netty

Handler在netty中，无疑占据着非常重要的地位。Handler与Servlet中的filter很像，通过Handler可以完成通讯报文的解码编码、拦截指定的报文、统一对日志错误进行处理、统一对请求进行计数、控制Handler执行与否。一句话，没有它做不到的只有你想不到的。

Netty中的所有handler都实现自ChannelHandler接口。按照输出输出来分，分为ChannelInboundHandler、ChannelOutboundHandler两大类。ChannelInboundHandler对从客户端发往服务器的报文进行处理，一般用来执行解码、读取客户端数据、进行业务处理等；ChannelOutboundHandler对从服务器发往客户端的报文进行处理，一般用来进行编码、发送报文到客户端。

Netty中，可以注册多个handler。ChannelInboundHandler按照注册的先后顺序执行；ChannelOutboundHandler按照注册的先后顺序逆序执行，如下图所示，按照注册的先后顺序对Handler进行排序，request进入Netty后的执行顺序为：





基本的概念就说到这，下面用一个例子来进行验证。该例子模拟Client与Server间的通讯，Server端注册了2个ChannelInboundHandler、2个ChannelOutboundHandler。当Client连接到Server后，会向Server发送一条消息。Server端通过ChannelInboundHandler 对Client发送的消息进行读取，通过ChannelOutboundHandler向client发送消息。最后Client把接收到的信息打印出来。

Server端一共有5个类：HelloServer InboundHandler1 InboundHandler2 OutboundHandler1 OutboundHandler2

1、HelloServer 代码如下

[java] view plaincopy





package com.guowl.testmultihandler;

import io.netty.bootstrap.ServerBootstrap;

import io.netty.channel.ChannelFuture;

import io.netty.channel.ChannelInitializer;

import io.netty.channel.ChannelOption;

import io.netty.channel.EventLoopGroup;

import io.netty.channel.nio.NioEventLoopGroup;

import io.netty.channel.socket.SocketChannel;

import io.netty.channel.socket.nio.NioServerSocketChannel;

public class HelloServer {

public void start(int port) throws Exception {

EventLoopGroup bossGroup = new NioEventLoopGroup();

EventLoopGroup workerGroup = new NioEventLoopGroup();

try {

ServerBootstrap b = new ServerBootstrap();

b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)

.childHandler(new ChannelInitializer() {

@Override

public void initChannel(SocketChannel ch) throws Exception {

// 注册两个OutboundHandler，执行顺序为注册顺序的逆序，所以应该是OutboundHandler2 OutboundHandler1

ch.pipeline().addLast(new OutboundHandler1());

ch.pipeline().addLast(new OutboundHandler2());

// 注册两个InboundHandler，执行顺序为注册顺序，所以应该是InboundHandler1 InboundHandler2

ch.pipeline().addLast(new InboundHandler1());

ch.pipeline().addLast(new InboundHandler2());

}

}).option(ChannelOption.SO_BACKLOG, 128)

.childOption(ChannelOption.SO_KEEPALIVE, true);

ChannelFuture f = b.bind(port).sync();

f.channel().closeFuture().sync();

} finally {

workerGroup.shutdownGracefully();

bossGroup.shutdownGracefully();

}

}

public static void main(String[] args) throws Exception {

HelloServer server = new HelloServer();

server.start(8000);

}

}

2、InboundHandler1

[java] view plaincopy





package com.guowl.testmultihandler;

import io.netty.channel.ChannelHandlerContext;

import io.netty.channel.ChannelInboundHandlerAdapter;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

public class InboundHandler1 extends ChannelInboundHandlerAdapter {

private static Logger logger = LoggerFactory.getLogger(InboundHandler1.class);

@Override

public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {

logger.info("InboundHandler1.channelRead: ctx :" + ctx);

// 通知执行下一个InboundHandler

ctx.fireChannelRead(msg);

}

@Override

public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {

logger.info("InboundHandler1.channelReadComplete");

ctx.flush();

}

}

3、InboundHandler2

[java] view plaincopy





package com.guowl.testmultihandler;

import io.netty.buffer.ByteBuf;

import io.netty.channel.ChannelHandlerContext;

import io.netty.channel.ChannelInboundHandlerAdapter;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

public class InboundHandler2 extends ChannelInboundHandlerAdapter {

private static Logger logger = LoggerFactory.getLogger(InboundHandler2.class);

@Override

// 读取Client发送的信息，并打印出来

public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {

logger.info("InboundHandler2.channelRead: ctx :" + ctx);

ByteBuf result = (ByteBuf) msg;

byte[] result1 = new byte[result.readableBytes()];

result.readBytes(result1);

