Netty Client 重连实现

当我们用Netty实现一个TCP client时，我们当然希望当连接断掉的时候Netty能够自动重连。
Netty Client有两种情况下需要重连：

1. Netty Client启动的时候需要重连
2. 在程序运行中连接断掉需要重连。

对于第一种情况，Netty的作者在stackoverflow上给出了解决方案，
对于第二种情况，Netty的例子uptime中实现了一种解决方案。

而Thomas在他的文章中提供了这两种方式的实现的例子。

实现ChannelFutureListener 用来启动时监测是否连接成功，不成功的话重试：

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public class Client   {     private EventLoopGroup loop = new NioEventLoopGroup();     public static void main( String[] args )     {       new Client().run();     }     public Bootstrap createBootstrap(Bootstrap bootstrap, EventLoopGroup eventLoop) {        if (bootstrap != null) {         final MyInboundHandler handler = new MyInboundHandler(this);         bootstrap.group(eventLoop);         bootstrap.channel(NioSocketChannel.class);         bootstrap.option(ChannelOption.SO_KEEPALIVE, true);         bootstrap.handler(new ChannelInitializer<SocketChannel>() {           @Override           protected void initChannel(SocketChannel socketChannel) throws Exception {             socketChannel.pipeline().addLast(handler);           }         });         bootstrap.remoteAddress("localhost", 8888);        bootstrap.connect().addListener(new ConnectionListener(this));      }       return bootstrap;     }     public void run() {       createBootstrap(new Bootstrap(), loop);    }   }

ConnectionListener 负责重连：

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public class ConnectionListener implements ChannelFutureListener {    private Client client;    public ConnectionListener(Client client) {      this.client = client;    }    @Override    public void operationComplete(ChannelFuture channelFuture) throws Exception {       if (!channelFuture.isSuccess()) {        System.out.println("Reconnect");        final EventLoop loop = channelFuture.channel().eventLoop();        loop.schedule(new Runnable() {          @Override          public void run() {            client.createBootstrap(new Bootstrap(), loop);          }        }, 1L, TimeUnit.SECONDS);      }    }  }

同样在ChannelHandler监测连接是否断掉，断掉的话也要重连：

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public class MyInboundHandler extends SimpleChannelInboundHandler {     private Client client;     public MyInboundHandler(Client client) {       this.client = client;     }     @Override     public void channelInactive(ChannelHandlerContext ctx) throws Exception {        final EventLoop eventLoop = ctx.channel().eventLoop();       eventLoop.schedule(new Runnable() {         @Override         public void run() {           client.createBootstrap(new Bootstrap(), eventLoop);         }       }, 1L, TimeUnit.SECONDS);       super.channelInactive(ctx);     }   }

参考文档

• http://stackoverflow.com/questions/19739054/whats-the-best-way-to-reconnect-after-connection-closed-in-netty
• https://github.com/netty/netty/blob/master/example/src/main/java/io/netty/example/uptime/UptimeClientHandler.java
• http://tterm.blogspot.jp/2014/03/netty-tcp-client-with-reconnect-handling.html
• ctx.close vs ctx.channel().close
• ctx.write vs ctx.channel().write