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    1   /*
    2    * Copyright 2012 The Netty Project
    3    *
    4    * The Netty Project licenses this file to you under the Apache License,
    5    * version 2.0 (the "License"); you may not use this file except in compliance
    6    * with the 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.ChannelHandler.Sharable;
    23  import org.jboss.netty.channel.ChannelHandlerContext;
    24  import org.jboss.netty.channel.ChannelPipeline;
    25  import org.jboss.netty.channel.MessageEvent;
    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   * @apiviz.landmark
    57   */
    58  @Sharable
    59  public class StringDecoder extends OneToOneDecoder {
    60
    61      // TODO Use CharsetDecoder instead.
    62      private final Charset charset;
    63
    64      /**
    65       * Creates a new instance with the current system character set.
    66       */
    67      public StringDecoder() {
    68          this(Charset.defaultCharset());
    69      }
    70
    71      /**
    72       * Creates a new instance with the specified character set.
    73       */
    74      public StringDecoder(Charset charset) {
    75          if (charset == null) {
    76              throw new NullPointerException("charset");
    77          }
    78          this.charset = charset;
    79      }
    80
    81      /**
    82       * @deprecated Use {@link #StringDecoder(Charset)} instead.
    83       */
    84      @Deprecated
    85      public StringDecoder(String charsetName) {
    86          this(Charset.forName(charsetName));
    87      }
    88
    89      @Override
    90      protected Object decode(
    91              ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception {
    92          if (!(msg instanceof ChannelBuffer)) {
    93              return msg;
    94          }
    95          return ((ChannelBuffer) msg).toString(charset);
    96      }
    97  }