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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.oneone;
    17
    18  import static org.jboss.netty.channel.Channels.*;
    19
    20  import org.jboss.netty.buffer.ChannelBuffers;
    21  import org.jboss.netty.channel.Channel;
    22  import org.jboss.netty.channel.ChannelDownstreamHandler;
    23  import org.jboss.netty.channel.ChannelEvent;
    24  import org.jboss.netty.channel.ChannelHandlerContext;
    25  import org.jboss.netty.channel.ChannelPipeline;
    26  import org.jboss.netty.channel.MessageEvent;
    27  import org.jboss.netty.handler.codec.frame.DelimiterBasedFrameDecoder;
    28  import org.jboss.netty.handler.codec.frame.Delimiters;
    29
    30  /**
    31   * Transforms a write request into another write request.  A typical setup for
    32   * TCP/IP would be:
    33   * <pre>
    34   * {@link ChannelPipeline} pipeline = ...;
    35   *
    36   * // Decoders
    37   * pipeline.addLast("frameDecoder", new {@link DelimiterBasedFrameDecoder}(80, {@link Delimiters#nulDelimiter()}));
    38   * pipeline.addLast("customDecoder", new {@link OneToOneDecoder}() { ... });
    39   *
    40   * // Encoder
    41   * pipeline.addLast("customEncoder", new {@link OneToOneEncoder}() { ... });
    42   * </pre>
    43   *
    44   * @apiviz.landmark
    45   */
    46  public abstract class OneToOneEncoder implements ChannelDownstreamHandler {
    47
    48      protected OneToOneEncoder() {
    49          super();
    50      }
    51
    52      public void handleDownstream(
    53              ChannelHandlerContext ctx, ChannelEvent evt) throws Exception {
    54          if (!(evt instanceof MessageEvent)) {
    55              ctx.sendDownstream(evt);
    56              return;
    57          }
    58
    59          MessageEvent e = (MessageEvent) evt;
    60          Object originalMessage = e.getMessage();
    61          Object encodedMessage = encode(ctx, e.getChannel(), originalMessage);
    62          if (originalMessage == encodedMessage) {
    63              ctx.sendDownstream(evt);
    64          } else if (encodedMessage != null) {
    65              write(ctx, e.getFuture(), encodedMessage, e.getRemoteAddress());
    66          }
    67      }
    68
    69      /**
    70       * Transforms the specified message into another message and return the
    71       * transformed message.  Note that you can not return {@code null}, unlike
    72       * you can in {@link OneToOneDecoder#decode(ChannelHandlerContext, Channel, Object)};
    73       * you must return something, at least {@link ChannelBuffers#EMPTY_BUFFER}.
    74       */
    75      protected abstract Object encode(
    76              ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception;
    77  }