Netty之入门案例

 前面给大家介绍了NIO，我们会发现用NIO实现异步非阻塞的网络通信代码量非常大，而且并不是很好理解，在实际的开发中一般我们也都是会实现基于NIO的框架来操作的，比如Netty，这样开发效率有高而且Bug也少。

Netty入门案例

官网:https://netty.io/

环境准备

 你可以去官网下载对应的jar包依赖，然后创建普通的java项目即可，也可以跟着我通过创建maven项目来实现，如下是会用到的依赖

<dependencies>
    <dependency>
        <groupId>io.netty</groupId>
        <artifactId>netty-all</artifactId>
        <version>5.0.0.Alpha2</version>
    </dependency>

    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-log4j12</artifactId>
        <version>1.7.25</version>
    </dependency>
</dependencies>      

log4j.properties属性文件

log4j.rootCategory=info, stdout , R
 
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=[QC] %p [%t] %C.%M(%L) | %m%n
 
log4j.appender.R=org.apache.log4j.DailyRollingFileAppender
log4j.appender.R.File=C:\\Tomcat 5.5\\logs\\qc.log
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%d-[TS] %p %t %c - %m%n      

服务端

TimerServer

package com.dpb.netty.demo;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;

public class TimerServer {

    public void bind(int port) throws Exception{
        // 配置服务端的NIO线程组
        // 服务端接受客户端的连接
        NioEventLoopGroup bossGroup = new NioEventLoopGroup();
        // 进行SocketChannel的网络读写
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();
        
        try {
            // 用于启动NIO服务端的辅助启动类，目的是降低服务端的开发复杂度
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup,workerGroup)
            // 设置Channel
            .channel(NioServerSocketChannel.class)
            // 设置TCP参数
            .option(ChannelOption.SO_BACKLOG, 1024)
            // 绑定I/O事件的处理类ChildChannelHandler
            .childHandler(new ChildChannelHandler());
        
        // 绑定端口，同步等待成功
        ChannelFuture f = b.bind(port).sync();
        // 等待服务端监听端口关闭
        f.channel().closeFuture().sync();
        } finally {
            // 优雅退出，释放线程池资源
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
        
    }
    
    private class ChildChannelHandler extends ChannelInitializer<SocketChannel>{

        @Override
        protected void initChannel(SocketChannel arg0) throws Exception {
            arg0.pipeline().addLast(new TimerServerHandler());
            
        }
        
    }
    
    public static void main(String[] args) throws Exception {
        int port = 8080;
        new TimerServer().bind(port);
    }
}
      

TimerServerHandler

package com.dpb.netty.demo;

import java.nio.ByteBuffer;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
/**
 * 用于对网络事件进行读写操作
 * @author 波波烤鸭
 * @email [email protected]
 *
 */
public class TimerServerHandler extends ChannelHandlerAdapter{

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        // ByteBuf 类似于NIO中的java.nio.ByteBuffer对象，
        ByteBuf buf = (ByteBuf) msg;
        byte[] req = new byte[buf.readableBytes()];
        buf.readBytes(req);
        String body = new String(req,"utf-8");
        System.out.println("The time server receive order : "+body);
        String currentTime = "Query time order".equalsIgnoreCase(body)?new java.util.Date(System.currentTimeMillis()).toString():"BAD ORDER";
        ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
        ctx.write(resp);
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        // TODO Auto-generated method stub
        ctx.flush();
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        // TODO Auto-generated method stub
        ctx.close();
    }
}      

客户端

TimeClient

package com.dpb.netty.demo;

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 TimeClient {
    
    public static void main(String[] args) throws Exception {
        int port = 8080;
        new TimeClient().connect(port, "127.0.0.1");
    }

    public void connect(int port,String host)throws Exception{
        // 配置客户端NIO线程组
        EventLoopGroup group = new NioEventLoopGroup();
        try{
            Bootstrap b = new Bootstrap();
            b.group(group).channel(NioSocketChannel.class)
                .option(ChannelOption.TCP_NODELAY, true)
                .handler(new ChannelInitializer<SocketChannel>() {

                    @Override
                    protected void initChannel(SocketChannel arg0) throws Exception {
                        arg0.pipeline().addLast(new TimeClientHandler());
                    }
                    
                });
            // 发起异步连接操作
            ChannelFuture f = b.connect(host,port).sync();
            // 等待客户端链路关闭
            f.channel().closeFuture().sync();
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            // 优雅退出，释放NIO线程组
            group.shutdownGracefully();
        }
    }
}      

TimeClientHandler

package com.dpb.netty.demo;

import java.util.logging.Logger;

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

public class TimeClientHandler extends ChannelHandlerAdapter{

    private static final Logger logger = Logger.getLogger(TimeClientHandler.class.getName());
    
    private final ByteBuf firstMessage;
    
    public TimeClientHandler(){
        byte[] req = "Query time order".getBytes();
        firstMessage = Unpooled.buffer(req.length);
        firstMessage.writeBytes(req);
    }
    
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ctx.writeAndFlush(firstMessage);
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf buf = (ByteBuf) msg;
        byte[] req  = new  byte[buf.readableBytes()];
        buf.readBytes(req);
        String body = new String(req,"UTF-8");
        System.out.println("Now is :"+body);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        // TODO Auto-generated method stub
        logger.warning("Unexpected exception from downstream:"+cause.getMessage());
        ctx.close();
    }
}      

测试

 先启动服务器，再启动客户端，输出如下:

The time server receive order : Query time order      

Now is :Thu Apr 11 22:22:58 CST 2019      

总结

 通过案例使用Netty实现了客户端和服务器的通信，可以发现相比传统的NIO程序，Netty的代码更加简洁，开发难度更低，扩展性也更好，非常适合作为基础通信框架被用户集成和使用