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    1   /*
    2    * Copyright 2009 Red Hat, Inc.
    3    *
    4    * Red Hat licenses this file to you under the Apache License, version 2.0
    5    * (the "License"); you may not use this file except in compliance with the
    6    * License.  You may obtain a copy of the License at:
    7    *
    8    *    http://www.apache.org/licenses/LICENSE-2.0
    9    *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
    12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
    13   * License for the specific language governing permissions and limitations
    14   * under the License.
    15   */
    16  package org.jboss.netty.handler.codec.string;
    17
    18  import java.nio.charset.Charset;
    19
    20  import org.jboss.netty.buffer.ChannelBuffer;
    21  import org.jboss.netty.channel.Channel;
    22  import org.jboss.netty.channel.ChannelHandlerContext;
    23  import org.jboss.netty.channel.ChannelPipeline;
    24  import org.jboss.netty.channel.MessageEvent;
    25  import org.jboss.netty.channel.ChannelHandler.Sharable;
    26  import org.jboss.netty.handler.codec.frame.DelimiterBasedFrameDecoder;
    27  import org.jboss.netty.handler.codec.frame.Delimiters;
    28  import org.jboss.netty.handler.codec.frame.FrameDecoder;
    29  import org.jboss.netty.handler.codec.oneone.OneToOneDecoder;
    30
    31  /**
    32   * Decodes a received {@link ChannelBuffer} into a {@link String}.  Please
    33   * note that this decoder must be used with a proper {@link FrameDecoder}
    34   * such as {@link DelimiterBasedFrameDecoder} if you are using a stream-based
    35   * transport such as TCP/IP.  A typical setup for a text-based line protocol
    36   * in a TCP/IP socket would be:
    37   * <pre>
    38   * {@link ChannelPipeline} pipeline = ...;
    39   *
    40   * // Decoders
    41   * pipeline.addLast("frameDecoder", new {@link DelimiterBasedFrameDecoder}(80, {@link Delimiters#lineDelimiter()}));
    42   * pipeline.addLast("stringDecoder", new {@link StringDecoder}(CharsetUtil.UTF_8));
    43   *
    44   * // Encoder
    45   * pipeline.addLast("stringEncoder", new {@link StringEncoder}(CharsetUtil.UTF_8));
    46   * </pre>
    47   * and then you can use a {@link String} instead of a {@link ChannelBuffer}
    48   * as a message:
    49   * <pre>
    50   * void messageReceived({@link ChannelHandlerContext} ctx, {@link MessageEvent} e) {
    51   *     String msg = (String) e.getMessage();
    52   *     ch.write("Did you say '" + msg + "'?\n");
    53   * }
    54   * </pre>
    55   *
    56   * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
    57   * @author <a href="http://gleamynode.net/">Trustin Lee</a>
    58   *
    59   * @version $Rev:231 $, $Date:2008-06-12 16:44:50 +0900 (목, 12 6월 2008) $
    60   *
    61   * @apiviz.landmark
    62   */
    63  @Sharable
    64  public class StringDecoder extends OneToOneDecoder {
    65
    66      // TODO Use CharsetDecoder instead.
    67      private final Charset charset;
    68
    69      /**
    70       * Creates a new instance with the current system character set.
    71       */
    72      public StringDecoder() {
    73          this(Charset.defaultCharset());
    74      }
    75
    76      /**
    77       * Creates a new instance with the specified character set.
    78       */
    79      public StringDecoder(Charset charset) {
    80          if (charset == null) {
    81              throw new NullPointerException("charset");
    82          }
    83          this.charset = charset;
    84      }
    85
    86      /**
    87       * @deprecated Use {@link #StringDecoder(Charset)} instead.
    88       */
    89      @Deprecated
    90      public StringDecoder(String charsetName) {
    91          this(Charset.forName(charsetName));
    92      }
    93
    94      @Override
    95      protected Object decode(
    96              ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception {
    97          if (!(msg instanceof ChannelBuffer)) {
    98              return msg;
    99          }
    100         return ((ChannelBuffer) msg).toString(charset);
    101     }
    102 }