1 /* 2 * Copyright (c) 1994, 2013, 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 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 // MAX_SKIP_BUFFER_SIZE is used to determine the maximum buffer size to 48 // use when skipping. 49 private static final int MAX_SKIP_BUFFER_SIZE = 2048; 50 51 /** 52 * Reads the next byte of data from the input stream. The value byte is 53 * returned as an <code>int</code> in the range <code>0</code> to 54 * <code>255</code>. If no byte is available because the end of the stream 55 * has been reached, the value <code>-1</code> is returned. This method 56 * blocks until input data is available, the end of the stream is detected, 57 * or an exception is thrown. 58 * 59 * <p> A subclass must provide an implementation of this method. 60 * 61 * @return the next byte of data, or <code>-1</code> if the end of the 62 * stream is reached. 63 * @exception IOException if an I/O error occurs. 64 */ read()65 public abstract int read() throws IOException; 66 67 /** 68 * Reads some number of bytes from the input stream and stores them into 69 * the buffer array <code>b</code>. The number of bytes actually read is 70 * returned as an integer. This method blocks until input data is 71 * available, end of file is detected, or an exception is thrown. 72 * 73 * <p> If the length of <code>b</code> is zero, then no bytes are read and 74 * <code>0</code> is returned; otherwise, there is an attempt to read at 75 * least one byte. If no byte is available because the stream is at the 76 * end of the file, the value <code>-1</code> is returned; otherwise, at 77 * least one byte is read and stored into <code>b</code>. 78 * 79 * <p> The first byte read is stored into element <code>b[0]</code>, the 80 * next one into <code>b[1]</code>, and so on. The number of bytes read is, 81 * at most, equal to the length of <code>b</code>. Let <i>k</i> be the 82 * number of bytes actually read; these bytes will be stored in elements 83 * <code>b[0]</code> through <code>b[</code><i>k</i><code>-1]</code>, 84 * leaving elements <code>b[</code><i>k</i><code>]</code> through 85 * <code>b[b.length-1]</code> unaffected. 86 * 87 * <p> The <code>read(b)</code> method for class <code>InputStream</code> 88 * has the same effect as: <pre><code> read(b, 0, b.length) </code></pre> 89 * 90 * @param b the buffer into which the data is read. 91 * @return the total number of bytes read into the buffer, or 92 * <code>-1</code> if there is no more data because the end of 93 * the stream has been reached. 94 * @exception IOException If the first byte cannot be read for any reason 95 * other than the end of the file, if the input stream has been closed, or 96 * if some other I/O error occurs. 97 * @exception NullPointerException if <code>b</code> is <code>null</code>. 98 * @see java.io.InputStream#read(byte[], int, int) 99 */ read(byte b[])100 public int read(byte b[]) throws IOException { 101 return read(b, 0, b.length); 102 } 103 104 /** 105 * Reads up to <code>len</code> bytes of data from the input stream into 106 * an array of bytes. An attempt is made to read as many as 107 * <code>len</code> bytes, but a smaller number may be read. 108 * The number of bytes actually read is returned as an integer. 109 * 110 * <p> This method blocks until input data is available, end of file is 111 * detected, or an exception is thrown. 112 * 113 * <p> If <code>len</code> is zero, then no bytes are read and 114 * <code>0</code> is returned; otherwise, there is an attempt to read at 115 * least one byte. If no byte is available because the stream is at end of 116 * file, the value <code>-1</code> is returned; otherwise, at least one 117 * byte is read and stored into <code>b</code>. 118 * 119 * <p> The first byte read is stored into element <code>b[off]</code>, the 120 * next one into <code>b[off+1]</code>, and so on. The number of bytes read 121 * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of 122 * bytes actually read; these bytes will be stored in elements 123 * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>, 124 * leaving elements <code>b[off+</code><i>k</i><code>]</code> through 125 * <code>b[off+len-1]</code> unaffected. 126 * 127 * <p> In every case, elements <code>b[0]</code> through 128 * <code>b[off]</code> and elements <code>b[off+len]</code> through 129 * <code>b[b.length-1]</code> are unaffected. 