Netty 学习笔记（3） ------ ChannelPipeline 和 ChannelHandler

ChannelPipeline通过责任链设计模式组织逻辑代码（ChannelHandler）,ChannelHander就如同Servlet的Filter一样一层层处理Channel的读写数据。

ChannelPipeline和ChannelHander的构成

1. Channel Netty框架中，一个连接对应一个Channel
2. ChannelPipeline 一个Channel绑定一条ChannelPipeline，ChannelPipeline以双向链表的结构组织所属Channel的所有逻辑处理器ChannelHandler
3. ChannelHandler 逻辑处理器，ChannelHandler分为ChannelInboundHandler入站处理器（处理读请求）和ChannelOutboundHandler出站处理器（处理写请求）。一个ChannelHander可以添加到多条ChannelPipeline上。
4. ChannelHanderContext ChannelHandler添加到一条ChannelPipeline后，该Channelpipeline将创建一个ChannelHandlerContext与ChannelHandler绑定。ChannelHandlerContext能够拿到Channel相关的上下文信息。

ChannelInboundHandler 和 ChannelOutboundHandler

1. ChannelInboundHandler 入站处理器，主要处理读请求的逻辑，它将按照它被添加的顺序处理数据。
2. ChannelOutboundHandler 出站处理器，主要处理写请求的逻辑，它将按照被添加的反顺序处理数据。
3. ChannelInboundHandlerAdapter和ChannelOutboundHandlerAdapter 实现了两大接口的所有功能，默认将事件提交给下一个处理器。

代码例子

入站处理器inboundHandler打印接受数据然后提交给下一个处理器，而出站处理器outboundHander打印写出数据然后提交给下一个处理器，writerHander在有客户端连接成功时写出helloClinet。

    public class HanderServerDemo {

	    public static void main(String[] args) {
	        HanderServerDemo server = new HanderServerDemo();
	        server.init();
	    }
	
	    public void init(){
	        NioEventLoopGroup bossGroup = new NioEventLoopGroup();
	        NioEventLoopGroup workerGroup = new NioEventLoopGroup();
	
	        ServerBootstrap serverBootstrap = new ServerBootstrap();
	        serverBootstrap.group(bossGroup, workerGroup)
	                .localAddress(8000)
	                .channel(NioServerSocketChannel.class)
	                .childHandler(new ChannelInitializer<SocketChannel>() {
	                    @Override
	                    protected void initChannel(SocketChannel socketChannel) throws Exception {
	                        // inBound，处理读数据的逻辑链
	                        socketChannel.pipeline().addLast(new InBoundHandlerA());
	                        socketChannel.pipeline().addLast(new InBoundHandlerB());
	                        socketChannel.pipeline().addLast(new InBoundHandlerC());
	
	                        //channel连接成功，返回hello client
	                        socketChannel.pipeline().addLast(new WriteHandler());
	
	                        // outBound，处理写数据的逻辑链
	                        socketChannel.pipeline().addLast(new OutBoundHandlerA());
	                        socketChannel.pipeline().addLast(new OutBoundHandlerB());
	                        socketChannel.pipeline().addLast(new OutBoundHandlerC());
	                    }
	                });
	        serverBootstrap.bind().addListener((future)->{
	            if(future.isSuccess()){
	                System.out.println("端口绑定成功");
	            }else{
	                System.out.println("端口绑定失败:"+future.cause());
	            }
	        });
	    }
	
	    public class InBoundHandlerA extends ChannelInboundHandlerAdapter {
	        @Override
	        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
	            System.out.println("InBoundHandlerA: " + msg);
	            super.channelRead(ctx, msg);
	        }
	    }
	
	    public class InBoundHandlerB extends ChannelInboundHandlerAdapter {
	        @Override
	        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
	            System.out.println("InBoundHandlerB: " + msg);
	            super.channelRead(ctx, msg);
	        }
	    }
	
	    public class InBoundHandlerC extends ChannelInboundHandlerAdapter {
	        @Override
	        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
	            System.out.println("InBoundHandlerC: " + msg);
	            super.channelRead(ctx, msg);
	        }
	    }
	
	    public class WriteHandler extends ChannelInboundHandlerAdapter {
	        @Override
	        public void channelActive(ChannelHandlerContext ctx) throws Exception {
	            ctx.channel().writeAndFlush(Unpooled.copiedBuffer("hello client".getBytes()));
	        }
	    }
	
	    public class OutBoundHandlerA extends ChannelOutboundHandlerAdapter {
	        @Override
	        public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
	            System.out.println("OutBoundHandlerA: " + msg);
	            super.write(ctx, msg, promise);
	        }
	    }
	
	    public class OutBoundHandlerB extends ChannelOutboundHandlerAdapter {
	        @Override
	        public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
	            System.out.println("OutBoundHandlerB: " + msg);
	            super.write(ctx, msg, promise);
	        }
	    }
	
	    public class OutBoundHandlerC extends ChannelOutboundHandlerAdapter {
	        public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
	            System.out.println("OutBoundHandlerC: " + msg);
	            super.write(ctx, msg, promise);
	        }
	    }	
	}

可以看读请求的数据时顺handler添加的顺序处理的，A-->B-->C
而写请求的处理是逆着添加顺序的，C-->B-->A

参考资料

netty in action
Netty 入门与实战：仿写微信 IM 即时通讯系统