【超详细解释】从Java NIO到Netty的每一步 (五)

Netty 组件介绍

因为Netty被用于架构或者中间件底层通讯，所以平时我并没有直接基于Netty进行编程过，所以先大概读一下用户手册，发现用户手册Netty对基本概念两三句话概括了之，所以自己先研究了下Netty核心组件的基本概念，之后再去读源码。

从抛弃服务代码讲起

package netty;

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 DiscardServer {
    private int port;

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

    public void run() throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup(); // (1)
        EventLoopGroup workerGroup = new NioEventLoopGroup();// (1)
        try {
            // Netty的服务启用类
            ServerBootstrap b = new ServerBootstrap(); 
            b.group(bossGroup, workerGroup) // (1)
                    // 简单理解为Netty自己写了一个ServerSocketChannel接收连接请求
                    .channel(NioServerSocketChannel.class) 
                    // 可以理解我们给SocketChannel添加handler对其进行处理
                    .childHandler(new ChannelInitializer<SocketChannel>() { 
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new DiscardServerHandler()); //(2)
                        }
                    })
                    //对NioServerSocketChannel进行配置
                    .option(ChannelOption.SO_BACKLOG, 128)  
                    //对SocketChannel进行配置
                    .childOption(ChannelOption.SO_KEEPALIVE, true);

            // 绑定端口开始接收请求
            ChannelFuture f = b.bind(port).sync();
            // 简单理解为关闭服务
            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port = 8080;
        if (args.length > 0) {
            port = Integer.parseInt(args[0]);
        }

        new DiscardServer(port).run();
    }
}      

package netty;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

/**
 * 自定义处理I/O请求
 */
public class DiscardServerHandler extends ChannelInboundHandlerAdapter {//(3)

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        // 丢弃接收到的数据.
        ((ByteBuf) msg).release(); 
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        // 当发生异常时关闭连接.
        cause.printStackTrace();
        ctx.close();
    }

}      

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