How can I emulate non-blocking i/o in Java using threads

I'm writing a simple application involving a server and many clients at a time. I have to use DataGramSocket. The application is simple exchange of messages through console like in chatting.

However, both operations in.readLine() and ds.receive() are blocking and putting them in separate threads didn't help as blocking i/o will block the thread too. How can I do that without nio?

If you have threads which are dedicated only to sending or receiving data over network, then thread blocking won't be a problem, as only that dedicated thread will be blocked.

Then, let's consider impact of this solution on number of threads in your application:

• If you have only few clients per server, then having 2 I/O threads per client isn't a problem.
• If you have lots of clients per server, then you should accept the fact that some of their requests will be processed not immediately but only then worker thread becomes available. You can try to spawn as much I/O threads as there are clients, but there are limitations on the number of threads single JVM instance can have. Exact numbers depend on the size of heap available to your JVM and whether your architecture is 32bit or 64bit, see here.

If you interested in general task of handling lots of clients, here is the classic web paper on this question.