| 219 | |
| 220 | if (n <= 0) { |
| 221 | return 0; |
| 222 | } |
| 223 | |
| 224 | while (remaining > 0) { |
| 225 | nr = read(localSkipBuffer, 0, |
| 226 | (int) Math.min(SKIP_BUFFER_SIZE, remaining)); |
| 227 | if (nr < 0) { |
| 228 | break; |
| 229 | } |
| 230 | remaining -= nr; |
| 231 | } |
| 232 | |
| 233 | return n - remaining; |
| 234 | } |
| 235 | |
| 236 | /** |
| 237 | * Returns an estimate of the number of bytes that can be read (or |
| 238 | * skipped over) from this input stream without blocking by the next |
| 239 | * invocation of a method for this input stream. The next invocation |
| 240 | * might be the same thread or another thread. A single read or skip of this |
| 241 | * many bytes will not block, but may read or skip fewer bytes. |
| 242 | * |
| 243 | * <p> Note that while some implementations of {@code InputStream} will return |
| 244 | * the total number of bytes in the stream, many will not. It is |
| 245 | * never correct to use the return value of this method to allocate |
| 246 | * a buffer intended to hold all data in this stream. |
| 247 | * |
| 248 | * <p> A subclass' implementation of this method may choose to throw an |
| 249 | * {@link IOException} if this input stream has been closed by |
| 250 | * invoking the {@link #close()} method. |
| 251 | * |
| 252 | * <p> The {@code available} method for class {@code InputStream} always |
| 253 | * returns {@code 0}. |
| 254 | * |
| 255 | * <p> This method should be overridden by subclasses. |
| 256 | * |
| 257 | * @return an estimate of the number of bytes that can be read (or skipped |
| 258 | * over) from this input stream without blocking or {@code 0} when |
| 259 | * it reaches the end of the input stream. |
| 260 | * @exception IOException if an I/O error occurs. |
| 261 | */ |
| 262 | public int available() throws IOException { |
| 263 | return 0; |
| 264 | } |
| 265 | |
| 266 | /** |
| 267 | * Closes this input stream and releases any system resources associated |
| 268 | * with the stream. |
| 269 | * |
| 270 | * <p> The <code>close</code> method of <code>InputStream</code> does |
| 271 | * nothing. |
| 272 | * |
| 273 | * @exception IOException if an I/O error occurs. |
| 274 | */ |
| 275 | public void close() throws IOException {} |
| 276 | |
| 277 | /** |
| 278 | * Marks the current position in this input stream. A subsequent call to |
| 279 | * the <code>reset</code> method repositions this stream at the last marked |
| 280 | * position so that subsequent reads re-read the same bytes. |
| 281 | * |
| 282 | * <p> The <code>readlimit</code> arguments tells this input stream to |
| 283 | * allow that many bytes to be read before the mark position gets |
| 284 | * invalidated. |
| 285 | * |
| 286 | * <p> The general contract of <code>mark</code> is that, if the method |
| 287 | * <code>markSupported</code> returns <code>true</code>, the stream somehow |
| 288 | * remembers all the bytes read after the call to <code>mark</code> and |
| 289 | * stands ready to supply those same bytes again if and whenever the method |
| 290 | * <code>reset</code> is called. However, the stream is not required to |
| 291 | * remember any data at all if more than <code>readlimit</code> bytes are |
| 292 | * read from the stream before <code>reset</code> is called. |
| 293 | * |
| 294 | * <p> Marking a closed stream should not have any effect on the stream. |
| 295 | * |
| 296 | * <p> The <code>mark</code> method of <code>InputStream</code> does |
| 297 | * nothing. |
| 298 | * |
| 299 | * @param readlimit the maximum limit of bytes that can be read before |
| 300 | * the mark position becomes invalid. |
| 301 | * @see java.io.InputStream#reset() |
| 302 | */ |
| 303 | public synchronized void mark(int readlimit) {} |
| 304 | |
| 305 | /** |
| 306 | * Repositions this stream to the position at the time the |
| 307 | * <code>mark</code> method was last called on this input stream. |
| 308 | * |
| 309 | * <p> The general contract of <code>reset</code> is: |
| 310 | * |
| 311 | * <p><ul> |
| 312 | * |
| 313 | * <li> If the method <code>markSupported</code> returns |
| 314 | * <code>true</code>, then: |
| 315 | * |
| 316 | * <ul><li> If the method <code>mark</code> has not been called since |
| 317 | * the stream was created, or the number of bytes read from the stream |
| 318 | * since <code>mark</code> was last called is larger than the argument |
| 319 | * to <code>mark</code> at that last call, then an |
| 320 | * <code>IOException</code> might be thrown. |
| 321 | * |
| 322 | * <li> If such an <code>IOException</code> is not thrown, then the |
| 323 | * stream is reset to a state such that all the bytes read since the |
| 324 | * most recent call to <code>mark</code> (or since the start of the |
| 325 | * file, if <code>mark</code> has not been called) will be resupplied |
| 326 | * to subsequent callers of the <code>read</code> method, followed by |
| 327 | * any bytes that otherwise would have been the next input data as of |
| 328 | * the time of the call to <code>reset</code>. </ul> |
| 329 | * |
| 330 | * <li> If the method <code>markSupported</code> returns |
| 331 | * <code>false</code>, then: |
| 332 | * |
| 333 | * <ul><li> The call to <code>reset</code> may throw an |
| 334 | * <code>IOException</code>. |
| 335 | * |
| 336 | * <li> If an <code>IOException</code> is not thrown, then the stream |
| 337 | * is reset to a fixed state that depends on the particular type of the |
| 338 | * input stream and how it was created. The bytes that will be supplied |
| 339 | * to subsequent callers of the <code>read</code> method depend on the |
| 340 | * particular type of the input stream. </ul></ul> |
| 341 | * |
| 342 | * <p>The method <code>reset</code> for class <code>InputStream</code> |
| 343 | * does nothing except throw an <code>IOException</code>. |
| 344 | * |
| 345 | * @exception IOException if this stream has not been marked or if the |
| 346 | * mark has been invalidated. |
| 347 | * @see java.io.InputStream#mark(int) |
| 348 | * @see java.io.IOException |
| 349 | */ |
| 350 | public synchronized void reset() throws IOException { |
| 351 | throw new IOException("mark/reset not supported"); |
| 352 | } |
| 353 | |
| 354 | /** |
| 355 | * Tests if this input stream supports the <code>mark</code> and |
| 356 | * <code>reset</code> methods. Whether or not <code>mark</code> and |
| 357 | * <code>reset</code> are supported is an invariant property of a |
| 358 | * particular input stream instance. The <code>markSupported</code> method |
| 359 | * of <code>InputStream</code> returns <code>false</code>. |
| 360 | * |
| 361 | * @return <code>true</code> if this stream instance supports the mark |
| 362 | * and reset methods; <code>false</code> otherwise. |
| 363 | * @see java.io.InputStream#mark(int) |
| 364 | * @see java.io.InputStream#reset() |
| 365 | */ |
| 366 | public boolean markSupported() { |
| 367 | return false; |
| 368 | } |
| 369 | |
| 370 | } |