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：

Netty Client启动的时候需要重连
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：

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); 
    } 
  } 
}

同样在ChannelHandler监测连接是否断掉，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); 
   } 
 }

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