Netty源码分析-数据处理器ChannelInboundHandler和ChannelOutboundHandler

心已赠人 2022-04-03 15:26 744阅读 0赞

### 概述 ###

Channel接口针对Channel的读入和写出IO事件的处理，定义了两个拓展接口：ChannelInboundHandler用于定义对读入IO事件的处理，ChannelOutboundHandler用于定义写出IO事件的处理。

### ChannelInboundHandler ###

#### ChannelInboundHandler接口定义 ####

/** * {@link ChannelHandler} which adds callbacks for state changes. This allows the user * to hook in to state changes easily. */
    public interface ChannelInboundHandler extends ChannelHandler { 
    
        /** * The {@link Channel} of the {@link ChannelHandlerContext} was registered with its {@link EventLoop} */
        void channelRegistered(ChannelHandlerContext ctx) throws Exception;
    
        /** * The {@link Channel} of the {@link ChannelHandlerContext} was unregistered from its {@link EventLoop} */
        void channelUnregistered(ChannelHandlerContext ctx) throws Exception;
    
        /** * The {@link Channel} of the {@link ChannelHandlerContext} is now active */
        void channelActive(ChannelHandlerContext ctx) throws Exception;
    
        /** * The {@link Channel} of the {@link ChannelHandlerContext} was registered is now inactive and reached its * end of lifetime. */
        void channelInactive(ChannelHandlerContext ctx) throws Exception;
    
        /** * Invoked when the current {@link Channel} has read a message from the peer. */
        void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception;
    
        /** * Invoked when the last message read by the current read operation has been consumed by * {@link #channelRead(ChannelHandlerContext, Object)}. If {@link ChannelOption#AUTO_READ} is off, no further * attempt to read an inbound data from the current {@link Channel} will be made until * {@link ChannelHandlerContext#read()} is called. */
        void channelReadComplete(ChannelHandlerContext ctx) throws Exception;
    
        /** * Gets called if an user event was triggered. */
        void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception;
    
        /** * Gets called once the writable state of a {@link Channel} changed. You can check the state with * {@link Channel#isWritable()}. */
        void channelWritabilityChanged(ChannelHandlerContext ctx) throws Exception;
    
        /** * Gets called if a {@link Throwable} was thrown. */
        @Override
        @SuppressWarnings("deprecation")
        void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception;
    }

#### ChannelInboundHandlerAdapter ####

*  ChannelInboundHandler的默认实现类，方便使用，用户通过拓展该类，只重写与自身关注的IO事件的处理的方法。ChannelInboundHandlerAdapter的每个方法的默认实现都是通过ChannelHandlerContext将IO事件或接收到的数据，传给所在的ChannelPipeline的下一个ChannelInboundHandler：  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTAwMTM1NzM_size_16_color_FFFFFF_t_70]
 *  业务处理逻辑处理：用户可以通过拓展ChannelInboundHandlerAdapter，重写相应的方法来，生成新的子类的方式来定义业务需要的处理逻辑，Netty默认针对特定功能的处理，提供了一些ChannelInboundHandler的实现类，详见下面分析。
 *  对于从Channel读入的数据，在调用channelRead方法处理时，默认实现也是传给下一个ChannelInboundHandler处理，不会销毁该数据对象，释放掉该数据所占用的空间的：  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTAwMTM1NzM_size_16_color_FFFFFF_t_70 1]  
    如果数据只需在当前ChannelInboundHandler处理，而不需要继续往下传输，则可以调用ReferenceCountUtil.release(msg)手动释放掉，或者拓展SimpleChannelInboundHandler类。
 *  SimpleChannelInboundHandler  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTAwMTM1NzM_size_16_color_FFFFFF_t_70 2]  
    SimpleChannelInboundHandler为ChannelInboundHandlerAdapter的一个拓展实现，重写了channelRead方法，并提供了一个抽象方法channelRead0（在netty 5.0之后channelRead0方法名称变成了messageReceived）供用户实现自身的数据处理逻辑：  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTAwMTM1NzM_size_16_color_FFFFFF_t_70 3]  
    针对Channel读入的数据的处理，提供了两个功能：
    
    1.  特定类型数据处理：用户通过拓展实现SimpleChannelInboundHandler来定义业务处理的ChannelInboundHandler时，通过指定泛型参数I，限制该ChannelInboundHandler只处理Channel读入的类型为I的数据；
    2.  自动释放数据：如果Channel读入的数据的类型与泛型参数I匹配，则在该ChannelInboundHandler处理掉了，在finally中，根据调用构造函数创建ChannelInboundHandler时，是否需要自动释放数据（默认为true），来自动进行数据空间的释放。
    3.  数据的保留：如果用户在实现channelRead0方法自定义数据处理逻辑时，需要将该数据传给下一个ChannelInboundHandler，则需要调用ReferenceCountUtil.retain(msg)方法，原理是将msg的引用计数加1，因为ReferenceCountUtil.release(msg)是将msg的引用计数减1，同时当引用计数变成0时，释放该数据：

public class StringHandler extends SimpleChannelInboundHandler<String> { 
    
         @Override
         protected void channelRead0(ChannelHandlerContext ctx, String message)
                 throws Exception { 
             System.out.println(message);
             // 不释放数据，交给下一个ChannelInboundHandler继续处理
             ReferenceCountUtil.retain(message);
             ctx.fireChannelRead(message);
         }
     }

