Programatically monitor serial port

On a device with a Windows Embedded POS Ready 7 OS, there is a software, called Mistral (which cannot be modified), that writes some data to a RS-232 serial port, data which is transmitted to another device. Each time data is sent through that port, I need to change the Activity of an Android application. I was thinking to write a piece of software (Java or C#) which detects that the serial port was written (and what was written if possible) and call the mobile application's endpoint every time this happens. I know there are some Windows tools for port monitoring, but I don't know one with a library.

Is it even possible to write to a port and at the same time read from the same port what was just written on that port from two different processes?

Another solution would be to add an extra adapter (like this one: return the signal to another port and read from that port. Or redirect that signal to the mobile application using an USB adapter.

But I would like to know if doing it without extra wires is possible, using Java or C#, for example.