《Netty权威指南》之netty初体验

最新推荐文章于 2022-09-06 14:21:37 发布

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本文介绍使用Netty框架快速搭建时间服务器的过程，仅需40行代码即可实现。Netty简化了网络编程复杂性，通过NioEventLoopGroup管理线程，ServerBootstrap配置服务器参数，ChannelInitializer设置处理器。具体业务代码展示了如何读写数据，处理异常。

通过NIO的方式搭建一个时间服务器有很繁杂的过程，而netty则只需要很简单的程序就能搞定，而且netty的编程模式很固定，客户端程序员只需要在网络配置的地方和业务逻辑的地方写自己的代码即可

package com.lyzx.netty;

import io.netty.bootstrap.Bootstrap;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import org.junit.Test;

/**
 * @author hero.li
 * 第一个Netty程序
 */
public class Netty01 {

    @Test
    public void nettyServer() throws InterruptedException{
        //开启两个线程组，一个用于接受客户端的请求   另一个用于异步的网络IO的读写
        NioEventLoopGroup bossGroup = new NioEventLoopGroup();
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();

        //Netty启动的辅助类 里面封装了客户端和服务端的链接以及如何处理选择器 selector等逻辑
        ServerBootstrap b = new ServerBootstrap();

        //传入两个线程组,设置传输块大小为1k，
        //添加ServerHandler类型的过滤器(表示如何处理这些消息，
        //过滤器当然要集成netty的一个接口)
        b.group(bossGroup,workerGroup)
                .channel(NioServerSocketChannel.class)
                .option(ChannelOption.SO_BACKLOG,1024)
                .childHandler(new ChannelInitializer<SocketChannel>(){
                    @Override
                    protected void initChannel(SocketChannel socketChannel) throws Exception {
                        socketChannel.pipeline().addLast(new ServerHandler());
                    }
                });

        //同步等待绑定端口结束
        ChannelFuture f = b.bind(9988).sync();
        //等待服务端监听端口关闭
        f.channel().closeFuture().sync();
        //优雅的关闭线程组
        bossGroup.shutdownGracefully();
        workerGroup.shutdownGracefully();
    }

    @Test
    public void nettyClient() throws InterruptedException {
        NioEventLoopGroup group = new NioEventLoopGroup();
        Bootstrap b = new Bootstrap();
        b.group(group)
                .channel(NioSocketChannel.class)
                .option(ChannelOption.TCP_NODELAY,true)
                .handler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception{
                        ch.pipeline().addLast(new ClientHandler());
                    }
                });

        ChannelFuture f = b.connect("127.0.0.1", 9988).sync();
        f.channel().closeFuture().sync();
        group.shutdownGracefully();
    }
}

只需要40行就可以搞定一个时间服务器的框架，其余的就需要根据具体的业务写业务代码即可，具体的业务代码如下

package com.lyzx.netty;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;


/**
 * 对于网事件做读写，通常只要关注channelRead()和exceptionCaught()即可
 */
public class ServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println("server:channelRead 通道可读开始");
        //从msg对象中获取消息并打印
        ByteBuf bytebuf = (ByteBuf)msg;
        byte[] bytes = new byte[bytebuf.readableBytes()];
        bytebuf.readBytes(bytes);
        System.out.println("收到的消息:"+new String(bytes,"UTF-8"));

        //获取当前的时间并通过ctx的write方法异步写数据到SocketChannel
        //ctx.write并不会直接把数据写入到缓冲区等到调用channelReadComplete里面的ctx.flush()
        //的时候再把数写入到SocketChannel
        String datetime = LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss:SSS"));
        ByteBuf byteBuf = Unpooled.copiedBuffer(datetime.getBytes("UTF-8"));
        ctx.writeAndFlush(byteBuf);
        System.out.println("server:channelRead 通道可读结束");
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        System.out.println("server:channelReadComplete 通道可读完成 ");
        ctx.flush();
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        System.out.println("server:exceptionCaught 发生异常");
        ctx.close();
    }
}

package com.lyzx.netty;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

public class ClientHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("client:channelActive  通道激活开始");
        ByteBuf buff  = Unpooled.copiedBuffer("11".getBytes("UTF-8"));
        ctx.writeAndFlush(buff);
        System.out.println("client:channelActive  通道激活结束");
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx,Object msg) throws Exception {
        System.out.println("client:通道可读开始");
        ByteBuf buf = (ByteBuf)msg;
        byte[] bytes = new byte[buf.readableBytes()];
        buf.readBytes(bytes);
        System.out.println("response time :"+new String(bytes));
        System.out.println("client:通道可读结束");
    }

    /**
     * 类似于AOP的后置通知 在这里当通道读取完毕后关闭通道
     * @param ctx
     * @throws Exception
     */
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        System.out.println("client:通道可读完成");
        ctx.channel().close();
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        System.out.println("client:发生异常");
        super.exceptionCaught(ctx, cause);
    }
}