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/*
* Copyright 2012 The Netty Project
*
* The Netty Project licenses this file to you under the Apache License,
* version 2.0 (the "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*/
package io.netty.handler.codec;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandler;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelPipeline;
import io.netty.util.ReferenceCountUtil;
import io.netty.util.ReferenceCounted;
import io.netty.util.internal.TypeParameterMatcher;
import java.util.List;
/**
* {@link ChannelInboundHandlerAdapter} which decodes from one message to an other message.
*
*
* For example here is an implementation which decodes a {@link String} to an {@link Integer} which represent
* the length of the {@link String}.
*
*
* public class StringToIntegerDecoder extends
* {@link MessageToMessageDecoder}<{@link String}> {
*
* {@code @Override}
* public void decode({@link ChannelHandlerContext} ctx, {@link String} message,
* List<Object> out) throws {@link Exception} {
* out.add(message.length());
* }
* }
*
*
* Be aware that you need to call {@link ReferenceCounted#retain()} on messages that are just passed through if they
* are of type {@link ReferenceCounted}. This is needed as the {@link MessageToMessageDecoder} will call
* {@link ReferenceCounted#release()} on decoded messages.
*
*/
public abstract class MessageToMessageDecoder extends ChannelInboundHandlerAdapter {
private final TypeParameterMatcher matcher;
/**
* Create a new instance which will try to detect the types to match out of the type parameter of the class.
*/
protected MessageToMessageDecoder() {
matcher = TypeParameterMatcher.find(this, MessageToMessageDecoder.class, "I");
}
/**
* Create a new instance
*
* @param inboundMessageType The type of messages to match and so decode
*/
protected MessageToMessageDecoder(Class inboundMessageType) {
matcher = TypeParameterMatcher.get(inboundMessageType);
}
/**
* Returns {@code true} if the given message should be handled. If {@code false} it will be passed to the next
* {@link ChannelInboundHandler} in the {@link ChannelPipeline}.
*/
public boolean acceptInboundMessage(Object msg) throws Exception {
return matcher.match(msg);
}
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
CodecOutputList out = CodecOutputList.newInstance();
try {
if (acceptInboundMessage(msg)) {
@SuppressWarnings("unchecked")
I cast = (I) msg;
try {
decode(ctx, cast, out);
} finally {
ReferenceCountUtil.release(cast);
}
} else {
out.add(msg);
}
} catch (DecoderException e) {
throw e;
} catch (Exception e) {
throw new DecoderException(e);
} finally {
int size = out.size();
for (int i = 0; i < size; i ++) {
ctx.fireChannelRead(out.getUnsafe(i));
}
out.recycle();
}
}
/**
* Decode from one message to an other. This method will be called for each written message that can be handled
* by this decoder.
*
* @param ctx the {@link ChannelHandlerContext} which this {@link MessageToMessageDecoder} belongs to
* @param msg the message to decode to an other one
* @param out the {@link List} to which decoded messages should be added
* @throws Exception is thrown if an error occurs
*/
protected abstract void decode(ChannelHandlerContext ctx, I msg, List