Question

I am writing a server-client application. I have a server that holds several sockets that I have got from the accept() method of ServerSocket. I want to read from these sockets but I don’t necesserally know which socket is ready to be read from. I need some kind of selector that will select one of the sockets that are ready to be read from, so I can read the data it sends.

Thanks.

Answer 1

You have basically two options to make it work:

1. Have dedicated thread per accepted socket. This is because the ‘regular’ socket I/O is blocking. You can not selectively handle multiple sockets using a single thread. And as there is no ‘peeking’ functionality, you will always take a risk of getting blocked when you invoke read. By having a thread per each socket you are interested in reading, blocking reads will not block any other operations (threads).
2. Use NIO. NIO allows for asynchronous I/O operations, and basically exactly what you asked for – a Selector.

If you do decide to go NIO-way, I would recommend checking out MINA and Netty. I’ve found them much easier to work with than plain NIO. Not only will you get a nicer API to work with, but at least MINA had workarounds for some nasty NIO bugs, too.