Netty入门之创建Maven多模块依赖项目

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新学Netty，编译运行时踩了一些坑，记录在此。
essential netty in action中有一个入门demo，EchoServer and EchoClient，用于Netty入门的小demo。
(Essential Netty in Action)

EchoClient主要功能

1、启动客户端，发起连接

public class Client {    private final String host;    private final int port;    public Client(String host, int port) {        this.host = host;        this.port = port;    }    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                public void initChannel(SocketChannel ch)                             throws Exception {                    ch.pipeline().addLast(new ClientHandler());                }            });            ChannelFuture f = b.connect().sync();            f.channel().closeFuture().sync();        }finally {            group.shutdownGracefully().sync();        }    }    public static void main(String[] args) throws Exception {        if(args.length != 2){            System.err.println(                    "Usage :" + Client.class.getSimpleName()+                    "<host><port>"                    );            return;        }        final String host = args[0];        final int port = Integer.parseInt(args[1]);        new Client(host,port).start();    }}

2、ClientHandler处理返回到客户端的数据

class ClientHandler extends SimpleChannelInboundHandler<ByteBuf>{    @Override    public void channelActive(ChannelHandlerContext ctx){        ctx.writeAndFlush(Unpooled.copiedBuffer("Netty rocks!",CharsetUtil.UTF_8));    }    @Override    protected void channelRead0(ChannelHandlerContext ctx, ByteBuf in) throws Exception {        System.out.println("Client received: "+in.toString(CharsetUtil.UTF_8));     }    @Override    public void exceptionCaught(ChannelHandlerContext ctx,                    Throwable cause) {        cause.printStackTrace();        ctx.close();    }}

EchoServer主要功能

1、启动服务端，监听连接请求

public class EchoServer {    public void bind(int port) throws Exception {        //配置服务端的NIO线程组        //实际上EventLoopGroup就是Reactor线程组        //两个Reactor一个用于服务端接收客户端的连接，另一个用于进行SocketChannel的网络读写        EventLoopGroup bossGroup = new NioEventLoopGroup();        EventLoopGroup workerGroup = new NioEventLoopGroup();        try{            /**             * 由于我们使用在 NIO 传输，我们                已指定 NioEventLoopGroup接受和处理新连接，指定 NioServerSocketChannel                为信道类型。在此之后，我们设置本地地址是 InetSocketAddress 与所选择的端口（6）如。                服务器将绑定到此地址来监听新的连接请求。             */            //ServerBootstrap对象是Netty用于启动NIO服务端的辅助启动类，目的是降低服务端开发的复杂度            ServerBootstrap b = new ServerBootstrap();            //Set the EventLoopGroup for the parent (acceptor) and the child (client).             b.group(bossGroup, workerGroup)                .channel(NioServerSocketChannel.class)                .localAddress(new InetSocketAddress(port))                //绑定I/O事件的处理类ChildChannelHandler,作用类似于Reactor模式中的Handler类                //主要用于处理网络I/O事件，例如记录日志，对消息进行编解码等                .childHandler(new ChannelInitializer<SocketChannel>(){                //添加ServerHandler到Channel的ChannelPipeline                    //通过ServerHandler给每一个新来的Channel初始化                    @Override                    protected void initChannel(SocketChannel ch) throws Exception {                        ch.pipeline().addLast(new ServerHandler());                    }                });            //绑定监听端口，调用sync同步阻塞方法等待绑定操作完成，完成后返回ChannelFuture类似于JDK中Future            ChannelFuture f = b.bind(port).sync();            //使用sync方法进行阻塞，等待服务端链路关闭之后Main函数才退出            f.channel().closeFuture().sync();        }finally {            //优雅退出，释放线程池资源            bossGroup.shutdownGracefully();            workerGroup.shutdownGracefully();        }    }    public static void main(String[] args) throws Exception {        int port = 8080;        if(args != null && args.length > 0) {            try {                port = Integer.valueOf(args[0]);            }catch (NumberFormatException e) {                //采用默认值            }        }        new Server().bind(port);    }}

2、ServerHandler处理发送到服务端的数据

private class ServerHandler extends ChannelInboundHandlerAdapter {        //每个信息入站都会调用        @Override        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {            ByteBuf buf = (ByteBuf) msg;            System.out.println("The server receive msg :" + buf.toString());            ctx.write(buf);        }        //通知处理器最后的channelread()是当前批处理中的最后一条消息时调用        @Override        public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {            ctx.flush();        }        //读操作时捕获到异常时调用        @Override        public void exceptionCaught (ChannelHandlerContext ctx, Throwable cause) {            ctx.close();        }    }

在Eclipse中使用maven构建该demo

首先分析该项目中的模块及其依赖关系。
这个项目中有两个模块，Server与Client，它们的依赖库相同，互相之间没有依赖关系。
1、创建包含这两个模块的父项目netty-parent，pom.xml文件配置

