How to find an available port?

Question

I want to start a server which listen to a port. I can specify port explicitly and it works. But I would like to find a port in an automatic way. In this respect I have two questions.

1. In which range of port numbers should I search for? (I used ports 12345, 12346, and 12347 and it was fine).

2. How can I find out if a given port is not occupied by another software?

Answer 1

If you pass 0 as the port number to the constructor of ServerSocket, It will allocate a port for you.