001/* InputStream.java -- Base class for input 002 Copyright (C) 1998, 1999, 2001, 2004, 2005 Free Software Foundation, Inc. 003 004This file is part of GNU Classpath. 005 006GNU Classpath is free software; you can redistribute it and/or modify 007it under the terms of the GNU General Public License as published by 008the Free Software Foundation; either version 2, or (at your option) 009any later version. 010 011GNU Classpath is distributed in the hope that it will be useful, but 012WITHOUT ANY WARRANTY; without even the implied warranty of 013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 014General Public License for more details. 015 016You should have received a copy of the GNU General Public License 017along with GNU Classpath; see the file COPYING. If not, write to the 018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 01902110-1301 USA. 020 021Linking this library statically or dynamically with other modules is 022making a combined work based on this library. Thus, the terms and 023conditions of the GNU General Public License cover the whole 024combination. 025 026As a special exception, the copyright holders of this library give you 027permission to link this library with independent modules to produce an 028executable, regardless of the license terms of these independent 029modules, and to copy and distribute the resulting executable under 030terms of your choice, provided that you also meet, for each linked 031independent module, the terms and conditions of the license of that 032module. An independent module is a module which is not derived from 033or based on this library. If you modify this library, you may extend 034this exception to your version of the library, but you are not 035obligated to do so. If you do not wish to do so, delete this 036exception statement from your version. */ 037 038 039package java.io; 040 041/** 042 * This abstract class forms the base of the hierarchy of classes that read 043 * input as a stream of bytes. It provides a common set of methods for 044 * reading bytes from streams. Subclasses implement and extend these 045 * methods to read bytes from a particular input source such as a file 046 * or network connection. 047 * 048 * @author Aaron M. Renn (arenn@urbanophile.com) 049 * @author Warren Levy (warrenl@cygnus.com) 050 */ 051public abstract class InputStream implements Closeable 052{ 053 /** 054 * Default, no-arg, public constructor 055 */ 056 public InputStream() 057 { 058 } 059 060 /** 061 * This method returns the number of bytes that can be read from this 062 * stream before a read can block. A return of 0 indicates that blocking 063 * might (or might not) occur on the very next read attempt. 064 * <p> 065 * This method always returns 0 in this class 066 * 067 * @return The number of bytes that can be read before blocking could occur 068 * 069 * @exception IOException If an error occurs 070 */ 071 public int available() throws IOException 072 { 073 return 0; 074 } 075 076 /** 077 * This method closes the stream. Any futher attempts to read from the 078 * stream may generate an <code>IOException</code> 079 * <p> 080 * This method does nothing in this class, but subclasses may override 081 * this method in order to provide additional functionality. 082 * 083 * @exception IOException If an error occurs, which can only happen 084 * in a subclass 085 */ 086 public void close() throws IOException 087 { 088 // Do nothing 089 } 090 091 /** 092 * This method marks a position in the input to which the stream can 093 * be "reset" by calling the <code>reset()</code> method. The 094 * parameter @code{readlimit} is the number of bytes that can be read 095 * from the stream after setting the mark before the mark becomes 096 * invalid. For example, if <code>mark()</code> is called with a 097 * read limit of 10, then when 11 bytes of data are read from the 098 * stream before the <code>reset()</code> method is called, then the 099 * mark is invalid and the stream object instance is not required to 100 * remember the mark. 101 * <p> 102 * This method does nothing in this class, but subclasses may override it 103 * to provide mark/reset functionality. 104 * 105 * @param readLimit The number of bytes that can be read before the 106 * mark becomes invalid 107 */ 108 public void mark(int readLimit) 109 { 110 // Do nothing 111 } 112 113 /** 114 * This method returns a boolean that indicates whether the mark/reset 115 * methods are supported in this class. Those methods can be used to 116 * remember a specific point in the stream and reset the stream to that 117 * point. 118 * <p> 119 * This method always returns <code>false</code> in this class, but 120 * subclasses can override this method to return <code>true</code> 121 * if they support mark/reset functionality. 