《精通并发与Netty》学习笔记（03 - 客户端程序编写）

上节我们编写了netty服务端的程序，这节我们来写客户端程序

第一步：改造服务端程序为：

（1）MyServer类：

package com.ssy.netty.demo01;

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;

/**
 * netty作为长连接的服务器基于websoket，实现客户端与服务器端长连接。
 */
public class MyServer {
    public static void main(String[] args) {
        //负责接收客户端连接
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        //处理连接
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup,workerGroup) // 绑定线程池
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new MyServerInitializer());

            //绑定端口号
            ChannelFuture channelFuture = serverBootstrap.bind(8888).sync();
            channelFuture.channel().closeFuture().sync();
        } catch (Exception e) {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

（2）MyServerInitializer类

package com.ssy.netty.demo01;

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.http.HttpServerCodec;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import io.netty.util.CharsetUtil;

/**
 * 绑定客户端连接时候触发操作
 */
public class MyServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        //负载http 请求编码解码
        //pipeline.addLast("httpServerCodec",new HttpServerCodec());
        //实际处理请求
        //pipeline.addLast("httpServerHandler",new HttpServerHandler());
        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 MyServerHandler());
    }
}

（3）MyServerHandler类

package com.ssy.netty.demo01;

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

import java.time.LocalDateTime;

public class MyServerHandler extends SimpleChannelInboundHandler<String> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        System.out.println(ctx.channel().remoteAddress());
        System.out.println("client output:"+msg);
        ctx.writeAndFlush("from server:" + LocalDateTime.now());
    }

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

编写客户端主程序MyClient

package com.ssy.netty.demo01;

import io.netty.bootstrap.Bootstrap;
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.NioSocketChannel;

public class MyClient {
    public static void main(String[] args) {
        EventLoopGroup eventLoopGroup = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(eventLoopGroup) // 绑定线程池
                    .channel(NioSocketChannel.class)
                    .handler(new MyClientInitializer());

            //绑定端口号
            ChannelFuture channelFuture = bootstrap.connect("localhost",8888).sync();
            channelFuture.channel().closeFuture().sync();
        } catch (Exception e) {
            eventLoopGroup.shutdownGracefully();
        }
    }
}

第二步：编写MyClientInitializer

package com.ssy.netty.demo01;

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<SocketChannel> {
    @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());
    }
}

第三步：编写MyClientHandler

package com.ssy.netty.demo01;

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

import java.time.LocalDateTime;

public class MyClientHandler extends SimpleChannelInboundHandler<String> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        System.out.println(ctx.channel().remoteAddress());
        System.out.println("client output:"+msg);
        ctx.writeAndFlush("from client:" + LocalDateTime.now());
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ctx.writeAndFlush("来自客户端的问候");
    }

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

分别启动MyServer程序和MyClient程序，客户端成功调用服务端。

到此为止，我们已经完成了简单的netty服务端与客户端的通信程序，下节我们会对谷歌的Google Protobuf做一次详解，敬请期待吧！