Netty快速学习3-第一个测试实例

记录 netty 的 hello world 级实例代码

说明
服务端
- 启动主体程序 serverBootstrap
- 服务端 Channel 处理器
- 快速测试服务端
客户端
- 启动主体程序 bootstrap
- 客户端 Channel 处理器
- 快速测试客户端
简要说明 EventLoop

说明

几乎所有的学习netty资料都是以一个 Echo 程序为开始，
所谓Echo程序：就是应答服务，客户端传递什么消息服务端原封不动的返回给客户端。

Echo程序包含服务端代码和客户端代码， Netty的服务端客户端的代码几乎定死的框架结构。

服务端启动主体程序 serverBootstrap

package org.example.netty;

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;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


public class EchoServer {

    static Logger logger = LoggerFactory.getLogger(EchoServer.class);
    private int port;

    public EchoServer(int port) {
        this.port = port;
    }

    
    public void run() throws InterruptedException {

        //配置服务端线程组
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup, workGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 1024)
                    .childHandler(new ChannelInitializer() {
                        @Override
                        protected void initChannel(SocketChannel ch) {
                            ch.pipeline().addLast(new EchoServerHandler());
                        }
                    });

            logger.info(">>>>>>>>>>>Echo 服务端启动...");
            //绑定端口，同步等待成功
            ChannelFuture channelFuture = serverBootstrap.bind(port).sync();

            //等待服务端监听端口关闭
            channelFuture.channel().closeFuture().sync();
            logger.info(">>>>>>>>>>>Echo 服务端关闭！");

        } finally {

            //优雅退出，释放线程池
            workGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }


    public static void main(String[] args) throws InterruptedException {
        int port = 8081;
        if (args.length > 0) {
            port = Integer.parseInt(args[0]);
        }
        new EchoServer(port).run();
    }

}

服务端 Channel 处理器

package org.example.netty;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.nio.charset.Charset;


@ChannelHandler.Sharable
public class EchoServerHandler extends ChannelInboundHandlerAdapter {
    static Logger logger = LoggerFactory.getLogger(EchoServerHandler.class);

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) {

        ByteBuf data = (ByteBuf) msg;

        logger.info(">>>>>>>>>>>EchoServerHandle 收到数据: {}", data.toString(Charset.forName("GBK")));
        ctx.writeAndFlush(data);
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) {
        logger.info(">>>>>>>>>>>EchoServerHandle 接受完毕！");
        ctx.writeAndFlush(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE);
        logger.info(">>>>>>>>>>>EchoServerHandle 关闭！");
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        logger.error(">>>>>>>>>>>EchoServerHandle 异常 ", cause);
        ctx.close();
    }


    @Override
    public void channelRegistered(ChannelHandlerContext ctx) {
        logger.info("EchoServerHandle channelRegistered");
    }

    @Override
    public void channelUnregistered(ChannelHandlerContext ctx) {
        logger.info("EchoServerHandle channelUnregistered");
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        logger.info("EchoServerHandle channelActive");
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) {
        logger.info("EchoServerHandle channelInactive");
    }
}

快速测试服务端

window 打开Dos命令行窗口：
输入 telnet localhost 8081 看是否能进入。
然后观察后台服务端控制台日志信息：

此时随便输入一个字母例如：A 连接将中断，服务端控制台打印：

21:21:21.109 [nioEventLoopGroup-3-5] INFO org.example.netty.EchoServerHandler - >>>>>>>>>>>EchoServerHandle 收到数据: A
21:21:21.109 [nioEventLoopGroup-3-5] INFO org.example.netty.EchoServerHandler - >>>>>>>>>>>EchoServerHandle 接受完毕！
21:21:21.110 [nioEventLoopGroup-3-5] INFO org.example.netty.EchoServerHandler - >>>>>>>>>>>EchoServerHandle 关闭！
21:21:21.110 [nioEventLoopGroup-3-5] INFO org.example.netty.EchoServerHandler - EchoServerHandle channelInactive
21:21:21.110 [nioEventLoopGroup-3-5] INFO org.example.netty.EchoServerHandler - EchoServerHandle channelUnregistered

连接之所以立刻关闭，主要是因为，服务端设置了：

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) {
        logger.info(">>>>>>>>>>>EchoServerHandle 接受完毕！");
        ctx.writeAndFlush(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE);
        logger.info(">>>>>>>>>>>EchoServerHandle 关闭！");
    }

客户端启动主体程序 bootstrap

package org.example.netty;

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;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.net.InetSocketAddress;

public class EchoClient {
    static Logger logger = LoggerFactory.getLogger(EchoClient.class);
    private String host;

    private int port;

    public EchoClient(String host, int port) {
        this.host = host;
        this.port = port;
    }

    public void start() throws InterruptedException {

        EventLoopGroup group = new NioEventLoopGroup();
        try {

            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group)

                    .channel(NioSocketChannel.class)

                    .remoteAddress(new InetSocketAddress(host, port))
                    .option(ChannelOption.TCP_NODELAY, true)
                    .handler(new ChannelInitializer() {
                        @Override
                        protected void initChannel(SocketChannel ch) {
                            ch.pipeline().addLast(new EchoClientHandler());
                        }
                    });

            //连接到服务端，connect是异步连接，在调用同步等待sync，等待连接成功
            ChannelFuture channelFuture = bootstrap.connect().sync();
            logger.info(">>>>>>>>>>>Echo 客户端启动...");

            //阻塞直到客户端通道关闭
            channelFuture.channel().closeFuture().sync();
            logger.info(">>>>>>>>>>>Echo 客户端关闭！");
        } finally {
            //优雅退出，释放NIO线程组
            group.shutdownGracefully();
        }

    }

    public static void main(String[] args) throws InterruptedException {
        new EchoClient("127.0.0.1", 8081).start();
    }

}

客户端 Channel 处理器

package org.example.netty;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.nio.charset.Charset;


public class EchoClientHandler extends SimpleChannelInboundHandler {

    static Logger logger = LoggerFactory.getLogger(EchoClientHandler.class);

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) {

        logger.info(">>>>>>>>>>>EchoClientHandler 接受到数据: {}", msg.toString(Charset.forName("GBK")));

    }


    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        logger.info(">>>>>>>>>>>Active");
        ctx.writeAndFlush(Unpooled.copiedBuffer(
                "hello,这是客户端发出的echo消息", Charset.forName("GBK")));
    }


    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) {
        logger.info(">>>>>>>>>>>EchoClientHandler channelReadComplete");
    }


    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        logger.error(">>>>>>>>>>>EchoClientHandler 异常 ", cause);
        ctx.close();
    }
}

快速测试客户端

运行客户端main方法：
客户端控制台打印：

同时服务端控制台打印：

简要说明 EventLoop

1个 EventLoop 类似一个线程，
1个 Channel 就是一个客户端和服务端的连接通道（看成一个TCP长连接）
1个EventLoop 可以服务多个Channel
1个Channel 只对应一个EventLoop

可以创建多个 EventLoop 来优化资源利用，也就是EventLoopGroup
EventLoopGroup 负责分配 EventLoop 到新创建的 Channel，里面包含多个EventLoop。

回顾一下多线程Reactor模型：

Netty快速学习3-第一个测试实例

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