Netty Client 重连实现

当咱们用Netty实现一个TCP client时，咱们固然但愿当链接断掉的时候Netty可以自动重连。
Netty Client有两种状况下须要重连：

1. Netty Client启动的时候须要重连
2. 在程序运行中链接断掉须要重连。

对于第一种状况，Netty的做者在stackoverflow上给出了解决方案，
对于第二种状况，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链接成功，不成功的话重试：

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：

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); 

    } 

  } 

}

一样在ChannelHandler监测链接是否断掉，断掉的话也要重连：

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); 

   } 

 }

http://stackoverflow.com/questions/19739054/whats-the-best-way-to-reconnect-after-connection-closed-in-netty参考文档

• 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