Reading from COM port in Java, Error 0x5 at ..\rxtx\src\termios.c(892)

Question

I'm writing a small app in Java to read from COM port, and since we use 64 bit systems I had to use RXTX. The problem is when I try to run my app I get the following error:

"Error 0x5 at ..\rxtx\src\termios.c(892):Access Denied"

Tried my code and also the code from RXTX site, anyone had any experience with this before?

---

Here is my code:

import gnu.io.CommPort;
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import gnu.io.SerialPortEvent;
import gnu.io.SerialPortEventListener;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

/**
 * This version of the TwoWaySerialComm example makes use of the 
 * SerialPortEventListener to avoid polling.
 *
 */
public class TwoWaySerialComm
{
    public TwoWaySerialComm()
    {
        super();
    }

    void connect ( String portName ) throws Exception
    {
        CommPortIdentifier portIdentifier = CommPortIdentifier.getPortIdentifier(portName);
        if ( portIdentifier.isCurrentlyOwned() )
        {
            System.out.println("Error: Port is currently in use");
        }
        else
        {
            CommPort commPort = portIdentifier.open(this.getClass().getName(),2000);

            if ( commPort instanceof SerialPort )
            {
                SerialPort serialPort = (SerialPort) commPort;
                serialPort.setSerialPortParams(9600,SerialPort.DATABITS_8,SerialPort.STOPBITS_1,SerialPort.PARITY_NONE);

                InputStream in = serialPort.getInputStream();
//                OutputStream out = serialPort.getOutputStream();
//                               
//                (new Thread(new SerialWriter(out))).start();

                serialPort.addEventListener(new SerialReader(in));
                serialPort.notifyOnDataAvailable(true);

            }
            else
            {
                System.out.println("Not a serial port...");
            }
        }     
    }

    public static class SerialReader implements SerialPortEventListener 
    {
        private InputStream in;
        private byte[] buffer = new byte[1024];

        public SerialReader ( InputStream in )
        {
            this.in = in;
        }

        public void serialEvent(SerialPortEvent arg0) {
            int data;

            try
            {
                int len = 0;
                while ( ( data = in.read()) > -1 )
                {
                    if ( data == '\n' ) {
                        break;
                    }
                    buffer[len++] = (byte) data;
                }
                System.out.print("Result="+new String(buffer,0,len));
            }
            catch ( IOException e )
            {
                e.printStackTrace();
                System.exit(-1);
            }             
        }

    }

    public static void main ( String[] args )
    {
        try
        {
            (new TwoWaySerialComm()).connect("COM1");
        }
        catch ( Exception e )
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

Answer 1

I ran into this problem because the port was actually in use. A previous instance of javaw.exe appeared in the Windows task manager, it hogged the port.

The reason why java processes did hang in CommPortIdentifier was a hardware issue: When plugging the USB-2-serial converter that I happened to use into a USB2 port, all worked fine. When plugged into a USB-3 port, CommPortIdentifier code would hang, and then subsequent instances of Java received the termios.c: Access Denied error.