122 * 123 * @return <code>true</code> if mark/reset functionality is 124 * supported, <code>false</code> otherwise 125 */ 126 public boolean markSupported() 127 { 128 return false; 129 } 130 131 /** 132 * This method reads an unsigned byte from the input stream and returns it 133 * as an int in the range of 0-255. This method also will return -1 if 134 * the end of the stream has been reached. 135 * <p> 136 * This method will block until the byte can be read. 137 * 138 * @return The byte read or -1 if end of stream 139 * 140 * @exception IOException If an error occurs 141 */ 142 public abstract int read() throws IOException; 143 144 /** 145 * This method reads bytes from a stream and stores them into a caller 146 * supplied buffer. This method attempts to completely fill the buffer, 147 * but can return before doing so. The actual number of bytes read is 148 * returned as an int. A -1 is returned to indicate the end of the stream. 149 * <p> 150 * This method will block until some data can be read. 151 * <p> 152 * This method operates by calling an overloaded read method like so: 153 * <code>read(b, 0, b.length)</code> 154 * 155 * @param b The buffer into which the bytes read will be stored. 156 * 157 * @return The number of bytes read or -1 if end of stream. 158 * 159 * @exception IOException If an error occurs. 160 */ 161 public int read(byte[] b) throws IOException 162 { 163 return read(b, 0, b.length); 164 } 165 166 /** 167 * This method read bytes from a stream and stores them into a 168 * caller supplied buffer. It starts storing the data at index 169 * <code>off</code> into the buffer and attempts to read 170 * <code>len</code> bytes. This method can return before reading the 171 * number of bytes requested. The actual number of bytes read is 172 * returned as an int. A -1 is returned to indicate the end of the 173 * stream. 174 * <p> 175 * This method will block until some data can be read. 176 * <p> 177 * This method operates by calling the single byte <code>read()</code> method 178 * in a loop until the desired number of bytes are read. The read loop 179 * stops short if the end of the stream is encountered or if an IOException 180 * is encountered on any read operation except the first. If the first 181 * attempt to read a bytes fails, the IOException is allowed to propagate 182 * upward. And subsequent IOException is caught and treated identically 183 * to an end of stream condition. Subclasses can (and should if possible) 184 * override this method to provide a more efficient implementation. 185 * 186 * @param b The array into which the bytes read should be stored 187 * @param off The offset into the array to start storing bytes 188 * @param len The requested number of bytes to read 189 * 190 * @return The actual number of bytes read, or -1 if end of stream. 191 * 192 * @exception IOException If an error occurs. 193 */ 194 public int read(byte[] b, int off, int len) throws IOException 195 { 196 if (off < 0 || len < 0 || b.length - off < len) 197 throw new IndexOutOfBoundsException(); 198 199 int i, ch; 200 201 for (i = 0; i < len; ++i) 202 try 203 { 204 if ((ch = read()) < 0) 205 return i == 0 ? -1 : i; // EOF 206 b[off + i] = (byte) ch; 207 } 208 catch (IOException ex) 209 { 210 // Only reading the first byte should cause an IOException. 211 if (i == 0) 212 throw ex; 213 return i; 214 } 215 216 return i; 217 } 218 219 /** 220 * This method resets a stream to the point where the 221 * <code>mark()</code> method was called. Any bytes that were read 222 * after the mark point was set will be re-read during subsequent 223 * reads. 224 * <p> 225 * This method always throws an IOException in this class, but subclasses 226 * can override this method if they provide mark/reset functionality. 227 * 228 * @exception IOException Always thrown for this class 229 */ 230 public void reset() throws IOException 231 { 232 throw new IOException("mark/reset not supported"); 233 } 234 235 /** 236 * This method skips the specified number of bytes in the stream. It 237 * returns the actual number of bytes skipped, which may be less than the 238 * requested amount. 239 * <p> 240 * This method reads and discards bytes into a byte array until the 241 * specified number of bytes were skipped or until either the end of stream 242 * is reached or a read attempt returns a short count. Subclasses can 243 * override this metho to provide a more efficient implementation where 244 * one exists. 245 * 246 * @param n The requested number of bytes to skip 247 * 248 * @return The actual number of bytes skipped. 249 * 250 * @exception IOException If an error occurs 251 */ 252 public long skip(long n) throws IOException 253 { 254 // Throw away n bytes by reading them into a temp byte[]. 255 // Limit the temp array to 2Kb so we don't grab too much memory. 256 final int buflen = n > 2048 ? 2048 : (int) n; 257 byte[] tmpbuf = new byte[buflen]; 258 final long origN = n; 259 260 while (n > 0L) 261 { 262 int numread = read(tmpbuf, 0, n > buflen ? buflen : (int) n); 263 if (numread <= 0) 264 break; 265 n -= numread; 266 } 267 268 return origN - n; 269 } 270}