java - netty中如何在断开连接后自动连接到TCP服务器

Question

我有一个场景，我正在使用 netty NIO 建立 TCP 连接，假设服务器出现故障，那么当它再次出现时我如何自动连接到服务器？ 或者有什么方法可以在服务器上附加可用性监听器吗？

Answer 1

您可以有一个 DisconnectionHandler，作为客户端管道上的第一件事，它通过立即尝试重新连接或安排重新连接任务来对 channelInactive 使用react。

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();
  }

}

ReconnectionTask 应该是这样的:

public class ReconnectionTask implements 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.
    }
}

在此处查看 Exponential Backoff library 的示例.