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 }