[pravega-022] pravega源码分析--Controller子项目--关于netty[02]

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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 = 1.8repositories {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handlerfinal 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>() {@Overridepublic 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@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg){//收到的消息是Object msg，强转撑ByteBufByteBuf 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@Overridepublic 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@Overridepublic 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 = 1.8repositories {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>() {@Overrideprotected 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> {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {System.out.println("client received:" + msg.toString(CharsetUtil.UTF_8));}@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {ctx.writeAndFlush(Unpooled.copiedBuffer("hello,world", CharsetUtil.UTF_8));}@Overridepublic 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。
   
   

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