[pravega-022] pravega源码分析--Controller子项目--关于netty[02]-优快云博客

本文详细介绍了一个基于Netty的Echo服务实现，包括server和client两端的代码结构和功能实现。通过具体示例，深入理解Netty框架的核心要素，如线程模型、管道和处理器等。

1.一个netty echo服务的例子。client向server发消息，server向client返回同样的消息。程序分两部分，server项目和client项目。这里包含了netty的核心要素。更多的细节请参考前文提到的参考资料即可。

2.server项目

2.1 目录结构

├── build.gradle
├── settings.gradle
└── src
├── main
├── java
├── EchoServerHandler.java
└── Main.java
2.2 build.gradle文件内容

group 'com.brian.demo.netty'
version '1.0-SNAPSHOT'

apply plugin: 'java'

sourceCompatibility = 1.8

repositories {
    mavenCentral()
}

dependencies {
    compile group: 'io.netty', name: 'netty-all', version: '4.1.12.Final'
    testCompile group: 'junit', name: 'junit', version: '4.12'
}

2.3 Main.java文件内容

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
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 java.net.InetSocketAddress;

//主要参考资料：
// 《netty in action》
// https://github.com/waylau/essential-netty-in-action
public class Main {
    private final int port;

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

    public static void main(String args[]) throws Exception {
        new Main(8008).start();
    }

    public void start() throws Exception {
        //NioEventLoopGroup是一个线程池，一个线程可以处理多个channel，一个channel只对应一个线程
        EventLoopGroup group = new NioEventLoopGroup();
        //echo服务handler
        final EchoServerHandler echoServerHandler = new EchoServerHandler();

        //创建 引导服务器
        ServerBootstrap sbs = new ServerBootstrap();
        try {
            //设置线程池
            sbs.group(group)
                    //指定NIO传输的channel
                    .channel(NioServerSocketChannel.class)
                    //本地端口
                    .localAddress(new InetSocketAddress(port))
                    //配置handler pipeline。每个channel有一个pipline，
                    // 包含多个handler，事件从pipline逐个经过handler进行处理。
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(echoServerHandler);
                        }
                    });
            //绑定服务器，然后同步等待服务器关闭。
            ChannelFuture future = sbs.bind().sync();
            System.out.println(Main.class.getName() +
                    " started and listening for connections on " + future.channel().localAddress());
            //关闭channel，同步等待
            future.channel().closeFuture().sync();
        } finally {
            //释放线程池
            group.shutdownGracefully().sync();
        }
    }
}

2.4 EchoServerHandler.java文件内容

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 io.netty.util.CharsetUtil;

//Sharable注解，声明这个Handler的实例可以被多个channel共享使用
@ChannelHandler.Sharable
//ChannelInboundHandler接口，处理入站事件
public class EchoServerHandler extends ChannelInboundHandlerAdapter {

    //每个信息入站都会调用channelRead
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg){
        //收到的消息是Object msg，强转撑ByteBuf
        ByteBuf inBuf = (ByteBuf)msg;
        //在控制台输出接收到的消息
        System.out.println("Server received:" + inBuf.toString(CharsetUtil.UTF_8));
        //再把消息不做修改重新写给客户端。注意，此时数据还没有flush，仍然在服务端。
        ctx.write(inBuf);
    }

    //通知处理器，当下的channelread()读取消息是本批处理的最后一条消息的时候，调用本函数
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        //把所有数据冲刷flush到客户端，关闭通道。至此操作完成。Listern以future方式通知操作完成。
        ctx.writeAndFlush(Unpooled.EMPTY_BUFFER)
                .addListener(ChannelFutureListener.CLOSE);
    }

    //读操作遇到异常
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

3. Client项目

3.1 文件目录结构

.
├── build.gradle
├── settings.gradle
└── src
├── main
├── java
   ├── EchoClientHandler.java
   └── Main.java

3.2 build.gradle文件内容

group 'com.brian.demo.netty'
version '1.0-SNAPSHOT'

apply plugin: 'java'

sourceCompatibility = 1.8

repositories {
    mavenCentral()
}

dependencies {
    compile group: 'io.netty', name: 'netty-all', version: '4.1.12.Final'
    testCompile group: 'junit', name: 'junit', version: '4.12'
}

3.3 Main.java文件内容

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
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 java.net.InetSocketAddress;

public class Main {
    private final String host;
    private final int port;

    public Main(){
        this.host="127.0.0.1";
        this.port=8008;
    }

    public void start() throws Exception{
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group).channel(NioSocketChannel.class)
                    .remoteAddress(new InetSocketAddress(host,port))
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                          ch.pipeline().addLast(new EchoClientHandler());
                        }
                    });
            ChannelFuture future = b.connect().sync();
            future.channel().closeFuture().sync();
        }finally {
            group.shutdownGracefully();
        }
    }

    public static void main(String args[])throws Exception{
        new Main().start();
    }
}

3.4 EchoClientHandler.java文件内容

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.util.CharsetUtil;

@ChannelHandler.Sharable
public class EchoClientHandler extends SimpleChannelInboundHandler<ByteBuf> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
        System.out.println("client received:" + msg.toString(CharsetUtil.UTF_8));
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ctx.writeAndFlush(Unpooled.copiedBuffer("hello,world", CharsetUtil.UTF_8));
    }

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

4. 如果遇到gradle不能导入nettty包的情况，关闭项目，删除~/.gradle目录所有文件，然后重新在idea做import项目即可。