001/* ByteArrayInputStream.java -- Read an array as a stream 002 Copyright (C) 1998, 1999, 2001, 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 class permits an array of bytes to be read as an input stream. 043 * 044 * @author Warren Levy (warrenl@cygnus.com) 045 * @author Aaron M. Renn (arenn@urbanophile.com) 046 */ 047public class ByteArrayInputStream extends InputStream 048{ 049 /** 050 * The array that contains the data supplied during read operations 051 */ 052 protected byte[] buf; 053 054 /** 055 * The array index of the next byte to be read from the buffer 056 * <code>buf</code> 057 */ 058 protected int pos; 059 060 /** 061 * The currently marked position in the stream. This defaults to 0, so a 062 * reset operation on the stream resets it to read from array index 0 in 063 * the buffer - even if the stream was initially created with an offset 064 * greater than 0 065 */ 066 protected int mark; 067 068 /** 069 * This indicates the maximum number of bytes that can be read from this 070 * stream. It is the array index of the position after the last valid 071 * byte in the buffer <code>buf</code> 072 */ 073 protected int count; 074 075 /** 076 * Create a new ByteArrayInputStream that will read bytes from the passed 077 * in byte array. This stream will read from the beginning to the end 078 * of the array. It is identical to calling an overloaded constructor 079 * as <code>ByteArrayInputStream(buf, 0, buf.length)</code>. 080 * <p> 081 * Note that this array is not copied. If its contents are changed 082 * while this stream is being read, those changes will be reflected in the 083 * bytes supplied to the reader. Please use caution in changing the 084 * contents of the buffer while this stream is open. 085 * 086 * @param buffer The byte array buffer this stream will read from. 087 */ 088 public ByteArrayInputStream(byte[] buffer) 089 { 090 this(buffer, 0, buffer.length); 091 } 092 093 /** 094 * Create a new ByteArrayInputStream that will read bytes from the 095 * passed in byte array. This stream will read from position 096 * <code>offset</code> in the array for a length of 097 * <code>length</code> bytes past <code>offset</code>. If the 098 * stream is reset to a position before <code>offset</code> then 099 * more than <code>length</code> bytes can be read from the stream. 100 * The <code>length</code> value should be viewed as the array index 101 * one greater than the last position in the buffer to read. 102 * <p> 103 * Note that this array is not copied. If its contents are changed 104 * while this stream is being read, those changes will be reflected in the 105 * bytes supplied to the reader. Please use caution in changing the 106 * contents of the buffer while this stream is open. 107 * 108 * @param buffer The byte array buffer this stream will read from. 109 * @param offset The index into the buffer to start reading bytes from 110 * @param length The number of bytes to read from the buffer 111 */ 112 public ByteArrayInputStream(byte[] buffer, int offset, int length) 113 { 114 if (offset < 0 || length < 0 || offset > buffer.length) 115 throw new IllegalArgumentException(); 116 117 buf = buffer; 118 119 count = offset + length; 120 if (count > buf.length) 121 count = buf.length; 122 123 pos = offset; 124 mark = pos; 125 } 126 127 /** 128 * This method returns the number of bytes available to be read from this 129 * stream. The value returned will be equal to <code>count - pos</code>. 130 * 131 * @return The number of bytes that can be read from this stream 132 * before blocking, which is all of them 133 */ 134 public synchronized int available() 135 { 136 return count - pos; 137 } 138 139 /** 140 * This method sets the mark position in this stream to the current 141 * position. Note that the <code>readlimit</code> parameter in this 142 * method does nothing as this stream is always capable of 143 * remembering all the bytes int it. 144 * <p> 145 * Note that in this class the mark position is set by default to 146 * position 0 in the stream. This is in constrast to some other 147 * stream types where there is no default mark position. 148 * 149 * @param readLimit The number of bytes this stream must remember. 150 * This parameter is ignored. 151 */ 152 public synchronized void mark(int readLimit) 153 { 154 // readLimit is ignored per Java Class Lib. book, p.220. 155 mark = pos; 156 } 157 158 /** 159 * This method overrides the <code>markSupported</code> method in 160 * <code>InputStream</code> in order to return <code>true</code> - 161 * indicating that this stream class supports mark/reset 162 * functionality. 163 * 164 * @return <code>true</code> to indicate that this class supports 165 * mark/reset. 166 */ 167 public boolean markSupported() 168 { 169 return true; 170 } 171 172 /** 173 * This method reads one byte from the stream. The <code>pos</code> 174 * counter is advanced to the next byte to be read. The byte read is 175 * returned as an int in the range of 0-255. If the stream position 176 * is already at the end of the buffer, no byte is read and a -1 is 177 * returned in order to indicate the end of the stream. 178 * 179 * @return The byte read, or -1 if end of stream 180 */ 181 public synchronized int read() 182 { 183 if (pos < count) 184 return ((int) buf[pos++]) & 0xFF; 185 return -1; 186 } 187 188 /** 189 * This method reads bytes from the stream and stores them into a 190 * caller supplied buffer. It starts storing the data at index 191 * <code>offset</code> into the buffer and attempts to read 192 * <code>len</code> bytes. This method can return before reading 193 * the number of bytes requested if the end of the stream is 194 * encountered first. The actual number of bytes read is returned. 195 * If no bytes can be read because the stream is already at the end 196 * of stream position, a -1 is returned. 197 * <p> 198 * This method does not block. 199 * 200 * @param buffer The array into which the bytes read should be stored. 201 * @param offset The offset into the array to start storing bytes 202 * @param length The requested number of bytes to read 203 * 204 * @return The actual number of bytes read, or -1 if end of stream. 205 */ 206 public synchronized int read(byte[] buffer, int offset, int length) 207 { 208 if (pos >= count) 209 return -1; 210 211 int numBytes = Math.min(count - pos, length); 212 System.arraycopy(buf, pos, buffer, offset, numBytes); 213 pos += numBytes; 214 return numBytes; 215 } 216 217 /** 218 * This method sets the read position in the stream to the mark 219 * point by setting the <code>pos</code> variable equal to the 220 * <code>mark</code> variable. Since a mark can be set anywhere in 221 * the array, the mark/reset methods int this class can be used to 222 * provide random search capabilities for this type of stream. 223 */ 224 public synchronized void reset() 225 { 226 pos = mark; 227 } 228 229 /** 230 * This method attempts to skip the requested number of bytes in the 231 * input stream. It does this by advancing the <code>pos</code> 232 * value by the specified number of bytes. It this would exceed the 233 * length of the buffer, then only enough bytes are skipped to 234 * position the stream at the end of the buffer. The actual number 235 * of bytes skipped is returned. 236 * 237 * @param num The requested number of bytes to skip 238 * 239 * @return The actual number of bytes skipped. 240 */ 241 public synchronized long skip(long num) 242 { 243 // Even though the var numBytes is a long, in reality it can never 244 // be larger than an int since the result of subtracting 2 positive 245 // ints will always fit in an int. Since we have to return a long 246 // anyway, numBytes might as well just be a long. 247 long numBytes = Math.min((long) (count - pos), num < 0 ? 0L : num); 248 pos += numBytes; 249 return numBytes; 250 } 251}