reading serial port in java

Question

Hi, i'm begginer in java,i'm reading data from device throgh serial port,i'm getting data for every one minute but first reading is coming half,after that data is coming corectly

output i'm getting is:6050.003120815340006050.003120815350006050.0

correct output should be like this:03120815340006050.003120815350006050.0

my code is:

import java.io.; import java.util.; //import gnu.io.; import javax.comm.;

public class SimpleRead implements Runnable, SerialPortEventListener { static CommPortIdentifier portId; static Enumeration portList;

InputStream inputStream;
SerialPort serialPort;
Thread readThread;
byte[] readBuffer;

public static void main(String[] args) {
 portList = CommPortIdentifier.getPortIdentifiers();
 System.out.println("portList... " + portList);
 while (portList.hasMoreElements()) {
  portId = (CommPortIdentifier) portList.nextElement();
  if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {
   System.out.println("port identified is Serial.. "
     + portId.getPortType());
   if (portId.getName().equals("COM2")) {
    System.out.println("port identified is COM2.. "
      + portId.getName());
    // if (portId.getName().equals("/dev/term/a")) {
    SimpleRead reader = new SimpleRead();
   } else {
    System.out.println("unable to open port");
   }
  }
 }
}

public SimpleRead() {
 try {
  System.out.println("In SimpleRead() contructor");
  serialPort = (SerialPort) portId.open("SimpleReadApp1111",500);
  System.out.println(" Serial Port.. " + serialPort);
 } catch (PortInUseException e) {
  System.out.println("Port in use Exception");
 }
 try {
  inputStream = serialPort.getInputStream();
  System.out.println(" Input Stream... " + inputStream);
 } catch (IOException e) {
  System.out.println("IO Exception");
 }
 try {
  serialPort.addEventListener(this);

 } catch (TooManyListenersException e) {
  System.out.println("Tooo many Listener exception");
 }
 serialPort.notifyOnDataAvailable(true);
 try {

  serialPort.setSerialPortParams(9600, SerialPort.DATABITS_8,
    SerialPort.STOPBITS_1, SerialPort.PARITY_NONE);

  // no handshaking or other flow control
  serialPort.setFlowControlMode(SerialPort.FLOWCONTROL_NONE);

  // timer on any read of the serial port
  serialPort.enableReceiveTimeout(500);

  System.out.println("................");

 } catch (UnsupportedCommOperationException e) {
  System.out.println("UnSupported comm operation");
 }
 readThread = new Thread(this);
 readThread.start();
}

public void run() {
 try {
  System.out.println("In run() function ");
  Thread.sleep(500);
  // System.out.println();
 } catch (InterruptedException e) {
  System.out.println("Interrupted Exception in run() method");
 }
}

public void serialEvent(SerialPortEvent event) {

 // System.out.println("In Serial Event function().. " + event +
 // event.getEventType());
 switch (event.getEventType()) {
 /*
  * case SerialPortEvent.BI: case SerialPortEvent.OE: case
  * SerialPortEvent.FE: case SerialPortEvent.PE: case SerialPortEvent.CD:
  * case SerialPortEvent.CTS: case SerialPortEvent.DSR: case
  * SerialPortEvent.RI: case SerialPortEvent.OUTPUT_BUFFER_EMPTY: break;
  */
 case SerialPortEvent.DATA_AVAILABLE:
  readBuffer = new byte[8];

  try {

   while (inputStream.available()>0) {

    int numBytes = inputStream.read(readBuffer);
   //  System.out.println("Number of bytes read " + numBytes);
   }

   System.out.print(new String(readBuffer));

  } catch (IOException e) {
   System.out.println("IO Exception in SerialEvent()");
  }
  break;
 }
 // System.out.println();
/* String one = new String(readBuffer);
 char two = one.charAt(0);
 System.out.println("Character at three: " + two);*/
}

}

Answer 1

This looks as if you were reading the rest of some message which was sent before you started.

Try to read as much data as possible as you start the program to clear any hardware buffers. After that, start your processing.

Answer 2

Try flushing the input buffer of the port before doing your read. Otherwise, if the sending end has sent data during your program's startup (or closely before, that might be up to the operating system), you will get old buffered data.

Also, if possible, consider adding message framing to the protocol, so you can detect when you have read something that is not, in fact, a complete message, and discard it. This is often very helpful with these kinds of issues.

Answer 3

Use the following:

while (inputStream.available()>0) {
  int numBytes = inputStream.read(readBuffer);
  System.out.print(new String(readBuffer));
}

You are printing the result out of the while loop. However the code inside the loop may run more than once, so chunk of data will be lost.