Java Netty 学习笔记（二）使用Netty编程

电玩女神 2022-06-15 02:53 199阅读 0赞

熟悉了使用java nio编程的套路，实际上就跟底层socket的没啥区别。  
下面学习如何使用Netty编写简单的Time Server。  
代码：[https://github.com/NearXdu/NettyLearn][https_github.com_NearXdu_NettyLearn]

public class TimeServer {
        
        public void bind(int port) throws Exception{
            //配置服务端的NIO线程组
            //
            EventLoopGroup bossGroup = new NioEventLoopGroup();
            EventLoopGroup workerGroup = new NioEventLoopGroup();
            try{
                ServerBootstrap b = new ServerBootstrap();
                b.group(bossGroup,workerGroup)
                        .channel(NioServerSocketChannel.class)
                        .option(ChannelOption.SO_BACKLOG,1024)
                        .childHandler(new ChildChannelHandler());
                //绑定端口，同步等待成功
                ChannelFuture f = b.bind(port).sync();
                //等待服务端监听端口关闭
                f.channel().closeFuture().sync();
            }finally {
                //释放线程池资源
                bossGroup.shutdownGracefully();
                workerGroup.shutdownGracefully();
            }
        }
    
        private class ChildChannelHandler extends ChannelInitializer<SocketChannel> {
        
    
            @Override
            protected void initChannel(SocketChannel ch) throws Exception {
                ch.pipeline().addLast(new TimeServerHandler());
    
            }
        }
    
        public static void main(String[] args) throws Exception{
            int port =1025;
            if(args!=null && args.length>0){
                try{
                    port =Integer.valueOf(args[0]);
                }catch (NumberFormatException e){
    
                }
            }
            new TimeServer().bind(port);
        }
    }

1.`NioEventLoopGroup`:Reactor线程组，用于处理网络事件。  
2.`ServerBootstrap`:Netty用于启动NIO服务端的辅助启动类。  
3.`ServerBootstrap`的`group`方法设置监听套接字`NioServerSocketChannel`  
设置BACKLOG，设置IO事件的处理类`ChildChannelHandler`  
4.`ServerBootstrap`的`bind`方法绑定监听端口

在Handler类中，有些区别就是netty4和netty5的API会有些出入，在书中继承ChannelHandlerAdapter，我用的是Netty4,因此需要稍微改写：

public class TimeServerHandler extends ChannelInboundHandlerAdapter {
        
    
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg)
                throws Exception {
            ByteBuf buf = (ByteBuf) msg;//read buff
            byte[] req = new byte[buf.readableBytes()];//通过readble获取到大小
            buf.readBytes(req);//readByte将数据塞入req中
        //业务
            String body = new String(req, "UTF-8");
            System.out.println("The time server receive order : " + body);
            String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body.trim()) ? new java.util.Date(
                    System.currentTimeMillis()).toString() : "BAD ORDER";
        //构造响应
            ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
        //发送
            ctx.write(resp);
        }
    }

这个方法就有点类似muduo中onMessage，或者libevent中onRead回调了，数据通过参数传递，并使用封装的缓存接收，最后构造业务响应。

参考：  
1) netty权威指南  
2) [http://stackoverflow.com/questions/24844042/extends-channelhandleradapter-but-does-not-override-or-implement-a-method-from][http_stackoverflow.com_questions_24844042_extends-channelhandleradapter-but-does-not-override-or-implement-a-method-from]

[https_github.com_NearXdu_NettyLearn]: https://github.com/NearXdu/NettyLearn
[http_stackoverflow.com_questions_24844042_extends-channelhandleradapter-but-does-not-override-or-implement-a-method-from]: http://stackoverflow.com/questions/24844042/extends-channelhandleradapter-but-does-not-override-or-implement-a-method-from