/*
* 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.
ChannelOutboundHandler;
import io.netty.channel.
ChannelOutboundHandlerAdapter;
import io.netty.channel.
ChannelPipeline;
import io.netty.channel.
ChannelPromise;
import io.netty.util.
ReferenceCountUtil;
import io.netty.util.
ReferenceCounted;
import io.netty.util.internal.
StringUtil;
import io.netty.util.internal.
TypeParameterMatcher;
import java.util.
List;
/**
* {@link ChannelOutboundHandlerAdapter} which encodes from one message to an other message
*
* For example here is an implementation which decodes an {@link Integer} to an {@link String}.
*
* <pre>
* public class IntegerToStringEncoder extends
* {@link MessageToMessageEncoder}<{@link Integer}> {
*
* {@code @Override}
* public void encode({@link ChannelHandlerContext} ctx, {@link Integer} message, List<Object> out)
* throws {@link Exception} {
* out.add(message.toString());
* }
* }
* </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 MessageToMessageEncoder} will call
* {@link ReferenceCounted#release()} on encoded messages.
*/
public abstract class
MessageToMessageEncoder<I> extends
ChannelOutboundHandlerAdapter {
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
MessageToMessageEncoder() {
matcher =
TypeParameterMatcher.
find(this,
MessageToMessageEncoder.class, "I");
}
/**
* Create a new instance
*
* @param outboundMessageType The type of messages to match and so encode
*/
protected
MessageToMessageEncoder(
Class<? extends I>
outboundMessageType) {
matcher =
TypeParameterMatcher.
get(
outboundMessageType);
}
/**
* Returns {@code true} if the given message should be handled. If {@code false} it will be passed to the next
* {@link ChannelOutboundHandler} in the {@link ChannelPipeline}.
*/
public boolean
acceptOutboundMessage(
Object msg) throws
Exception {
return
matcher.
match(
msg);
}
@
Override
public void
write(
ChannelHandlerContext ctx,
Object msg,
ChannelPromise promise) throws
Exception {
CodecOutputList out = null;
try {
if (
acceptOutboundMessage(
msg)) {
out =
CodecOutputList.
newInstance();
@
SuppressWarnings("unchecked")
I
cast = (I)
msg;
try {
encode(
ctx,
cast,
out);
} finally {
ReferenceCountUtil.
release(
cast);
}
if (
out.
isEmpty()) {
out.
recycle();
out = null;
throw new
EncoderException(
StringUtil.
simpleClassName(this) + " must produce at least one message.");
}
} else {
ctx.
write(
msg,
promise);
}
} catch (
EncoderException e) {
throw
e;
} catch (
Throwable t) {
throw new
EncoderException(
t);
} finally {
if (
out != null) {
final int
sizeMinusOne =
out.
size() - 1;
if (
sizeMinusOne == 0) {
ctx.
write(
out.
get(0),
promise);
} else if (
sizeMinusOne > 0) {
// Check if we can use a voidPromise for our extra writes to reduce GC-Pressure
// See https://github.com/netty/netty/issues/2525
ChannelPromise voidPromise =
ctx.
voidPromise();
boolean
isVoidPromise =
promise ==
voidPromise;
for (int
i = 0;
i <
sizeMinusOne;
i ++) {
ChannelPromise p;
if (
isVoidPromise) {
p =
voidPromise;
} else {
p =
ctx.
newPromise();
}
ctx.
write(
out.
getUnsafe(
i),
p);
}
ctx.
write(
out.
getUnsafe(
sizeMinusOne),
promise);
}
out.
recycle();
}
}
}
/**
* Encode 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 MessageToMessageEncoder} belongs to
* @param msg the message to encode to an other one
* @param out the {@link List} into which the encoded msg should be added
* needs to do some kind of aggregation
* @throws Exception is thrown if an error occurs
*/
protected abstract void
encode(
ChannelHandlerContext ctx, I
msg,
List<
Object>
out) throws
Exception;
}