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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.oneone;
    17
    18  import static org.jboss.netty.channel.Channels.*;
    19
    20  import org.jboss.netty.channel.Channel;
    21  import org.jboss.netty.channel.ChannelEvent;
    22  import org.jboss.netty.channel.ChannelHandlerContext;
    23  import org.jboss.netty.channel.ChannelPipeline;
    24  import org.jboss.netty.channel.ChannelUpstreamHandler;
    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
    30  /**
    31   * Transforms a received message into another message.  Please note that this
    32   * decoder must be used with a proper {@link FrameDecoder} such as
    33   * {@link DelimiterBasedFrameDecoder} or you must implement proper framing
    34   * mechanism by yourself if you are using a stream-based transport such as
    35   * TCP/IP.  A typical setup for TCP/IP would be:
    36   * <pre>
    37   * {@link ChannelPipeline} pipeline = ...;
    38   *
    39   * // Decoders
    40   * pipeline.addLast("frameDecoder", new {@link DelimiterBasedFrameDecoder}(80, {@link Delimiters#nulDelimiter()}));
    41   * pipeline.addLast("customDecoder", new {@link OneToOneDecoder}() { ... });
    42   *
    43   * // Encoder
    44   * pipeline.addLast("customEncoder", new {@link OneToOneEncoder}() { ... });
    45   * </pre>
    46   *
    47   * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
    48   * @author <a href="http://gleamynode.net/">Trustin Lee</a>
    49   *
    50   * @version $Rev:231 $, $Date:2008-06-12 16:44:50 +0900 (목, 12 6월 2008) $
    51   *
    52   * @apiviz.landmark
    53   */
    54  public abstract class OneToOneDecoder implements ChannelUpstreamHandler {
    55
    56      /**
    57       * Creates a new instance with the current system character set.
    58       */
    59      protected OneToOneDecoder() {
    60          super();
    61      }
    62
    63      public void handleUpstream(
    64              ChannelHandlerContext ctx, ChannelEvent evt) throws Exception {
    65          if (!(evt instanceof MessageEvent)) {
    66              ctx.sendUpstream(evt);
    67              return;
    68          }
    69
    70          MessageEvent e = (MessageEvent) evt;
    71          Object originalMessage = e.getMessage();
    72          Object decodedMessage = decode(ctx, e.getChannel(), originalMessage);
    73          if (originalMessage == decodedMessage) {
    74              ctx.sendUpstream(evt);
    75          } else if (decodedMessage != null) {
    76              fireMessageReceived(ctx, decodedMessage, e.getRemoteAddress());
    77          }
    78      }
    79
    80      /**
    81       * Transforms the specified received message into another message and return
    82       * the transformed message.  Return {@code null} if the received message
    83       * is supposed to be discarded.
    84       */
    85      protected abstract Object decode(
    86              ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception;
    87  }