130 * 131 * <p> The <code>read(b,</code> <code>off,</code> <code>len)</code> method 132 * for class <code>InputStream</code> simply calls the method 133 * <code>read()</code> repeatedly. If the first such call results in an 134 * <code>IOException</code>, that exception is returned from the call to 135 * the <code>read(b,</code> <code>off,</code> <code>len)</code> method. If 136 * any subsequent call to <code>read()</code> results in a 137 * <code>IOException</code>, the exception is caught and treated as if it 138 * were end of file; the bytes read up to that point are stored into 139 * <code>b</code> and the number of bytes read before the exception 140 * occurred is returned. The default implementation of this method blocks 141 * until the requested amount of input data <code>len</code> has been read, 142 * end of file is detected, or an exception is thrown. Subclasses are encouraged 143 * to provide a more efficient implementation of this method. 144 * 145 * @param b the buffer into which the data is read. 146 * @param off the start offset in array <code>b</code> 147 * at which the data is written. 148 * @param len the maximum number of bytes to read. 149 * @return the total number of bytes read into the buffer, or 150 * <code>-1</code> if there is no more data because the end of 151 * the stream has been reached. 152 * @exception IOException If the first byte cannot be read for any reason 153 * other than end of file, or if the input stream has been closed, or if 154 * some other I/O error occurs. 155 * @exception NullPointerException If <code>b</code> is <code>null</code>. 156 * @exception IndexOutOfBoundsException If <code>off</code> is negative, 157 * <code>len</code> is negative, or <code>len</code> is greater than 158 * <code>b.length - off</code> 159 * @see java.io.InputStream#read() 160 */ read(byte b[], int off, int len)161 public int read(byte b[], int off, int len) throws IOException { 162 if (b == null) { 163 throw new NullPointerException(); 164 } else if (off < 0 || len < 0 || len > b.length - off) { 165 throw new IndexOutOfBoundsException(); 166 } else if (len == 0) { 167 return 0; 168 } 169 170 int c = read(); 171 if (c == -1) { 172 return -1; 173 } 174 b[off] = (byte)c; 175 176 int i = 1; 177 try { 178 for (; i < len ; i++) { 179 c = read(); 180 if (c == -1) { 181 break; 182 } 183 b[off + i] = (byte)c; 184 } 185 } catch (IOException ee) { 186 } 187 return i; 188 } 189 190 /** 191 * Skips over and discards <code>n</code> bytes of data from this input 192 * stream. The <code>skip</code> method may, for a variety of reasons, end 193 * up skipping over some smaller number of bytes, possibly <code>0</code>. 194 * This may result from any of a number of conditions; reaching end of file 195 * before <code>n</code> bytes have been skipped is only one possibility. 196 * The actual number of bytes skipped is returned. If {@code n} is 197 * negative, the {@code skip} method for class {@code InputStream} always 198 * returns 0, and no bytes are skipped. Subclasses may handle the negative 199 * value differently. 200 * 201 * <p> The <code>skip</code> method of this class creates a 202 * byte array and then repeatedly reads into it until <code>n</code> bytes 203 * have been read or the end of the stream has been reached. Subclasses are 204 * encouraged to provide a more efficient implementation of this method. 205 * For instance, the implementation may depend on the ability to seek. 206 * 207 * @param n the number of bytes to be skipped. 208 * @return the actual number of bytes skipped. 209 * @exception IOException if the stream does not support seek, 210 * or if some other I/O error occurs. 211 */ skip(long n)212 public long skip(long n) throws IOException { 213 214 long remaining = n; 215 int nr; 216 217 if (n <= 0) { 218 return 0; 219 } 220 221 int size = (int)Math.min(MAX_SKIP_BUFFER_SIZE, remaining); 222 byte[] skipBuffer = new byte[size]; 223 while (remaining > 0) { 224 nr = read(skipBuffer, 0, (int)Math.min(size, remaining)); 225 if (nr < 0) { 226 break; 227 } 228 remaining -= nr; 229 } 230 231 return n - remaining; 232 } 233 234 /** 235 * Returns an estimate of the number of bytes that can be read (or 236 * skipped over) from this input stream without blocking by the next 237 * invocation of a method for this input stream. The next invocation 238 * might be the same thread or another thread. A single read or skip of this 239 * many bytes will not block, but may read or skip fewer bytes. 240 * 241 * <p> Note that while some implementations of {@code InputStream} will return 242 * the total number of bytes in the stream, many will not. It is 243 * never correct to use the return value of this method to allocate 244 * a buffer intended to hold all data in this stream. 245 * 246 * <p> A subclass' implementation of this method may choose to throw an 247 * {@link IOException} if this input stream has been closed by 248 * invoking the {@link #close()} method. 249 * 250 * <p> The {@code available} method for class {@code InputStream} always 251 * returns {@code 0}. 252 * 253 * <p> This method should be overridden by subclasses. 