Source for java.io.SequenceInputStream

   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., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 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: }