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  • I have been trying to implement a RTU slave application, I used the ListenerTest as a start with the necessary modifications to make it create a RTU slave instead of the TCP slave. However when I try to run it I get a NullPointerException at the SteamTransporter.

    
    run:
    Stable Library
    =========================================
    Native lib Version = RXTX-2.1-7
    Java lib Version   = RXTX-2.1-7
    com.serotonin.modbus4j.exception.ModbusInitException: java.lang.NullPointerException
            at com.serotonin.modbus4j.serial.SerialSlave.start(SerialSlave.java:51)
            at com.serotonin.modbus4j.serial.rtu.RtuSlave.start(RtuSlave.java:40)
            at kiwi.main$1.run(main.java:46)
            at java.lang.Thread.run(Thread.java:662)
    Caused by: java.lang.NullPointerException
            at com.serotonin.messaging.StreamTransport.start(StreamTransport.java:32)
            at com.serotonin.modbus4j.serial.SerialSlave.start(SerialSlave.java:48)
            ... 3 more
    
    

    I looked through the examples but couldn't find any that were very relevant except the listener one. Google didn't really turn up anything useful either. When I looked closer at the code I figured it might be something up with the name being passed to StreamTransport and fetched the thread and got it's name and passed that as a variable instead. That didn't make any difference though.

    Thanks in advance, hope I didn't miss anything painfully obvious :)


  • There is a line in SerialSlave that should be removed.

            try {
                serialPort = SerialUtils.openSerialPort(serialParameters);
                transport = new StreamTransport(serialPort.getInputStream(), serialPort.getOutputStream());
                transport.start("Modbus4J SerialSlave");  // &lt&lt&lt REMOVE THIS LINE
            }
    
    

    The start method should be (and is) called in subclasses. I'm pretty sure this will fix the problem, but i don't have any equipment available to test on. Please let me know if it helps.


  • I've just come across this error from 2011 and I only downloaded the code a few days ago.

    Why was this error still present in the code?

    Anyway, the fix sorted the issue and I now have a working RTU slave.


  • I looked through the examples but couldn't find any that were very relevant except the listener one. Google didn't really turn up anything useful either. When I looked closer at the code I figured it might be something up with the name being passed to StreamTransport and fetched the thread and got it's name and passed that as a variable instead. That didn't make any difference though.


  • The line is not in the CVS code. Perhaps it still is in the src jar file. Try using the repo source instead.