Why my usb to serial port is not recognized in Ubuntu?

Question

I have to continue the development of a specific java embedded project which talks to some serial external devices.

Previous development was done using Windows and now I try to run it using Ubuntu. I have some port issue when using this code:

    String comport = Gateway.config.getHardwareRevision() <= 1 ? "com0" : "com1";

    String ports = System.getProperty("microedition.commports");
    log.log("---available PORTS: " + ports);

    serial = (CommConnection) Connector .open("comm:" + comport + ";blocking=on;baudrate=" + BAUD_RATES[baudrate]
                    + ";autocts=off;autorts=off");
    inStream = serial.openInputStream();

    outStream = serial.openOutputStream();

Basically I connect my usb to serial cable, noticed that Ubuntu is assigning to it port /dev/ttyUSB0 so I change code to:

    `String comport = Gateway.config.getHardwareRevision() <= 1 ? "/dev/ttyUSB0" : "com1";`

because hw revision is <=1 so it should load this port. Unfortunately after many tries I still receive:

Could not find serial port /dev/ttyUSB0
java.io.IOException: gnu.io.NoSuchPortException
    at javax.microedition.io.SerialConnection.open(SerialConnection.java:57)
    at javax.microedition.io.SerialConnection.<init>(SerialConnection.java:19)
    at javax.microedition.io.Connector.open(Connector.java:43)
    at javax.microedition.io.Connector.open(Connector.java:13)

I read something that I have to use RXTX if developing with Linux but I can't believe that I should rewrite java code just because I change my dev environment.

Do you have any ideas to make this work without refactoring?