How to send Udp packet 2 or 3 times after failed received packet in java?

Question

I have send Udp packet to the Server. If the server is OK then I can receive the response packet nicely but when the server is down then I did not get any response packet. Anybody can help me that how can I send my packet to server multiple time when fail to receive the response packet. Moreover, want to keep alive the connection with server. Thanks in advance.

Answer 1

Well,

1. After you've sent the packet, you wait for the ACK (response) package from the server. You could use the DatagramSocket.setSoTimeout() to an appropriate time, if you get the Timeout Exception increment a counter, if that counter is less than 2/3 send the packet again and repeat these steps. If the counter is bigger than 2/3 the server is down, just quit.

   According to Java documentation, receive will block until a package is received or a timeout has expired.

2. To keep the connection alive you need to implement a ping-pong. In another thread of your program, you send a Keep-Alive packet (any small packet will do) and wait for a response. I suggest using a different port number for this purpose so that these packets won't mess up with the normal data packets. These packets can be send every 2 seconds o 2 minutes depends on your particular needs. When the thread receives the ACK packet it will update a private time variable with the current time, for example:

   lastTimeSeen = System.currentTimeMillis();

   put a method in your thread class to access the value of that variable.