Mismatched RXTX Versions

Question

I found a code to communicate in Java via Serial Port to an Arduino and wanted to try and get it working in order to expand on it for a project idea, but I keep getting this error

Stable Library
=========================================
Native lib Version = RXTX-2.2-20081207 Cloudhopper Build rxtx.cloudhopper.net
Java lib Version   = RXTX-2.1-7
WARNING:  RXTX Version mismatch
Jar version = RXTX-2.1-7
native lib Version = RXTX-2.2-20081207 Cloudhopper Build rxtx.cloudhopper.net
Could not find COM port.
Started

I think that it means there is jar mismatch for the RXTX library, but the link to the build in the native lib is a website is no longer there. I'm not exactly sure how to fix the problem. My code is below if you believe that is the issue. Any help would be appreciated.

import java.io.OutputStream;
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import gnu.io.SerialPortEvent;
import gnu.io.SerialPortEventListener;
import java.io.InputStream;
import java.util.Enumeration;

public class AraInterface {
SerialPort serialPort;
        /** The port we're normally going to use. */
        private static final String PORT_NAMES[] = { 
                        "/dev/tty.usbserial-A9007UX1", // Mac OS X
                        "/dev/ttyUSB0", // Linux
                        "COM35", // Windows //shin: ardu com port here
                        };
        private InputStream input;
        private OutputStream output;
        private static final int TIME_OUT = 2000;
        private static final int DATA_RATE = 9600;

        public void initialize() {
                CommPortIdentifier portId = null;
                Enumeration portEnum = CommPortIdentifier.getPortIdentifiers();

                while (portEnum.hasMoreElements()) {
                        CommPortIdentifier currPortId = (CommPortIdentifier) portEnum.nextElement();
                        for (String portName : PORT_NAMES) {
                                if (currPortId.getName().equals(portName)) { 
                                        portId = currPortId;
                                        break;
                                }
                        }
                }

                if (portId == null) {
                        System.out.println("Could not find COM port.");
                        return;
                }

                try {
                        serialPort = (SerialPort) portId.open(this.getClass().getName(),
                                        TIME_OUT);

                        serialPort.setSerialPortParams(DATA_RATE,
                                        SerialPort.DATABITS_8,
                                        SerialPort.STOPBITS_1,
                                        SerialPort.PARITY_NONE);

                        input = serialPort.getInputStream();
                        output = serialPort.getOutputStream();

                        serialPort.addEventListener((SerialPortEventListener) this);
                        serialPort.notifyOnDataAvailable(true); 
                } catch (Exception e) {
                        System.err.println(e.toString());
                }
        }

        public synchronized void close() {
                if (serialPort != null) {
                        serialPort.removeEventListener();
                        serialPort.close();
                }
        }

        public synchronized void serialEvent(SerialPortEvent oEvent) {
                if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE) {
                        try {
                                int available = input.available();
                                byte chunk[] = new byte[available];
                                input.read(chunk, 0, available);

                                String temp = new String (chunk);
                                String ref = "Hel";
                                if(temp.compareTo(ref)==0){
                                System.out.println("Hello World request received");
                                }
                                else{
                                System.out.println("lala" + temp);
                                }

                        } catch (Exception e) {
                                System.err.println(e.toString());
                        }
                }

        }

        public static void main(String[] args) throws Exception {
                AraInterface main = new AraInterface();
                main.initialize();
                System.out.println("Started");
        }
}

Answer 1

1. Check if you have installed the library. If not, in case of Ubuntu, sudo apt-get install librxtx-java
2. If already installed, go to the path of the installation --- in my case /usr/share/java/RXTXcomm.jar
3. If you are using Ubuntu or any Linux distro, remove any downloaded rxtx library from Eclipse build path, and add the path of the installed rxtx library in step 2. You can also copy it into your project.
4. Check your java library property (System.getProperty("java.library.path")) to know the folder.
5. Copy the librxtxSerial.so to the Java library path - in my case sudo cp -r /usr/lib/jni/librxtxSerial.so /usr/lib/x86_64-linux-gnu

After that try your code again.