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">  <modelVersion>4.0.0</modelVersion>  <groupId>netty</groupId>  <artifactId>netty-parent</artifactId>  <version>0.0.1-SNAPSHOT</version>  <name>netty-parent</name>  <!--父项目必须包含该标签-->  <packaging>pom</packaging>  <!-- 引入netty依赖-->   <dependencies>       <dependency>           <groupId>junit</groupId>           <artifactId>junit</artifactId>           <version>4.10</version>           <scope>test</scope>       </dependency>       <dependency>           <groupId>org.slf4j</groupId>           <artifactId>slf4j-simple</artifactId>           <version>1.6.4</version>           <scope>compile</scope>       </dependency>       <dependency>           <groupId>io.netty</groupId>           <artifactId>netty-all</artifactId> <!-- Use 'netty-all' for 4.0 or above -->           <version>4.1.10.Final</version>           <scope>compile</scope>       </dependency>   </dependencies>  </project>

2、以netty-parent为parent project创建新的maven module，分别为netty-client和netty-server，创建完毕之后工程结构如图所示
这里写图片描述
3、netty-server的pom.xml文件配置为

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">  <modelVersion>4.0.0</modelVersion>  <!--在eclipse中创建module时自动生成-->  <parent>    <groupId>netty</groupId>    <artifactId>netty-parent</artifactId>    <version>0.0.1-SNAPSHOT</version>  </parent>  <artifactId>netty-server</artifactId>  <!--子module的打包形式-->  <packaging>jar</packaging>  <name>netty-server</name></project>

4、netty-client的pom.xml文件配置为

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">  <modelVersion>4.0.0</modelVersion>  <parent>    <groupId>netty</groupId>    <artifactId>netty-parent</artifactId>    <version>0.0.1-SNAPSHOT</version>  </parent>  <artifactId>netty-client</artifactId>  <packaging>jar</packaging>  <name>netty-client</name></project>

5、编译项目并运行Server和Client
5.1 在命令行中进入netty-parent项目目录，运行命令编译项目

D:\workspace\netty-parent>mvn package[INFO] Scanning for projects...[INFO] ------------------------------------------------------------------------[INFO] Reactor Build Order:[INFO][INFO] netty-parent[INFO] netty-client[INFO] netty-server[INFO][INFO] ------------------------------------------------------------------------[INFO] Building netty-parent 0.0.1-SNAPSHOT[INFO] ------------------------------------------------------------------------[INFO][INFO] ------------------------------------------------------------------------[INFO] Building netty-client 0.0.1-SNAPSHOT[INFO] ------------------------------------------------------------------------…………省略[INFO] ------------------------------------------------------------------------[INFO] Building netty-server 0.0.1-SNAPSHOT…………省略[INFO] Reactor Summary:[INFO][INFO] netty-parent ....................................... SUCCESS [  0.002 s][INFO] netty-client ....................................... SUCCESS [  1.006 s][INFO] netty-server ....................................... SUCCESS [  0.501 s][INFO] ------------------------------------------------------------------------[INFO] BUILD SUCCESS[INFO] ------------------------------------------------------------------------[INFO] Total time: 1.603 s[INFO] Finished at: 2017-05-03T15:37:41+08:00[INFO] Final Memory: 16M/177M[INFO] ------------------------------------------------------------------------

5.2 在命令行中进入netty-parent/netty-server目录，运行server

D:\workspace\netty-parent\netty-server>mvn exec:java -Dexec.mainClass="Server"[WARNING][WARNING] Some problems were encountered while building the effective settings[WARNING] expected START_TAG or END_TAG not TEXT (position: TEXT seen ...</localRepository>\ua0\n  <o... @262:5)  @ D:\lyl\00-WORK\java&javaweb\tools\apache-maven-3.3.9\conf\settings.xml, line 262, column 5[WARNING][INFO] Scanning for projects...[INFO][INFO] ------------------------------------------------------------------------[INFO] Building netty-server 0.0.1-SNAPSHOT[INFO] ------------------------------------------------------------------------[INFO][INFO] --- exec-maven-plugin:1.6.0:java (default-cli) @ netty-server ---

5.3 此时Server端已经运行起来了，再打开一个cmd命令窗口，在命令行中进入netty-parent/netty-client目录，运行client

D:\workspace\netty-parent\netty-client>mvn exec:java -Dexec.mainClass="Client" -Dexec.args="localhost 8080"[WARNING][WARNING] Some problems were encountered while building the effective settings[WARNING] expected START_TAG or END_TAG not TEXT (position: TEXT seen ...</localRepository>\ua0\n  <o... @262:5)  @ D:\lyl\00-WORK\java&javaweb\tools\apache-maven-3.3.9\conf\settings.xml, line 262, column 5[WARNING][INFO] Scanning for projects...[INFO][INFO] ------------------------------------------------------------------------[INFO] Building netty-client 0.0.1-SNAPSHOT[INFO] ------------------------------------------------------------------------[INFO][INFO] --- exec-maven-plugin:1.6.0:java (default-cli) @ netty-client ---Client received: Netty rocks!

与此同时，Server端的窗口也接收到了信息
这里写图片描述

到此，第一个netty demo运行完毕.
注意mainClass，我demo里没有限定package名，所以mainClass=”Client”。

项目github地址

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