I want to make a Java program that allow me this discover my nearby computers who is running the same problem. Which is similar like the iTunes, can discover nearby computer who enable sharing in the iTunes. How can I implement it using open source library? Also, cross platform is very important. Any ideas on that? Thank you.
I think you definitely should take a look at UPnP. Considering the cross-platformness of such a solution, and its implementation using Java, you can consider
Finally, considering existing implementation of Bonjour using Java, this reply to a stackoverflow question sums it up.