libjava/gnu/java/nio/ChannelReader.java

   1 /* ChannelReader.java --
   2  Copyright (C) 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 gnu.java.nio;
  40
  41 import java.io.IOException;
  42 import java.io.Reader;
  43 import java.nio.ByteBuffer;
  44 import java.nio.CharBuffer;
  45 import java.nio.channels.ReadableByteChannel;
  46 import java.nio.charset.CharsetDecoder;
  47 import java.nio.charset.CoderResult;
  48 import java.nio.charset.CodingErrorAction;
  49
  50 /**
  51  * A Reader implementation that works using a ReadableByteChannel and a
  52  * CharsetDecoder.
  53  *
  54  * <p>
  55  * This is a bridge between NIO <-> IO character decoding.
  56  * </p>
  57  *
  58  * @author Robert Schuster
  59  */
  60 public class ChannelReader extends Reader
  61 {
  62
  63   private static final int DEFAULT_BUFFER_CAP = 8192;
  64
  65   private ReadableByteChannel channel;
  66
  67   private CharsetDecoder decoder;
  68
  69   private ByteBuffer byteBuffer;
  70
  71   private CharBuffer charBuffer;
  72
  73   public ChannelReader(ReadableByteChannel channel, CharsetDecoder decoder,
  74                        int minBufferCap)
  75   {
  76     this.channel = channel;
  77     this.decoder = decoder;
  78
  79     // JDK reports errors, so we do the same.
  80     decoder.onMalformedInput(CodingErrorAction.REPORT);
  81     decoder.onUnmappableCharacter(CodingErrorAction.REPORT);
  82     decoder.reset();
  83
  84     int size = (minBufferCap == -1) ? DEFAULT_BUFFER_CAP : minBufferCap;
  85
  86     // Allocates the buffers and prepares them for reading, because that is the
  87     // first operation being done on them.
  88     byteBuffer = ByteBuffer.allocate(size);
  89     byteBuffer.flip();
  90     charBuffer = CharBuffer.allocate((int) (size * decoder.averageCharsPerByte()));
  91   }
  92
  93   public int read(char[] buf, int offset, int count) throws IOException
  94   {
  95     // I declared channel being null meaning that the reader is closed.
  96     if (!channel.isOpen())
  97       throw new IOException("Reader was already closed.");
  98
  99     // I declared decoder being null meaning that there is no more data to read
 100     // and convert.
 101     if (decoder == null)
 102       return -1;
 103
 104     // Stores the amount of character being read. It -1 so that if no conversion
 105     // occured the caller will see this as an 'end of file'.
 106     int sum = -1;
 107
 108     // Copies any characters which may be left from the last invocation into the
 109     // destination array.
 110     if (charBuffer.remaining() > 0)
 111       {
 112         sum = Math.min(count, charBuffer.remaining());
 113         charBuffer.get(buf, offset, sum);
 114
 115         // Updates the control variables according to the latest copy operation.
 116         offset += sum;
 117         count -= sum;
 118       }
 119
 120     // Copies the character which have not been put in the destination array to
 121     // the beginning. If data is actually copied count will be 0. If no data is
 122     // copied count is >0 and we can now convert some more characters.
 123     charBuffer.compact();
 124
 125     int converted = 0;
 126     boolean last = false;
 127
 128     while (count != 0)
 129       {
 130         // Tries to convert some bytes (Which will intentionally fail in the
 131         // first place because we have not read any bytes yet.)
 132         CoderResult result = decoder.decode(byteBuffer, charBuffer, last);
 133         if (result.isMalformed() || result.isUnmappable())
 134           {
 135             // JDK throws exception when bytes are malformed for sure.
 136             // FIXME: Unsure what happens when a character is simply
 137             // unmappable.
 138             result.throwException();
 139           }
 140
 141         // Marks that we should end this loop regardless whether the caller
 142         // wants more chars or not, when this was the last conversion.
 143         if (last)
 144           {
 145             decoder = null;
 146           }
 147         else if (result.isUnderflow())
 148           {
 149             // We need more bytes to do the conversion.
 150
 151             // Copies the not yet converted bytes to the beginning making it
 152             // being able to receive more bytes.
 153             byteBuffer.compact();
 154
 155             // Reads in another bunch of bytes for being converted.
 156             if (channel.read(byteBuffer) == -1)
 157               {
 158                 // If there is no more data available in the channel we mark
 159                 // that state for the final character conversion run which is
 160                 // done in the next loop iteration.
 161                 last = true;
 162               }
 163
 164             // Prepares the byteBuffer for the next character conversion run.
 165             byteBuffer.flip();
 166           }
 167
 168         // Prepares the charBuffer for being drained.
 169         charBuffer.flip();
 170
 171         converted = Math.min(count, charBuffer.remaining());
 172         charBuffer.get(buf, offset, converted);
 173
 174         // Copies characters which have not yet being copied into the char-Array
 175         // to the beginning making it possible to read them later (If data is
 176         // really copied here, then the caller has received enough characters so
 177         // far.).
 178         charBuffer.compact();
 179
 180         // Updates the control variables according to the latest copy operation.
 181         offset += converted;
 182         count -= converted;
 183
 184         // Updates the amount of transferred characters.
 185         sum += converted;
 186
 187         if (decoder == null)
 188           {
 189             break;
 190           }
 191
 192         // Now that more characters have been transfered we let the loop decide
 193         // what to do next.
 194       }
 195
 196     // Makes the charBuffer ready for reading on the next invocation.
 197     charBuffer.flip();
 198
 199     return sum;
 200   }
 201
 202   public void close() throws IOException
 203   {
 204     channel.close();
 205
 206     // Makes sure all intermediate data is released by the decoder.
 207     if (decoder != null)
 208       decoder.reset();
 209   }
 210
 211 }