/*
* 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.
ChannelDuplexHandler;
import io.netty.channel.
ChannelHandlerContext;
import io.netty.channel.
ChannelPromise;
import io.netty.util.
ReferenceCounted;
import io.netty.util.internal.
TypeParameterMatcher;
import java.util.
List;
/**
* A Codec for on-the-fly encoding/decoding of message.
*
* This can be thought of as a combination of {@link MessageToMessageDecoder} and {@link MessageToMessageEncoder}.
*
* Here is an example of a {@link MessageToMessageCodec} which just decode from {@link Integer} to {@link Long}
* and encode from {@link Long} to {@link Integer}.
*
* <pre>
* public class NumberCodec extends
* {@link MessageToMessageCodec}<{@link Integer}, {@link Long}> {
* {@code @Override}
* public {@link Long} decode({@link ChannelHandlerContext} ctx, {@link Integer} msg, List<Object> out)
* throws {@link Exception} {
* out.add(msg.longValue());
* }
*
* {@code @Override}
* public {@link Integer} encode({@link ChannelHandlerContext} ctx, {@link Long} msg, List<Object> out)
* throws {@link Exception} {
* out.add(msg.intValue());
* }
* }
* </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 MessageToMessageCodec} will call
* {@link ReferenceCounted#release()} on encoded / decoded messages.
*/
public abstract class
MessageToMessageCodec<INBOUND_IN, OUTBOUND_IN> extends
ChannelDuplexHandler {
private final
MessageToMessageEncoder<
Object>
encoder = new
MessageToMessageEncoder<
Object>() {
@
Override
public boolean
acceptOutboundMessage(
Object msg) throws
Exception {
return
MessageToMessageCodec.this.
acceptOutboundMessage(
msg);
}
@
Override
@
SuppressWarnings("unchecked")
protected void
encode(
ChannelHandlerContext ctx,
Object msg,
List<
Object>
out) throws
Exception {
MessageToMessageCodec.this.
encode(
ctx, (OUTBOUND_IN)
msg,
out);
}
};
private final
MessageToMessageDecoder<
Object>
decoder = new
MessageToMessageDecoder<
Object>() {
@
Override
public boolean
acceptInboundMessage(
Object msg) throws
Exception {
return
MessageToMessageCodec.this.
acceptInboundMessage(
msg);
}
@
Override
@
SuppressWarnings("unchecked")
protected void
decode(
ChannelHandlerContext ctx,
Object msg,
List<
Object>
out) throws
Exception {
MessageToMessageCodec.this.
decode(
ctx, (INBOUND_IN)
msg,
out);
}
};
private final
TypeParameterMatcher inboundMsgMatcher;
private final
TypeParameterMatcher outboundMsgMatcher;
/**
* Create a new instance which will try to detect the types to decode and encode out of the type parameter
* of the class.
*/
protected
MessageToMessageCodec() {
inboundMsgMatcher =
TypeParameterMatcher.
find(this,
MessageToMessageCodec.class, "INBOUND_IN");
outboundMsgMatcher =
TypeParameterMatcher.
find(this,
MessageToMessageCodec.class, "OUTBOUND_IN");
}
/**
* Create a new instance.
*
* @param inboundMessageType The type of messages to decode
* @param outboundMessageType The type of messages to encode
*/
protected
MessageToMessageCodec(
Class<? extends INBOUND_IN>
inboundMessageType,
Class<? extends OUTBOUND_IN>
outboundMessageType) {
inboundMsgMatcher =
TypeParameterMatcher.
get(
inboundMessageType);
outboundMsgMatcher =
TypeParameterMatcher.
get(
outboundMessageType);
}
@
Override
public void
channelRead(
ChannelHandlerContext ctx,
Object msg) throws
Exception {
decoder.
channelRead(
ctx,
msg);
}
@
Override
public void
write(
ChannelHandlerContext ctx,
Object msg,
ChannelPromise promise) throws
Exception {
encoder.
write(
ctx,
msg,
promise);
}
/**
* Returns {@code true} if and only if the specified message can be decoded by this codec.
*
* @param msg the message
*/
public boolean
acceptInboundMessage(
Object msg) throws
Exception {
return
inboundMsgMatcher.
match(
msg);
}
/**
* Returns {@code true} if and only if the specified message can be encoded by this codec.
*
* @param msg the message
*/
public boolean
acceptOutboundMessage(
Object msg) throws
Exception {
return
outboundMsgMatcher.
match(
msg);
}
/**
* @see MessageToMessageEncoder#encode(ChannelHandlerContext, Object, List)
*/
protected abstract void
encode(
ChannelHandlerContext ctx, OUTBOUND_IN
msg,
List<
Object>
out)
throws
Exception;
/**
* @see MessageToMessageDecoder#decode(ChannelHandlerContext, Object, List)
*/
protected abstract void
decode(
ChannelHandlerContext ctx, INBOUND_IN
msg,
List<
Object>
out)
throws
Exception;
}