How to type in commands automatically in cmd window at a high speed in order to test program reliability?

I made a simple chat room application consists of a client.jar and server.jar. After running the .jar file in cmd window, I need to type in some specified command in client part and carriage return to run the application, such as "#connect": connect to the server, "#send XXX": send XXX message to server and broadcast to other connected clients...

Here comes the problems. Actually I want to test how the application works well when there exist concurrency. So I think I need try to let two or more client parts send the command repeatedly and fast. But obviously i cannot achieve manually.

Is there any ways can let the system get the command and send it automatically at high speed? I guess using batch file is suitable for this issue, but I am not sure or how to implement it...