【Netty4 简单项目实践】八、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();
}
}
});
}
});
}
}