comm.jar通讯串口Java

Question

I am facing problem with using comm.jar.

Problem is I connected the devices and I started the application in pooling using this code

 public static void main(String[] args) {
        Enumeration portList;
        CommPortIdentifier portId = null;
        portList = CommPortIdentifier.getPortIdentifiers();
        while (portList.hasMoreElements()) {
            portId = (CommPortIdentifier) portList.nextElement();
            System.out.println("port::" + portId.getName());

        }
        while (true) {
            try {
                Thread.sleep(2000);
            } catch (InterruptedException ex) {
                Logger.getLogger(JavaComPortFinding.class.getName()).log(Level.SEVERE, null, ex);
            }
            main(args);
        }
    }

output :

port::COM1
port::COM10

After one polling , I have ejected the device. I still get the response as

port::COM1
port::COM10

can anyone help me out / suggest to get dynamic response in polling.

Answer 1

You could try something like that since the CommPortIdentifier should be recreated every time.

class TestProgram
{
    public static void main(String[] args)
    {
        while(true)
        {
            try
            {
                Thread.sleep(2000);
            }
            catch(InterruptedException ex)
            {
                Logger.getLogger(TestProgram.class.getName()).log(Level.SEVERE, null, ex);
            }

            scanPorts();
        }
    }

    private static void scanPorts()
    {
        Enumeration portList;
        CommPortIdentifier portId = null;
        portList = CommPortIdentifier.getPortIdentifiers();

        while (portList.hasMoreElements())
        {
            portId = (CommPortIdentifier) portList.nextElement();
            System.out.println("port::" + portId.getName());

        }
    }
}

EDIT :

I've just tested the program on Windows XP SP3 with my BlackBerry on usb. When I start the program I see the normal COM1 and two COM ports for the BlackBerry. Once I disconnect the BlackBerry, the ports stay in the device manager. If I remove them manually, they dissapear in the program (without restart).

Answer 2

https://community.oracle.com/thread/2063873?start=0&tstart=0

I found the above resource extremely valuable while finding solution for a similar issue.

The main problem here is that static block in CommPortIdentifier gets loaded only once and caches the ports information in field variable portList . When you call the getPortIdentifiers() method, it will return the ports from portList which were detected during the initial load.

The workaround this would be to reload the static block in CommPortIdentifier class and then call getPortIdentifiers() , which will reload the drivers and give you an updated list of COM ports (this was done using Java Reflection API in the link referenced).

Good Luck!