144 lines
5.5 KiB
Java
144 lines
5.5 KiB
Java
/*
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* Copyright 2012 The Netty Project
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*
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* The Netty Project licenses this file to you under the Apache License,
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* version 2.0 (the "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at:
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*
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* https://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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package io.netty.handler.codec;
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import io.netty.channel.ChannelHandler;
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import io.netty.channel.ChannelHandlerAdapter;
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import io.netty.channel.ChannelHandlerContext;
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import io.netty.channel.ChannelPipeline;
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import io.netty.util.ReferenceCountUtil;
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import io.netty.util.ReferenceCounted;
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import io.netty.util.concurrent.Future;
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import io.netty.util.concurrent.Promise;
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import io.netty.util.concurrent.PromiseCombiner;
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import io.netty.util.internal.StringUtil;
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import io.netty.util.internal.TypeParameterMatcher;
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import java.util.List;
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/**
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* {@link ChannelHandler} which encodes from one message to an other message
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*
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* For example here is an implementation which decodes an {@link Integer} to an {@link String}.
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*
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* <pre>
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* public class IntegerToStringEncoder extends
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* {@link MessageToMessageEncoder}<{@link Integer}> {
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*
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* {@code @Override}
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* public void encode({@link ChannelHandlerContext} ctx, {@link Integer} message, List<Object> out)
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* throws {@link Exception} {
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* out.add(message.toString());
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* }
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* }
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* </pre>
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*
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* Be aware that you need to call {@link ReferenceCounted#retain()} on messages that are just passed through if they
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* are of type {@link ReferenceCounted}. This is needed as the {@link MessageToMessageEncoder} will call
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* {@link ReferenceCounted#release()} on encoded messages.
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*/
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public abstract class MessageToMessageEncoder<I> extends ChannelHandlerAdapter {
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private final TypeParameterMatcher matcher;
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/**
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* Create a new instance which will try to detect the types to match out of the type parameter of the class.
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*/
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protected MessageToMessageEncoder() {
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matcher = TypeParameterMatcher.find(this, MessageToMessageEncoder.class, "I");
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}
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/**
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* Create a new instance
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*
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* @param outboundMessageType The type of messages to match and so encode
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*/
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protected MessageToMessageEncoder(Class<? extends I> outboundMessageType) {
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matcher = TypeParameterMatcher.get(outboundMessageType);
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}
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/**
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* Returns {@code true} if the given message should be handled. If {@code false} it will be passed to the next
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* {@link ChannelHandler} in the {@link ChannelPipeline}.
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*/
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public boolean acceptOutboundMessage(Object msg) throws Exception {
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return matcher.match(msg);
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}
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@Override
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public Future<Void> write(ChannelHandlerContext ctx, Object msg) {
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CodecOutputList out = null;
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try {
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if (acceptOutboundMessage(msg)) {
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out = CodecOutputList.newInstance();
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@SuppressWarnings("unchecked")
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I cast = (I) msg;
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Promise<Void> promise = ctx.newPromise();
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try {
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try {
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encode(ctx, cast, out);
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} finally {
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ReferenceCountUtil.release(cast);
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}
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if (out.isEmpty()) {
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throw new EncoderException(
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StringUtil.simpleClassName(this) + " must produce at least one message.");
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}
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} finally {
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final int sizeMinusOne = out.size() - 1;
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if (sizeMinusOne == 0) {
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ctx.write(out.getUnsafe(0)).cascadeTo(promise);
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} else {
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writePromiseCombiner(ctx, out, promise);
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}
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}
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return promise.asFuture();
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} else {
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return ctx.write(msg);
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}
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} catch (EncoderException e) {
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return ctx.newFailedFuture(e);
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} catch (Throwable t) {
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return ctx.newFailedFuture(new EncoderException(t));
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} finally {
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if (out != null) {
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out.recycle();
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}
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}
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}
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private static void writePromiseCombiner(ChannelHandlerContext ctx, CodecOutputList out, Promise<Void> promise) {
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final PromiseCombiner combiner = new PromiseCombiner(ctx.executor());
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for (int i = 0; i < out.size(); i++) {
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combiner.add(ctx.write(out.getUnsafe(i)));
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}
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combiner.finish(promise);
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}
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/**
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* Encode from one message to an other. This method will be called for each written message that can be handled
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* by this encoder.
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*
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* @param ctx the {@link ChannelHandlerContext} which this {@link MessageToMessageEncoder} belongs to
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* @param msg the message to encode to an other one
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* @param out the {@link List} into which the encoded msg should be added
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* needs to do some kind of aggregation
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* @throws Exception is thrown if an error occurs
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*/
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protected abstract void encode(ChannelHandlerContext ctx, I msg, List<Object> out) throws Exception;
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}
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