libjava/java/io/SequenceInputStream.java

   1 /* SequenceInputStream.java -- Reads multiple input streams in sequence
   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 import java.util.Enumeration;
  42
  43 /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
  44  * "The Java Language Specification", ISBN 0-201-63451-1
  45  * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
  46  * Status:  Believed complete and correct.
  47  */
  48
  49 /**
  50   * This class merges a sequence of multiple <code>InputStream</code>'s in
  51   * order to form a single logical stream that can be read by applications
  52   * that expect only one stream.
  53   * <p>
  54   * The streams passed to the constructor method are read in order until
  55   * they return -1 to indicate they are at end of stream.  When a stream
  56   * reports end of stream, it is closed, then the next stream is read.
  57   * When the last stream is closed, the next attempt to read from this
  58   * stream will return a -1 to indicate it is at end of stream.
  59   * <p>
  60   * If this stream is closed prior to all subordinate streams being read
  61   * to completion, all subordinate streams are closed.
  62   *
  63   * @author Aaron M. Renn (arenn@urbanophile.com)
  64   * @author Warren Levy (warrenl@cygnus.com)
  65   */
  66 public class SequenceInputStream extends InputStream
  67 {
  68   /** The handle for the current input stream. */
  69   private InputStream in;
  70
  71   /** Secondary input stream; not used if constructed w/ enumeration. */
  72   private InputStream in2;
  73
  74   /** The enumeration handle; not used if constructed w/ 2 explicit input streams. */
  75   private Enumeration e;
  76
  77  /**
  78   * This method creates a new <code>SequenceInputStream</code> that obtains
  79   * its list of subordinate <code>InputStream</code>s from the specified
  80   * <code>Enumeration</code>
  81   *
  82   * @param e An <code>Enumeration</code> that will return a list of
  83   * <code>InputStream</code>s to read in sequence
  84   */
  85   public SequenceInputStream(Enumeration e)
  86   {
  87     this.e = e;
  88     in = (InputStream) e.nextElement();
  89     in2 = null;
  90   }
  91
  92  /**
  93   * This method creates a new <code>SequenceInputStream</code> that will read
  94   * the two specified subordinate <code>InputStream</code>s in sequence.
  95   *
  96   * @param s1 The first <code>InputStream</code> to read
  97   * @param s2 The second <code>InputStream</code> to read
  98   */
  99   public SequenceInputStream(InputStream s1, InputStream s2)
 100   {
 101     in = s1;
 102     in2 = s2;
 103   }
 104
 105  /**
 106   * This method returns the number of bytes than can be read from the
 107   * currently being read subordinate stream before that stream could
 108   * block.  Note that it is possible more bytes than this can actually
 109   * be read without the stream blocking.  If a 0 is returned, then the
 110   * stream could block on the very next read.
 111   *
 112   * @return The number of bytes that can be read before blocking could occur
 113   *
 114   * @exception IOException If an error occurs
 115   */
 116   public int available() throws IOException
 117   {
 118     if (in == null)
 119       return 0;
 120
 121     return in.available();
 122   }
 123
 124  /**
 125   * Closes this stream.  This will cause any remaining unclosed subordinate
 126   * <code>InputStream</code>'s to be closed as well.  Subsequent attempts to
 127   * read from this stream may cause an exception.
 128   *
 129   * @exception IOException If an error occurs
 130   */
 131   public void close() throws IOException
 132   {
 133     while (in != null)
 134       {
 135         in.close();
 136         in = getNextStream ();
 137       }
 138   }
 139
 140  /**
 141   * This method reads an unsigned byte from the input stream and returns it
 142   * as an int in the range of 0-255.  This method also will return -1 if
 143   * the end of the stream has been reached.  This will only happen when
 144   * all of the subordinate streams have been read.
 145   * <p>
 146   * This method will block until the byte can be read.
 147   *
 148   * @return The byte read, or -1 if end of stream
 149   *
 150   * @exception IOException If an error occurs
 151   */
 152   public int read() throws IOException
 153   {
 154     int ch = -1;
 155
 156     while (in != null && (ch = in.read()) < 0)
 157       {
 158         in.close();
 159         in = getNextStream();
 160       }
 161
 162     return ch;
 163   }
 164
 165  /**
 166   * This method reads bytes from a stream and stores them into a caller
 167   * supplied buffer.  It starts storing the data at index <code>offset</code>
 168   * into the buffer and attempts to read <code>len</code> bytes. This method
 169   * can return before reading the number of bytes requested. The actual number
 170   * of bytes read is returned as an int. A -1 is returend to indicate the
 171   * end of the stream. This will only happen when all of the subordinate
 172   * streams have been read.
 173   * <p>
 174   * This method will block until at least one byte can be read.
 175   *
 176   * @param b The array into which bytes read should be stored
 177   * @param off The offset into the array to start storing bytes
 178   * @param len The requested number of bytes to read
 179   *
 180   * @return The actual number of bytes read, or -1 if end of stream
 181   *
 182   * @exception IOException If an error occurs
 183   */
 184   public int read(byte[] b, int off, int len) throws IOException
 185   {
 186     int ch = -1;
 187
 188     // The validity of the parameters will be checked by in.read so
 189     // don't bother doing it here.
 190     while (in != null && (ch = in.read(b, off, len)) < 0)
 191       {
 192         in.close();
 193         in = getNextStream();
 194       }
 195
 196     return ch;
 197   }
 198
 199  /**
 200   * This private method is used to get the next <code>InputStream</code> to
 201   * read from. Returns null when no more streams are available.
 202   */
 203   private InputStream getNextStream()
 204   {
 205     InputStream nextIn = null;
 206
 207     if (e != null)
 208       {
 209         if (e.hasMoreElements())
 210           nextIn = (InputStream) e.nextElement();
 211       }
 212     else
 213       if (in2 != null)
 214         {
 215           nextIn = in2;
 216           in2 = null;
 217         }
 218
 219     return nextIn;
 220   }
 221 }