如何在netty中斷開連接後自動連接到TCP服務器

Question

我有一個場景，我使用netty NIO建立TCP連接，假設服務器發生故障，當它再次出現時如何自動連接到服務器？ 或者有任何方法可以在服務器上附加可用性監聽器嗎？

Answer 1

您可以讓DisconnectionHandler作爲客戶端管道上的第一件事情，它通過立即嘗試重新連接或調度重新連接任務來對channelInactive做出反應。

例如，

public class DisconnectionHandler extends ChannelInboundHandlerAdapter { 

    @Override 
    public void channelInactive(final ChannelHandlerContext ctx) throws Exception { 

    Channel channel = ctx.channel(); 

    /* If shutdown is on going, ignore */ 
    if (channel.eventLoop().isShuttingDown()) return; 

    ReconnectionTask reconnect = new ReconnectionTask(channel); 
    reconnect.run(); 
    } 

} 

的ReconnectionTask會是這樣的：

public class ReconnectionTask extends Runnable, ChannelFutureListener { 

    Channel previous; 

    public ReconnectionTask(Channel c) { 
     this.previous = c; 
    } 

    @Override 
    public void run() { 
     Bootstrap b = createBootstrap(); 
     b.remoteAddress(previous.remoteAddress()) 
      .connect() 
      .addListener(this); 
    } 

    @Override 
    public void operationComplete(ChannelFuture future) throws Exception { 
     if (!future.isSuccess()) { 
      // Will try to connect again in 100 ms. 
      // Here you should probably use exponential backoff or some sort of randomization to define the retry period. 
      previous.eventLoop() 
        .schedule(this, 100, MILLISECONDS); 
      return; 
     } 
     // Do something else when success if needed. 
    } 
} 

檢查這裏的Exponential Backoff library一個例子。