Netty笔记之三：Netty实现Socket编程

netty实现Tcp Socket编程。

demo实现功能
客户端向服务端发送消息，服务器接收到消息后向客户端响应。

加入依赖：

    io.netty
    netty-all
    4.1.10.Final

我是使用gradle构建项目的，所以build.gradle如下：

compile (
    'io.netty:netty-all:4.1.10.Final'
)

服务器代码

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.logging.LoggingHandler;

public class MyServer {
    public static void main(String[] args) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup wokerGroup = new NioEventLoopGroup();

        try{
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            //在服务器端的handler()方法表示对bossGroup起作用，而childHandler表示对wokerGroup起作用
            serverBootstrap.group(bossGroup,wokerGroup).channel(NioServerSocketChannel.class)
                    .childHandler(new MyServerInitializer());

            ChannelFuture channelFuture = serverBootstrap.bind(8899).sync();
            channelFuture.channel().closeFuture().sync();
        }finally {
            bossGroup.shutdownGracefully();
            wokerGroup.shutdownGracefully();
        }
    }
}

服务器端初始化Initializer

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.LengthFieldBasedFrameDecoder;
import io.netty.handler.codec.LengthFieldPrepender;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import io.netty.util.CharsetUtil;


public class MyServerInitializer extends ChannelInitializer{
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();

        pipeline.addLast(new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE,0,4,0,4));
        pipeline.addLast(new LengthFieldPrepender(4));
        //字符串解码
        pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
        //字符串编码
        pipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));
        //自己定义的处理器
        pipeline.addLast(new MyServerHandler());
    }
}

服务器端自定义Handler：

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

import java.util.UUID;

public class MyServerHandler extends SimpleChannelInboundHandler{

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        //打印出客户端地址
        System.out.println(ctx.channel().remoteAddress()+", "+msg);
        ctx.channel().writeAndFlush("form server: "+ UUID.randomUUID());
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

客户端：

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;

public class MyClient {
    public static void main(String[] args) throws Exception{
        EventLoopGroup eventLoopGroup = new NioEventLoopGroup();

        try{
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(eventLoopGroup).channel(NioSocketChannel.class)
                    .handler(new MyClientInitializer());

            ChannelFuture channelFuture = bootstrap.connect("localhost",8899).sync();
            channelFuture.channel().closeFuture().sync();
        }finally {
            eventLoopGroup.shutdownGracefully();
        }
    }
}

客户端初始化Initializer

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.LengthFieldBasedFrameDecoder;
import io.netty.handler.codec.LengthFieldPrepender;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import io.netty.util.CharsetUtil;

public class MyClientInitializer extends ChannelInitializer {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();

        pipeline.addLast(new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE,0,4,0,4));
        pipeline.addLast(new LengthFieldPrepender(4));
        pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
        pipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));
        pipeline.addLast(new MyClientHandler());
    }
}

客户端自定义Handler：

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

import java.time.LocalDateTime;


public class MyClientHandler extends SimpleChannelInboundHandler{

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        //服务端的远程地址
        System.out.println(ctx.channel().remoteAddress());
        System.out.println("client output: "+msg);
        ctx.writeAndFlush("from client: "+ LocalDateTime.now());
    }

    /**
     * 当服务器端与客户端进行建立连接的时候会触发，如果没有触发读写操作，则客户端和客户端之间不会进行数据通信，也就是channelRead0不会执行，
     * 当通道连接的时候，触发channelActive方法向服务端发送数据触发服务器端的handler的channelRead0回调，然后
     * 服务端向客户端发送数据触发客户端的channelRead0，依次触发。
     */
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ctx.writeAndFlush("来自与客户端的问题!");
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

启动客户端和服务端，服务端控制台：

/127.0.0.1:49645, 来自与客户端的问题!
/127.0.0.1:49645, from client: 2017-10-09T23:44:42.493
/127.0.0.1:49645, from client: 2017-10-09T23:44:42.495
/127.0.0.1:49645, from client: 2017-10-09T23:44:42.496
...

客户端控制台：

localhost/127.0.0.1:8899
client output: form server: ca79614c-351c-4aed-9906-532fb19f8286
localhost/127.0.0.1:8899
client output: form server: c66482ff-503b-41e8-a2b1-0de88e856433
localhost/127.0.0.1:8899
...

流程分析：
当客户端和服务端通道建立连接的时候（触发channelActive方法），客户端向服务发送来“自与客户端的问题!”数据，服务器端channelRead0被触发，进行回写数据到客户端触发客户端的channelRead0回调方法被调用，依次往复。