RXTX 如何从 com 端口读取

Question

Hi i have somthing like this

package compot;

import java.util.Enumeration;
import gnu.io.*;


public class core {

    private static SerialPort p;

    /**
     * @param args
     */
    public static void main(String[] args) 
    {
        Enumeration ports = CommPortIdentifier.getPortIdentifiers();
        System.out.println("start");
        while(ports.hasMoreElements())
        {
            CommPortIdentifier port = (CommPortIdentifier) ports.nextElement();
            System.out.print(port.getName() + " -> " + port.getCurrentOwner() + " -> ");
            switch(port.getPortType())
            {
                case CommPortIdentifier.PORT_PARALLEL:
                    System.out.println("parell");
                break;
                case CommPortIdentifier.PORT_SERIAL:
                    //System.out.println("serial");
                try {
                    p = (SerialPort) port.open("core", 1000);
                    int baudRate = 57600; // 57600bps
                    p.setSerialPortParams(
                            baudRate,
                            SerialPort.DATABITS_8,
                            SerialPort.STOPBITS_1,
                            SerialPort.PARITY_NONE);
                } catch (PortInUseException e) {
                    System.out.println(e.getMessage());
                } catch (UnsupportedCommOperationException e) {
                    System.out.println(e.getMessage());
                }
                break;
            }
        }
        System.out.println("stop");
    }
}

But I dont know how to read from port?? I have read this tutorial but i dont know what "Demo application" they mean??

EDIT

OutputStream outStream = p.getOutputStream();
                    InputStream inStream = p.getInputStream();

                    BufferedReader in = new BufferedReader( new InputStreamReader(inStream));
                    String inputLine;

                    while ((inputLine = in.readLine()) != null) 
                        System.out.println(inputLine);
                    in.close();

I have add this code but i recive

Stable Library ========================================= Native lib Version = RXTX-2.1-7 Java lib Version = RXTX-2.1-7 start /dev/ttyUSB3 -> null -> Underlying input stream returned zero bytes stop

Answer 1

Is this your code? What are you actually trying to do there? :p

In order to read from a SerialPort, you need to declare this port:

CommPortIdentifier portIdentifier = CommPortIdentifier.getPortIdentifier("/dev/tty/USB0"); //on unix based system

Then open a connection on this port:

SerialPort serialPort = (SerialPort) portIdentifier.open("NameOfConnection-whatever", 0);

Next step would be to set the params of this port (if needed):

serialPort.setSerialPortParams(38400, SerialPort.DATABITS_8, SerialPort.STOPBITS_1, SerialPort.PARITY_NONE);

This is my config - your's might differ accordingly:)

Now you're ready to read some data on this port, To get the data: you need to get the serialPorts inputstream and read from that:

InputStream inputStream = serialPort.getInputStream();
while (active) {
        try {
            byte[] buffer = new byte[22];
            while ((buffer[0] = (byte) inputStream.read()) != 'R') {
            }
            int i = 1;
            while (i < 22) {
                if (!active) {
                    break;
                }
                buffer[i++] = (byte) inputStream.read();
            }
            //do with the buffer whatever you want!
        } catch (IOException ex) {
            logger.error(ex.getMessage(), ex);
        }
}

What I'm actually doing here is reading from the inputstream using it's read() method. This will block until data is available or return -1 if end of stream is reached. In this example I wait until I get an 'R' character and then read the next 22 bytes into a buffer. And that's how you read data.

1. Get the serialPorts inputstream
2. use.read() method
3. have that all inside a loop and exit loop when canceled (in my case, the active can be set to false by another method and thus end the reading process.

hope this helps

Answer 2

Try using

if (socketReader.ready()) {
}

so that the socket responds only when there is something to read in the Buffer Stream so the Exception never Occurs.

Answer 3

Something like this in your try block:

OutputStream outStream = p.getOutputStream();
InputStream inStream = p.getInputStream();