在ubuntu上使用Java进行串行端口识别

Question

I'm trying to connect a serial application on ubuntu with Java
After searching and reading resources,I add comm.jar and RXTXcomm.jar in the library.
I use the following code to identify the comports. In my system there are three ports but it is showing false in ports.hasMoreElements() method.
Kindly look into the code and help me.

String wantedPortName = "/dev/ttya";
///dev/ttyS0 و /dev/ttyS1 نیز تست شد
Enumeration portIdentifiers = CommPortIdentifier.getPortIdentifiers();
CommPortIdentifier portId = null;  // will be set if port found
while (portIdentifiers.hasMoreElements())
{
    CommPortIdentifier pid = (CommPortIdentifier) portIdentifiers.nextElement();
    if(pid.getPortType() == CommPortIdentifier.PORT_SERIAL &&
      pid.getName().equals(wantedPortName)) 
  {
    portId = pid;
    break;
  }
}
if(portId == null)
{
     System.err.println("Could not find serial port " + wantedPortName);
     System.exit(1);
}    

Answer 1

In my case, I'm using Ubuntu, and my notebook does not have any serial or paralel ports.

So, you have to simulate this kind of port:

apt-get install socat

Run it:

socat -d -d pty,raw,echo=0, pty,raw,echo=0

According to output, pay attention to "devices" created:

2014/02/05 01:04:32 socat[7411] N PTY is /dev/pts/2
2014/02/05 01:04:32 socat[7411] N PTY is /dev/pts/3
2014/02/05 01:04:32 socat[7411] N starting data transfer loop with FDs [3,3] and [5,5]

Stop socat [CTRL]+[C] and symlink it to a location that RXTX will recognise as a device, due to "tty" prefix:

sudo ln -s /dev/pts/2 /dev/ttyUSB02
sudo ln -s /dev/pts/3 /dev/ttyUSB03

Now, run socat again

socat -d -d pty,raw,echo=0 pty,raw,echo=0

Now, using following code, you will see 2 virtual ports:

        Enumeration portList = CommPortIdentifier.getPortIdentifiers();//this line was false
        System.out.println(portList.hasMoreElements());

        while(portList.hasMoreElements()){
            System.out.println("Has more elements");
             CommPortIdentifier portId = (CommPortIdentifier) portList.nextElement();
               if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {
                    System.out.println(portId.getName());
               }
               else{
                     System.out.println(portId.getName());
               }
        }

system.out:

true
Has more elements
/dev/ttyUSB03
Has more elements
/dev/ttyUSB02

Answer 2

It looks like you are filtering out the port you want. A /dev/tty is a special character device... not a serial port so

if(pid.getPortType() == CommPortIdentifier.PORT_SERIAL &&
  pid.getName().equals(wantedPortName)) 

should never match your string.

To prove this, try iterating over your available ports. I don't know if a tty can can be detected by RXTX but play with it and let us know.

Ref: http://rxtx.qbang.org/wiki/index.php/Discovering_available_comm_ports

EDIT: So you don't have any serial devices to test with? All I sat is make sure you have everything installed properly, including the properties file as described in this file.

http://rxtx.qbang.org/pub/rxtx/rxtx-2.0-7pre2/INSTALL

Once done, install a null modem emulator or find a serial device to test with.