libjava/java/io/InputStream.java

   1 /* InputStream.java -- Base class for input
   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 abstract class forms the base of the hierarchy of classes that read
  43   * input as a stream of bytes.  It provides a common set of methods for
  44   * reading bytes from streams.  Subclasses implement and extend these
  45   * methods to read bytes from a particular input source such as a file
  46   * or network connection.
  47   *
  48   * @author Aaron M. Renn (arenn@urbanophile.com)
  49   * @author Warren Levy (warrenl@cygnus.com)
  50   */
  51 public abstract class InputStream
  52 {
  53   /**
  54    * Default, no-arg, public constructor
  55    */
  56   public InputStream()
  57   {
  58   }
  59
  60   /**
  61    * This method returns the number of bytes that can be read from this
  62    * stream before a read can block.  A return of 0 indicates that blocking
  63    * might (or might not) occur on the very next read attempt.
  64    * <p>
  65    * This method always returns 0 in this class
  66    *
  67    * @return The number of bytes that can be read before blocking could occur
  68    *
  69    * @exception IOException If an error occurs
  70    */
  71   public int available() throws IOException
  72   {
  73     return 0;
  74   }
  75
  76   /**
  77    * This method closes the stream.  Any futher attempts to read from the
  78    * stream may generate an <code>IOException</code>
  79    * <p>
  80    * This method does nothing in this class, but subclasses may override
  81    * this method in order to provide additional functionality.
  82    *
  83    * @exception IOException If an error occurs, which can only happen
  84    * in a subclass
  85    */
  86   public void close() throws IOException
  87   {
  88     // Do nothing
  89   }
  90
  91   /**
  92    * This method marks a position in the input to which the stream can
  93    * be "reset" by calling the <code>reset()</code> method.  The
  94    * parameter @code{readlimit} is the number of bytes that can be read
  95    * from the stream after setting the mark before the mark becomes
  96    * invalid.  For example, if <code>mark()</code> is called with a
  97    * read limit of 10, then when 11 bytes of data are read from the
  98    * stream before the <code>reset()</code> method is called, then the
  99    * 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 || off + len > b.length)
 197       throw new IndexOutOfBoundsException();
 198     if (b.length == 0)
 199       return 0;
 200
 201     int i, ch;
 202
 203     for (i = 0; i < len; ++i)
 204       try
 205         {
 206           if ((ch = read()) < 0)
 207             return i == 0 ? -1 : i;             // EOF
 208           b[off + i] = (byte) ch;
 209         }
 210       catch (IOException ex)
 211         {
 212           // Only reading the first byte should cause an IOException.
 213           if (i == 0)
 214             throw ex;
 215           return i;
 216         }
 217
 218     return i;
 219   }
 220
 221   /**
 222    * This method resets a stream to the point where the
 223    * <code>mark()</code> method was called.  Any bytes that were read
 224    * after the mark point was set will be re-read during subsequent
 225    * reads.
 226    * <p>
 227    * This method always throws an IOException in this class, but subclasses
 228    * can override this method if they provide mark/reset functionality.
 229    *
 230    * @exception IOException Always thrown for this class
 231    */
 232   public void reset() throws IOException
 233   {
 234     throw new IOException("mark/reset not supported");
 235   }
 236
 237   /**
 238    * This method skips the specified number of bytes in the stream.  It
 239    * returns the actual number of bytes skipped, which may be less than the
 240    * requested amount.
 241    * <p>
 242    * This method reads and discards bytes into a byte array until the
 243    * specified number of bytes were skipped or until either the end of stream
 244    * is reached or a read attempt returns a short count.  Subclasses can
 245    * override this metho to provide a more efficient implementation where
 246    * one exists.
 247    *
 248    * @param n The requested number of bytes to skip
 249    *
 250    * @return The actual number of bytes skipped.
 251    *
 252    * @exception IOException If an error occurs
 253    */
 254   public long skip(long n) throws IOException
 255   {
 256     // Throw away n bytes by reading them into a temp byte[].
 257     // Limit the temp array to 2Kb so we don't grab too much memory.
 258     final int buflen = n > 2048 ? 2048 : (int) n;
 259     byte[] tmpbuf = new byte[buflen];
 260     final long origN = n;
 261
 262     while (n > 0L)
 263       {
 264         int numread = read(tmpbuf, 0, n > buflen ? buflen : (int) n);
 265         if (numread <= 0)
 266           break;
 267         n -= numread;
 268       }
 269
 270     return origN - n;
 271   }
 272 }