I'm have a bit of trouble understanding what you're on about.
First of all @sissy the USB/RS232 appears as a serial port on the computer. So to find out what is going on at the db9 pin, you open the serial port and you can access the status of the db9 connector. The status passes from the pins of the db9 through the RS232/USB converter through the USB data lines into the computer. If this is not what you're after, then sorry I can't help you.
I can't help you with Java. C#/C/C++/VB.NET/VB6 would be a different story.