Netty4转发服务的实现方案

如果用Netty做转发服务（不需要同步应答），Netty中有一种特殊的模式来满足这个需求。

其原理是在Handler中再启用新的Bootstrap，这个新的Bootstrap和外层的Bootstrap可以共享同一个Channel，

新的Bootstrap为客户端模式，连接到转发目标服务地址，具体实现如下：

import java.net.InetSocketAddress;
 
import io.netty.bootstrap.Bootstrap;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
 
public class Aaa {
    public static void main(String[] params) {
        ServerBootstrap bootstrap = new ServerBootstrap();
        bootstrap.group(new NioEventLoopGroup(), new NioEventLoopGroup())
            .channel(NioServerSocketChannel.class)
            .childHandler(new ChannelInitializer<Channel>() {
                @Override
                protected void initChannel(Channel ch) throws Exception {
                    // TODO Auto-generated method stub
                    ch.pipeline().addLast(new StringDecoder()); 
                    ch.pipeline().addLast(new StringEncoder());
                    ch.pipeline().addLast(new SimpleChannelInboundHandler<String>() {
                        private ChannelHandlerContext innerCtx;
                        ChannelFuture connectFuture;
                        @Override
                        public void channelActive(ChannelHandlerContext ctx)
                                throws Exception {
                            Bootstrap bootstrap = new Bootstrap();
                            bootstrap.channel(NioSocketChannel.class).handler(
                                new SimpleChannelInboundHandler<ByteBuf>() {
                                    //内层建立的连接，从这里接收内层的应答，在这里是服务端的应答
                                    @Override
                                    protected void channelRead0(
                                        ChannelHandlerContext ctx, ByteBuf in)
                                        throws Exception {
                                        innerCtx = ctx;
                                        
                                        byte[] dst = new byte[in.readableBytes()];
                                        in.readBytes(dst);
                                        
                                        System.out.println("Received data" + new String(dst));
                                    }
                                    
                                    @Override
                                    public void channelActive(ChannelHandlerContext ctx) throws Exception {
                                        System.out.println("链接服务"+ctx.channel().toString());
                                    }
                                } );
                            bootstrap.group(ctx.channel().eventLoop());//关键在这里。把外层channel的eventLoop挂接在内层上
                            connectFuture = bootstrap.connect(
//                                new InetSocketAddress("192.168.60.49", 23456));
                                    new InetSocketAddress("localhost", 23456));
                        }
 
                        @Override
                        protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
                            // TODO Auto-generated method stub
                            if (connectFuture.isDone()) {
                                // do something with the data
                                //channel并不共享，共享的是线程EventLoop，所以如果想向内层转发的话
                                //需要持有内层的channel
 
                                if (innerCtx != null && innerCtx.channel().isActive()) {
                                    innerCtx.writeAndFlush(msg);
                                }
                            }
                        }
                    });
                    ChannelFuture future = bootstrap.bind(new InetSocketAddress(8080));
                    future.addListener(new ChannelFutureListener() {
                        @Override
                        public void operationComplete(ChannelFuture channelFuture)
                                throws Exception {
                            if (channelFuture.isSuccess()) {
                                System.out.println("Server bound 8080");
                            } else {
                                System.err.println("Bind attempt failed");
                                channelFuture.cause().printStackTrace();
                            }
                        } 
                    });
                }
            });
    }
}