Listening for TCP and UDP requests on the same port

Question

I am writing a Client/Server set of programs

Depending on the operation requested by the client, I use make TCP or UDP request.

Implementing the client side is

Answer 1

AFAIK, you should be able to listen for both TCP connections and UDP messages on the same port. It would help if you posted your UDP code, and the exception + stacktrace that you are seeing.

Answer 2

You can't use DatagramSocket.receive() in non-blocking mode. You have to use the read() or receive() methods of your DatagramChannel directly.

In fact as you are using non-blocking mode and a Selector, it is quite impossible to see why you're also using a UDPThread at all. Just call udpserver.receive() instead of starting the thread.

Answer 3

It should work. One of the problems with this code, it seems, is that the ByteBuffer size is set to 0, meaning that the datagram is discarded (as it mentions in the comments). If you need to receive any information over UDP and you are on a reliable network, you can set the size quite big and receive big datagrams made up of multiple packets. Otherwise, on an unreliable network, set this to the MTU size. Make sure you flip() the ByteBuffer after receiving anything in it.

Also, creating new threads for each request is a bad idea, create a 'session' thread for each different IP you receive in a HashMap or something, and then do a guarded block on the session object. Wake up the thread sleeping on that object when you receive a message after passing in new information. The selector code you have is designed to avoid the creation of threads in this way.

Edit: based on the above code, you're create a datagram channel and then using the socket to receive datagrams directly? That's doesn't make sense. Use the channel methods only after binding the channel. Also, don't do this in a separate thread. Your code isn't thread-safe and will bust itself up. Hand the received information off to the separate 'session' thread as mentioned earlier. The selector is designed to tell you what channels can be read from without blocking (although blocking is disabled anyway, so it will tell you what channels have data to be read from).