Netty关于Channel的使用的官方解释

package io.netty.example.discard;

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;

/**
 * Discards any incoming data.
 */
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();
        try {
            ServerBootstrap b = new ServerBootstrap(); // (2)
            b.group(bossGroup, workerGroup)
             .channel(NioServerSocketChannel.class) // (3)
             .childHandler(new ChannelInitializer<SocketChannel>() { // (4)
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {
                     ch.pipeline().addLast(new DiscardServerHandler());
                 }
             })
             .option(ChannelOption.SO_BACKLOG, 128)          // (5)
             .childOption(ChannelOption.SO_KEEPALIVE, true); // (6)

            // Bind and start to accept incoming connections.
            ChannelFuture f = b.bind(port).sync(); // (7)

            // Wait until the server socket is closed.
            // In this example, this does not happen, but you can do that to gracefully
            // shut down your server.
            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }

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

• NioEventLoopGroup is a multithreaded event loop that handles I/O operation. Netty provides various EventLoopGroup implementations for different kind of transports. We are implementing a server-side application in this example, and therefore two NioEventLoopGroup will be used. The first one, often called 'boss', accepts an incoming connection. The second one, often called 'worker', handles the traffic of the accepted connection once the boss accepts the connection and registers the accepted connection to the worker. How many Threads are used and how they are mapped to the created Channels depends on the EventLoopGroupimplementation and may be even configurable via a constructor.

• ServerBootstrap is a helper class that sets up a server. You can set up the server using a Channel directly. However, please note that this is a tedious process, and you do not need to do that in most cases.

• Here, we specify to use the NioServerSocketChannel class which is used to instantiate a new Channel to accept incoming connections.

• The handler specified here will always be evaluated by a newly accepted Channel. The ChannelInitializer is a special handler that is purposed to help a user configure a new Channel. It is most likely that you want to configure the ChannelPipeline of the new Channel by adding some handlers such as DiscardServerHandlerto implement your network application. As the application gets complicated, it is likely that you will add more handlers to the pipeline and extract this anonymous class into a top level class eventually.

• You can also set the parameters which are specific to the Channel implementation. We are writing a TCP/IP server, so we are allowed to set the socket options such as tcpNoDelay and keepAlive. Please refer to the apidocs of ChannelOption and the specific ChannelConfig implementations to get an overview about the supported ChannelOptions.

• Did you notice option() and childOption()? option() is for the NioServerSocketChannel that accepts incoming connections. childOption() is for the Channels accepted by the parent ServerChannel, which is NioServerSocketChannel in this case.

• We are ready to go now. What's left is to bind to the port and to start the server. Here, we bind to the port 8080 of all NICs (network interface cards) in the machine. You can now call the bind() method as many times as you want (with different bind addresses.

这段程序可以用Telnet去测试