libjava/java/io/ByteArrayInputStream.java

   1 /* ByteArrayInputStream.java -- Read an array as a stream
   2    Copyright (C) 1998, 1999, 2001, 2005  Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package java.io;
  40
  41 /**
  42   * This class permits an array of bytes to be read as an input stream.
  43   *
  44   * @author Warren Levy (warrenl@cygnus.com)
  45   * @author Aaron M. Renn (arenn@urbanophile.com)
  46   */
  47 public class ByteArrayInputStream extends InputStream
  48 {
  49   /**
  50    * The array that contains the data supplied during read operations
  51    */
  52   protected byte[] buf;
  53
  54   /**
  55    * The array index of the next byte to be read from the buffer
  56    * <code>buf</code>
  57    */
  58   protected int pos;
  59
  60   /**
  61    * The currently marked position in the stream.  This defaults to 0, so a
  62    * reset operation on the stream resets it to read from array index 0 in
  63    * the buffer - even if the stream was initially created with an offset
  64    * greater than 0
  65    */
  66   protected int mark;
  67
  68   /**
  69    * This indicates the maximum number of bytes that can be read from this
  70    * stream.  It is the array index of the position after the last valid
  71    * byte in the buffer <code>buf</code>
  72    */
  73   protected int count;
  74
  75   /**
  76    * Create a new ByteArrayInputStream that will read bytes from the passed
  77    * in byte array.  This stream will read from the beginning to the end
  78    * of the array.  It is identical to calling an overloaded constructor
  79    * as <code>ByteArrayInputStream(buf, 0, buf.length)</code>.
  80    * <p>
  81    * Note that this array is not copied.  If its contents are changed
  82    * while this stream is being read, those changes will be reflected in the
  83    * bytes supplied to the reader.  Please use caution in changing the
  84    * contents of the buffer while this stream is open.
  85    *
  86    * @param buffer The byte array buffer this stream will read from.
  87    */
  88   public ByteArrayInputStream(byte[] buffer)
  89   {
  90     this(buffer, 0, buffer.length);
  91   }
  92
  93   /**
  94    * Create a new ByteArrayInputStream that will read bytes from the
  95    * passed in byte array.  This stream will read from position
  96    * <code>offset</code> in the array for a length of
  97    * <code>length</code> bytes past <code>offset</code>.  If the
  98    * stream is reset to a position before <code>offset</code> then
  99    * 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 }