Managing multiple socket connections in a java server application

Question

In our new project we need to implement a server application. This server gets connection requests of 50,000(+) clients. Problem is these connections have to remain open and have to be managed somewhere. The application should work like a telephone exchange. So it can get requests of connected clients and connect them to other (maybe several) clients only if they are also connected. A proprietary protocol is used. My questions are:

How (and where) to manage the open sockets? Should I put them in a HashMap or something? This sounds curious to me. But I don't have experiences with so many open connections.

Are there any frameworks available which support this connection requirements?

Thank you for your help!

Answer 1

How (and where) to manage the open sockets? Should I put them in a HashMap or something?

Typically each socket will be managed by a thread that will be responsible for reading and writing to the socket. You would also have a master thread that is responsible for receiving all connection requests at a predefined network interface & port (using the ServerSocket API class), which may then hand off the actual processing work to the worker/slave threads. In this case, you ought to be looking at a thread pool for the worker threads, because creating 50k threads will most likely overwhelm your OS and the hardware.

Also, if you are indeed managing 50k concurrent sockets, using NIO API (java.nio.*) over the plain IO API of Java is highly recommended, although I haven't seen too many projects requiring more than 2-5k concurrent connections. There are atleast two known NIO based frameworks in the Java world - Apache MINA and JBoss Netty. I would however recommend reading the well written NIO tutorial, before heading onto use the NIO API or the NIO frameworks.