Netty4.0学习笔记系列之一：Server与Client的通讯

向右看齐 2022-04-11 09:10 145阅读 0赞

本文是学习Netty的第一篇文章，主要对Netty的Server和Client间的通讯机制进行验证。

Server与Client建立连接后，会执行以下的步骤：

1.Client向Server发送消息：Are you ok?

2.Server接收客户端发送的消息，并打印出来。

3.Server端向客户端发送消息：I am ok!

4.Client接收Server端发送的消息，并打印出来，通讯结束。

涉及到的类有4个：

1.HelloServer ：server类，启动Netty server

2.HelloServerInHandler：server的handler，接收客户端消息，并向客户端发送消息

3.HelloClient：client类，建立于Netty server的连接

4.HelloClientIntHandler：client的handler，接收server端的消息，并向服务端发送消息

HelloServer.java

package com.bijian.netty.server;
    
    import io.netty.bootstrap.ServerBootstrap;
    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.NioServerSocketChannel;
    
    public class HelloServer {
        
        public void start(int port) throws Exception {
            
            EventLoopGroup bossGroup = new NioEventLoopGroup();
            EventLoopGroup workerGroup = new NioEventLoopGroup();
            try {
                ServerBootstrap b = new ServerBootstrap();
                b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)
                        .childHandler(new ChannelInitializer<SocketChannel>() {
                            @Override
                            public void initChannel(SocketChannel ch) throws Exception {
                                // 注册handler
                                ch.pipeline().addLast(new HelloServerInHandler());
                            }
                        }).option(ChannelOption.SO_BACKLOG, 128).childOption(ChannelOption.SO_KEEPALIVE, true);
    
                ChannelFuture f = b.bind(port).sync();
    
                f.channel().closeFuture().sync();
            } finally {
                workerGroup.shutdownGracefully();
                bossGroup.shutdownGracefully();
            }
        }
    
        public static void main(String[] args) throws Exception {
            HelloServer server = new HelloServer();
            server.start(8000);
        }
    }

HelloServerInHandler.java

package com.bijian.netty.server;
    
    import io.netty.buffer.ByteBuf;
    import io.netty.channel.ChannelHandlerContext;
    import io.netty.channel.ChannelInboundHandlerAdapter;
    
    import org.apache.commons.logging.Log;
    import org.apache.commons.logging.LogFactory;
    
    // 该handler是InboundHandler类型
    public class HelloServerInHandler extends ChannelInboundHandlerAdapter {
        
        private static Log logger = LogFactory.getLog(HelloServerInHandler.class);
    
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            
            logger.info("HelloServerInHandler.channelRead");
            ByteBuf result = (ByteBuf) msg;
            byte[] result1 = new byte[result.readableBytes()];
            // msg中存储的是ByteBuf类型的数据，把数据读取到byte[]中
            result.readBytes(result1);
            String resultStr = new String(result1);
            // 接收并打印客户端的信息
            System.out.println("Client said:" + resultStr);
            // 释放资源，这行很关键
            result.release();
    
            // 向客户端发送消息
            String response = "I am ok!";
            // 在当前场景下，发送的数据必须转换成ByteBuf数组
            ByteBuf encoded = ctx.alloc().buffer(4 * response.length());
            encoded.writeBytes(response.getBytes());
            ctx.write(encoded);
            ctx.flush();
        }
    
        @Override
        public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
            ctx.flush();
        }
    }

HelloClient.java

package com.bijian.netty.client;
    
    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 HelloClient {
        
        public void connect(String host, int port) throws Exception {
            
            EventLoopGroup workerGroup = new NioEventLoopGroup();
            try {
                Bootstrap b = new Bootstrap();
                b.group(workerGroup).channel(NioSocketChannel.class).option(ChannelOption.SO_KEEPALIVE, true)
                        .handler(new ChannelInitializer<SocketChannel>() {
                            @Override
                            public void initChannel(SocketChannel ch) throws Exception {
                                ch.pipeline().addLast(new HelloClientIntHandler());
                            }
                        });
    
                // Start the client.
                ChannelFuture f = b.connect(host, port).sync();
                
                // Wait until the connection is closed.
                f.channel().closeFuture().sync();
            } finally {
                workerGroup.shutdownGracefully();
            }
        }
    
        public static void main(String[] args) throws Exception {
            HelloClient client = new HelloClient();
            client.connect("127.0.0.1", 8000);
        }
    }

HelloClientIntHandler.java

package com.bijian.netty.client;
    
    import io.netty.buffer.ByteBuf;
    import io.netty.channel.ChannelHandlerContext;
    import io.netty.channel.ChannelInboundHandlerAdapter;
    
    import org.apache.commons.logging.Log;
    import org.apache.commons.logging.LogFactory;
    
    public class HelloClientIntHandler extends ChannelInboundHandlerAdapter {
        
        private static Log logger = LogFactory.getLog(HelloClientIntHandler.class);
    
        // 接收server端的消息，并打印出来
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            
            logger.info("HelloClientIntHandler.channelRead");
            ByteBuf result = (ByteBuf) msg;
            byte[] result1 = new byte[result.readableBytes()];
            result.readBytes(result1);
            System.out.println("Server said:" + new String(result1));
            result.release();
        }
    
        // 连接成功后，向server发送消息
        @Override
        public void channelActive(ChannelHandlerContext ctx) throws Exception {
            
            logger.info("HelloClientIntHandler.channelActive");
            String msg = "Are you ok?";
            ByteBuf encoded = ctx.alloc().buffer(4 * msg.length());
            encoded.writeBytes(msg.getBytes());
            ctx.write(encoded);
            ctx.flush();
        }
    }

通过上面简单的实例可以发现：

1.在没有任何encoder、decoder的情况下，Netty发送接收数据都是按照ByteBuf的形式，其它形式都是不合法的。

2.接收发送数据操作都是通过handler实现的，handler在netty中占据了非常重要的位置。

3.netty的handler是基于事件触发的，例如当client连接server成功后，client中的HelloClientIntHandler的channelActive方法会自动调用。

文章来源：[http://blog.csdn.net/u013252773/article/details/21046697][http_blog.csdn.net_u013252773_article_details_21046697]

[http_blog.csdn.net_u013252773_article_details_21046697]: http://blog.csdn.net/u013252773/article/details/21046697