String resultStr = new String(result1);

System.out.println("Client said:" + resultStr);

result.release();

ctx.write(msg);

}

@Override

public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {

logger.info("InboundHandler2.channelReadComplete");

ctx.flush();

}

}

4、OutboundHandler1

[java] view plaincopy





package com.guowl.testmultihandler;

import io.netty.buffer.ByteBuf;

import io.netty.channel.ChannelHandlerContext;

import io.netty.channel.ChannelOutboundHandlerAdapter;

import io.netty.channel.ChannelPromise;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

public class OutboundHandler1 extends ChannelOutboundHandlerAdapter {

private static Logger logger = LoggerFactory.getLogger(OutboundHandler1.class);

@Override

// 向client发送消息

public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {

logger.info("OutboundHandler1.write");

String response = "I am ok!";

ByteBuf encoded = ctx.alloc().buffer(4 * response.length());

encoded.writeBytes(response.getBytes());

ctx.write(encoded);

ctx.flush();

}

}

5、OutboundHandler2

[java] view plaincopy





package com.guowl.testmultihandler;

import io.netty.channel.ChannelHandlerContext;

import io.netty.channel.ChannelOutboundHandlerAdapter;

import io.netty.channel.ChannelPromise;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

public class OutboundHandler2 extends ChannelOutboundHandlerAdapter {

private static Logger logger = LoggerFactory.getLogger(OutboundHandler2.class);

@Override

public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {

logger.info("OutboundHandler2.write");

// 执行下一个OutboundHandler

super.write(ctx, msg, promise);

}

}

Client端有两个类：HelloClient HelloClientIntHandler

1、HelloClient

[java] view plaincopy





package com.guowl.testmultihandler;

import io.netty.bootstrap.Bootstrap;

import io.netty.channel.ChannelFuture;

import io.netty.channel.ChannelInitializer;

import io.netty.channel.ChannelOption;

import io.netty.channel.EventLoopGroup;

import io.netty.channel.nio.NioEventLoopGroup;

import io.netty.channel.socket.SocketChannel;

import io.netty.channel.socket.nio.NioSocketChannel;

public class HelloClient {

public void connect(String host, int port) throws Exception {

EventLoopGroup workerGroup = new NioEventLoopGroup();

try {

Bootstrap b = new Bootstrap();

b.group(workerGroup);

b.channel(NioSocketChannel.class);

b.option(ChannelOption.SO_KEEPALIVE, true);

b.handler(new ChannelInitializer() {

@Override

public void initChannel(SocketChannel ch) throws Exception {

ch.pipeline().addLast(new HelloClientIntHandler());

}

});

// Start the client.

ChannelFuture f = b.connect(host, port).sync();

f.channel().closeFuture().sync();

} finally {

workerGroup.shutdownGracefully();

}

}

public static void main(String[] args) throws Exception {

HelloClient client = new HelloClient();

client.connect("127.0.0.1", 8000);

}

}

2、HelloClientIntHandler

[java] view plaincopy





package com.guowl.testmultihandler;

import io.netty.buffer.ByteBuf;

import io.netty.channel.ChannelHandlerContext;

import io.netty.channel.ChannelInboundHandlerAdapter;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

public class HelloClientIntHandler extends ChannelInboundHandlerAdapter {

private static Logger logger = LoggerFactory.getLogger(HelloClientIntHandler.class);

@Override

// 读取服务端的信息

public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {

logger.info("HelloClientIntHandler.channelRead");

ByteBuf result = (ByteBuf) msg;

byte[] result1 = new byte[result.readableBytes()];

result.readBytes(result1);

result.release();

ctx.close();

System.out.println("Server said:" + new String(result1));

}

@Override

// 当连接建立的时候向服务端发送消息 ，channelActive 事件当连接建立的时候会触发

public void channelActive(ChannelHandlerContext ctx) throws Exception {

logger.info("HelloClientIntHandler.channelActive");

String msg = "Are you ok?";

ByteBuf encoded = ctx.alloc().buffer(4 * msg.length());

encoded.writeBytes(msg.getBytes());

ctx.write(encoded);

ctx.flush();

}

}

server端执行结果为：



在使用Handler的过程中，需要注意：

1、ChannelInboundHandler之间的传递，通过调用 ctx.fireChannelRead(msg) 实现；调用ctx.write(msg) 将传递到ChannelOutboundHandler。

2、ctx.write()方法执行后，需要调用flush()方法才能令它立即执行。

3、ChannelOutboundHandler 在注册的时候需要放在最后一个ChannelInboundHandler之前，否则将无法传递到ChannelOutboundHandler。