### ChannelOutboundHandler ###

#### ChannelOutboundHandler接口定义 ####

/** * {@link ChannelHandler} which will get notified for IO-outbound-operations. */
    public interface ChannelOutboundHandler extends ChannelHandler { 
        /** * Called once a bind operation is made. * * @param ctx the {@link ChannelHandlerContext} for which the bind operation is made * @param localAddress the {@link SocketAddress} to which it should bound * @param promise the {@link ChannelPromise} to notify once the operation completes * @throws Exception thrown if an error occurs */
        void bind(ChannelHandlerContext ctx, SocketAddress localAddress, ChannelPromise promise) throws Exception;
    
        /** * Called once a connect operation is made. * * @param ctx the {@link ChannelHandlerContext} for which the connect operation is made * @param remoteAddress the {@link SocketAddress} to which it should connect * @param localAddress the {@link SocketAddress} which is used as source on connect * @param promise the {@link ChannelPromise} to notify once the operation completes * @throws Exception thrown if an error occurs */
        void connect(
                ChannelHandlerContext ctx, SocketAddress remoteAddress,
                SocketAddress localAddress, ChannelPromise promise) throws Exception;
    
        /** * Called once a disconnect operation is made. * * @param ctx the {@link ChannelHandlerContext} for which the disconnect operation is made * @param promise the {@link ChannelPromise} to notify once the operation completes * @throws Exception thrown if an error occurs */
        void disconnect(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception;
    
        /** * Called once a close operation is made. * * @param ctx the {@link ChannelHandlerContext} for which the close operation is made * @param promise the {@link ChannelPromise} to notify once the operation completes * @throws Exception thrown if an error occurs */
        void close(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception;
    
        /** * Called once a deregister operation is made from the current registered {@link EventLoop}. * * @param ctx the {@link ChannelHandlerContext} for which the close operation is made * @param promise the {@link ChannelPromise} to notify once the operation completes * @throws Exception thrown if an error occurs */
        void deregister(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception;
    
        /** * Intercepts {@link ChannelHandlerContext#read()}. */
        void read(ChannelHandlerContext ctx) throws Exception;
    
        /** * Called once a write operation is made. The write operation will write the messages through the * {@link ChannelPipeline}. Those are then ready to be flushed to the actual {@link Channel} once * {@link Channel#flush()} is called * * @param ctx the {@link ChannelHandlerContext} for which the write operation is made * @param msg the message to write * @param promise the {@link ChannelPromise} to notify once the operation completes * @throws Exception thrown if an error occurs */
        void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception;
    
        /** * Called once a flush operation is made. The flush operation will try to flush out all previous written messages * that are pending. * * @param ctx the {@link ChannelHandlerContext} for which the flush operation is made * @throws Exception thrown if an error occurs */
        void flush(ChannelHandlerContext ctx) throws Exception;
    }

#### ChannelOutboundHandlerAdapter ####

![在这里插入图片描述][20181223143212692.png]  
与ChannelInboundHandlerAdapter的作用类似，方法默认实现也是通过ChannelHandlerContext将写出的数据，交给下一个ChannelOutboundHandler处理。

### ChannelDuplexHandler ###

![在这里插入图片描述][20181223143531544.png]  
同时具有ChannelInboundHandler和ChannelInboundHandler的功能，可以实现相应方法，对Channel的读入数据和写出数据都进行处理，默认实现也是交给下一个ChannelHandler处理。

### Netty提供的ChannelHandler实现 ###

Netty在handler子模块，针对不同的功能，包括流量控制，数据flush，ip过滤，日志，ssl，大数据流处理，超时心跳检测，拥塞控制，提供了相应的ChannelHandler实现类，如图：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTAwMTM1NzM_size_16_color_FFFFFF_t_70 4]

*  示例：心跳检测与长连接维持  
    [Netty源码分析-基于Netty的心跳检测机制实现长连接][Netty_-_Netty]

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[20181223143212692.png]: /images/20220403/b6ab63480ae94df9bc08ed08db6098f5.png
[20181223143531544.png]: /images/20220403/96b833a72ef046f1b19ad866104667c9.png
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[Netty_-_Netty]: https://blog.csdn.net/u010013573/article/details/85222823