/*
* 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}.
*
* <pre>
* 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());
* }
* }
* </pre>
*
* 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<I> 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<? extends I>
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 encoder.
*
* @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<
Object>
out) throws
Exception;
}