Netty之入門案例

 前面給大家介紹了NIO，我們會發現用NIO實作異步非阻塞的網絡通信代碼量非常大，而且并不是很好了解，在實際的開發中一般我們也都是會實作基于NIO的架構來操作的，比如Netty，這樣開發效率有高而且Bug也少。

Netty入門案例

官網:https://netty.io/

環境準備

 你可以去官網下載下傳對應的jar包依賴，然後建立普通的java項目即可，也可以跟着我通過建立maven項目來實作，如下是會用到的依賴

<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屬性檔案

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      

服務端

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{
        // 配置服務端的NIO線程組
        // 服務端接受用戶端的連接配接
        NioEventLoopGroup bossGroup = new NioEventLoopGroup();
        // 進行SocketChannel的網絡讀寫
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();
        
        try {
            // 用于啟動NIO服務端的輔助啟動類，目的是降低服務端的開發複雜度
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup,workerGroup)
            // 設定Channel
            .channel(NioServerSocketChannel.class)
            // 設定TCP參數
            .option(ChannelOption.SO_BACKLOG, 1024)
            // 綁定I/O事件的處理類ChildChannelHandler
            .childHandler(new ChildChannelHandler());
        
        // 綁定端口，同步等待成功
        ChannelFuture f = b.bind(port).sync();
        // 等待服務端監聽端口關閉
        f.channel().closeFuture().sync();
        } finally {
            // 優雅退出，釋放線程池資源
            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;
/**
 * 用于對網絡事件進行讀寫操作
 * @author 波波烤鴨
 * @email [email protected]
 *
 */
public class TimerServerHandler extends ChannelHandlerAdapter{

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        // ByteBuf 類似于NIO中的java.nio.ByteBuffer對象，
        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();
    }
}      

用戶端

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{
        // 配置用戶端NIO線程組
        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());
                    }
                    
                });
            // 發起異步連接配接操作
            ChannelFuture f = b.connect(host,port).sync();
            // 等待用戶端鍊路關閉
            f.channel().closeFuture().sync();
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            // 優雅退出，釋放NIO線程組
            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();
    }
}      

測試

 先啟動伺服器，再啟動用戶端，輸出如下:

The time server receive order : Query time order      

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

總結

 通過案例使用Netty實作了用戶端和伺服器的通信，可以發現相比傳統的NIO程式，Netty的代碼更加簡潔，開發難度更低，擴充性也更好，非常适合作為基礎通信架構被使用者內建和使用