/*
* 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.buffer.
ByteBuf;
import io.netty.buffer.
Unpooled;
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.internal.
TypeParameterMatcher;
/**
* {@link ChannelOutboundHandlerAdapter} which encodes message in a stream-like fashion from one message to an
* {@link ByteBuf}.
*
*
* Example implementation which encodes {@link Integer}s to a {@link ByteBuf}.
*
* <pre>
* public class IntegerEncoder extends {@link MessageToByteEncoder}<{@link Integer}> {
* {@code @Override}
* public void encode({@link ChannelHandlerContext} ctx, {@link Integer} msg, {@link ByteBuf} out)
* throws {@link Exception} {
* out.writeInt(msg);
* }
* }
* </pre>
*/
public abstract class
MessageToByteEncoder<I> extends
ChannelOutboundHandlerAdapter {
private final
TypeParameterMatcher matcher;
private final boolean
preferDirect;
/**
* see {@link #MessageToByteEncoder(boolean)} with {@code true} as boolean parameter.
*/
protected
MessageToByteEncoder() {
this(true);
}
/**
* see {@link #MessageToByteEncoder(Class, boolean)} with {@code true} as boolean value.
*/
protected
MessageToByteEncoder(
Class<? extends I>
outboundMessageType) {
this(
outboundMessageType, true);
}
/**
* Create a new instance which will try to detect the types to match out of the type parameter of the class.
*
* @param preferDirect {@code true} if a direct {@link ByteBuf} should be tried to be used as target for
* the encoded messages. If {@code false} is used it will allocate a heap
* {@link ByteBuf}, which is backed by an byte array.
*/
protected
MessageToByteEncoder(boolean
preferDirect) {
matcher =
TypeParameterMatcher.
find(this,
MessageToByteEncoder.class, "I");
this.
preferDirect =
preferDirect;
}
/**
* Create a new instance
*
* @param outboundMessageType The type of messages to match
* @param preferDirect {@code true} if a direct {@link ByteBuf} should be tried to be used as target for
* the encoded messages. If {@code false} is used it will allocate a heap
* {@link ByteBuf}, which is backed by an byte array.
*/
protected
MessageToByteEncoder(
Class<? extends I>
outboundMessageType, boolean
preferDirect) {
matcher =
TypeParameterMatcher.
get(
outboundMessageType);
this.
preferDirect =
preferDirect;
}
/**
* 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 {
ByteBuf buf = null;
try {
if (
acceptOutboundMessage(
msg)) {
@
SuppressWarnings("unchecked")
I
cast = (I)
msg;
buf =
allocateBuffer(
ctx,
cast,
preferDirect);
try {
encode(
ctx,
cast,
buf);
} finally {
ReferenceCountUtil.
release(
cast);
}
if (
buf.
isReadable()) {
ctx.
write(
buf,
promise);
} else {
buf.
release();
ctx.
write(
Unpooled.
EMPTY_BUFFER,
promise);
}
buf = null;
} else {
ctx.
write(
msg,
promise);
}
} catch (
EncoderException e) {
throw
e;
} catch (
Throwable e) {
throw new
EncoderException(
e);
} finally {
if (
buf != null) {
buf.
release();
}
}
}
/**
* Allocate a {@link ByteBuf} which will be used as argument of {@link #encode(ChannelHandlerContext, I, ByteBuf)}.
* Sub-classes may override this method to return {@link ByteBuf} with a perfect matching {@code initialCapacity}.
*/
protected
ByteBuf allocateBuffer(
ChannelHandlerContext ctx, @
SuppressWarnings("unused") I
msg,
boolean
preferDirect) throws
Exception {
if (
preferDirect) {
return
ctx.
alloc().
ioBuffer();
} else {
return
ctx.
alloc().
heapBuffer();
}
}
/**
* Encode a message into a {@link ByteBuf}. This method will be called for each written message that can be handled
* by this encoder.
*
* @param ctx the {@link ChannelHandlerContext} which this {@link MessageToByteEncoder} belongs to
* @param msg the message to encode
* @param out the {@link ByteBuf} into which the encoded message will be written
* @throws Exception is thrown if an error occurs
*/
protected abstract void
encode(
ChannelHandlerContext ctx, I
msg,
ByteBuf out) throws
Exception;
protected boolean
isPreferDirect() {
return
preferDirect;
}
}