254 * 255 * @return an estimate of the number of bytes that can be read (or skipped 256 * over) from this input stream without blocking or {@code 0} when 257 * it reaches the end of the input stream. 258 * @exception IOException if an I/O error occurs. 259 */ available()260 public int available() throws IOException { 261 return 0; 262 } 263 264 /** 265 * Closes this input stream and releases any system resources associated 266 * with the stream. 267 * 268 * <p> The <code>close</code> method of <code>InputStream</code> does 269 * nothing. 270 * 271 * @exception IOException if an I/O error occurs. 272 */ close()273 public void close() throws IOException {} 274 275 /** 276 * Marks the current position in this input stream. A subsequent call to 277 * the <code>reset</code> method repositions this stream at the last marked 278 * position so that subsequent reads re-read the same bytes. 279 * 280 * <p> The <code>readlimit</code> arguments tells this input stream to 281 * allow that many bytes to be read before the mark position gets 282 * invalidated. 283 * 284 * <p> The general contract of <code>mark</code> is that, if the method 285 * <code>markSupported</code> returns <code>true</code>, the stream somehow 286 * remembers all the bytes read after the call to <code>mark</code> and 287 * stands ready to supply those same bytes again if and whenever the method 288 * <code>reset</code> is called. However, the stream is not required to 289 * remember any data at all if more than <code>readlimit</code> bytes are 290 * read from the stream before <code>reset</code> is called. 291 * 292 * <p> Marking a closed stream should not have any effect on the stream. 293 * 294 * <p> The <code>mark</code> method of <code>InputStream</code> does 295 * nothing. 296 * 297 * @param readlimit the maximum limit of bytes that can be read before 298 * the mark position becomes invalid. 299 * @see java.io.InputStream#reset() 300 */ mark(int readlimit)301 public synchronized void mark(int readlimit) {} 302 303 /** 304 * Repositions this stream to the position at the time the 305 * <code>mark</code> method was last called on this input stream. 306 * 307 * <p> The general contract of <code>reset</code> is: 308 * 309 * <ul> 310 * <li> If the method <code>markSupported</code> returns 311 * <code>true</code>, then: 312 * 313 * <ul><li> If the method <code>mark</code> has not been called since 314 * the stream was created, or the number of bytes read from the stream 315 * since <code>mark</code> was last called is larger than the argument 316 * to <code>mark</code> at that last call, then an 317 * <code>IOException</code> might be thrown. 318 * 319 * <li> If such an <code>IOException</code> is not thrown, then the 320 * stream is reset to a state such that all the bytes read since the 321 * most recent call to <code>mark</code> (or since the start of the 322 * file, if <code>mark</code> has not been called) will be resupplied 323 * to subsequent callers of the <code>read</code> method, followed by 324 * any bytes that otherwise would have been the next input data as of 325 * the time of the call to <code>reset</code>. </ul> 326 * 327 * <li> If the method <code>markSupported</code> returns 328 * <code>false</code>, then: 329 * 330 * <ul><li> The call to <code>reset</code> may throw an 331 * <code>IOException</code>. 332 * 333 * <li> If an <code>IOException</code> is not thrown, then the stream 334 * is reset to a fixed state that depends on the particular type of the 335 * input stream and how it was created. The bytes that will be supplied 336 * to subsequent callers of the <code>read</code> method depend on the 337 * particular type of the input stream. </ul></ul> 338 * 339 * <p>The method <code>reset</code> for class <code>InputStream</code> 340 * does nothing except throw an <code>IOException</code>. 341 * 342 * @exception IOException if this stream has not been marked or if the 343 * mark has been invalidated. 344 * @see java.io.InputStream#mark(int) 345 * @see java.io.IOException 346 */ reset()347 public synchronized void reset() throws IOException { 348 throw new IOException("mark/reset not supported"); 349 } 350 351 /** 352 * Tests if this input stream supports the <code>mark</code> and 353 * <code>reset</code> methods. Whether or not <code>mark</code> and 354 * <code>reset</code> are supported is an invariant property of a 355 * particular input stream instance. The <code>markSupported</code> method 356 * of <code>InputStream</code> returns <code>false</code>. 357 * 358 * @return <code>true</code> if this stream instance supports the mark 359 * and reset methods; <code>false</code> otherwise. 360 * @see java.io.InputStream#mark(int) 361 * @see java.io.InputStream#reset() 362 */ markSupported()363 public boolean markSupported() { 364 return false; 365 } 366 367 } 368