Thread: Reading wrong value from serial port

I have to read the 12-digit tag number from an RFID reader and print it to console. When I use this program to read the tag I get some weird spacing in between.

E.g. My tag number is 4400E6EF1A57. When I keep scanning this tag, the console window shows the following:

4400E6EF1
A57

4400E
6EF1A57


4400E6EF1A57


4400E6EF1
A57

4400E6EF1A57


4400
E6EF1A57

4
400E6EF1A57

4400E6EF1A
57

4
400E6EF1A57

4400E6EF1A5
7


4400E6EF1A57


4400E6EF1
A57

4400E6EF1A57



4400E
6EF1A57

4400
E6EF1A57

4400E6EF1A57


4400E6EF1A57



4400E6EF
1A57

4400E
6EF1A57

It appears to be that there is a long string of 0's and 1's that gets read in and only a few of those are the actual tag IDs. I don't know in what order I am reading these 0's and 1's.

Here is my code: (Some SQL and JDBC stuff incorporated, can ignore)

    import java.io.*;
    import java.util.*;
    import gnu.io.*;
    import java.sql.*;
 
 
    public class trying5 implements Runnable, SerialPortEventListener {
    static Enumeration portList;
    static CommPortIdentifier portId;
 
    SerialPort serialPort;
    InputStream inputStream;
    Thread readThread;
    Connection con;
 
    public static void main(String[] args) {
        portList = CommPortIdentifier.getPortIdentifiers();
        while (portList.hasMoreElements()) {
            portId = (CommPortIdentifier) portList.nextElement();
            if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {
                 if (portId.getName().equals("COM3")) {
                    trying5 reader = new trying5();
 
                }
            }
        }
    }
 
    public trying5()   {
 
 
        try {
            serialPort = (SerialPort) portId.open("trying5Application", 2000);
        	}
        	catch (PortInUseException e) 
 
        	{
        		System.out.println(e);
        	}
 
        try {
            inputStream = serialPort.getInputStream();
        	} 
        	catch (IOException e) 
 
        	{
        		System.out.println(e);
        	}
 
        try {
            serialPort.addEventListener(this);
        	} 
        	catch (TooManyListenersException e) 
 
        	{
        		System.out.println(e);
        	}
 
        	serialPort.notifyOnDataAvailable(true);
 
        try {
            serialPort.setSerialPortParams(9600,
                SerialPort.DATABITS_8,
                SerialPort.STOPBITS_1,
                SerialPort.PARITY_NONE);
 
        	} 
 
        catch (UnsupportedCommOperationException e) 
        	{
        		System.out.println(e);
        	}
 
        readThread = new Thread(this);
        readThread.start();
 
    	}
 
    public void run() {
        try {
            Thread.sleep(20000);
        	} 
        catch (InterruptedException e) 
        	{
        		System.out.println(e);
        	}
    }
 
    public void serialEvent(SerialPortEvent event) {
        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:
 
            byte[] readBuffer = new byte[20];
 
 
 
            // print to console
 
            try {
                while (inputStream.available() > 0) {
                    int numBytes = inputStream.read(readBuffer);
 
 
                }
 
 
 
                String newtuple = new String(readBuffer);
 
 
 
                usercon newcon = new usercon(con, newtuple);
 
                System.out.print(newtuple + "\n");
 
            } catch (IOException e) 
            {
            	System.out.println(e);
            }
            break;
        }
    }
    }

You're doing buffered IO, so you can't usually depend on reading complete transfers from your source. InputStream.available() tells you that *some* bytes are available, and you read them, emptying the buffer quicker than your source fills it. You hit the end of the buffer, available() returns false, and then your code prints the bytes-so-far followed by a newline. Your code needs to build up an internal buffer somehow of bytes that are marked by an end-of-transmission marker sent by the source. Looking at your output, I suspect that the source is sending its own newline. Try adding another println() that uses something like Arrays.toString(readBuffer) to see what individual bytes are being sent by the source.

Sorry if my reply is too late, I just joined this forum and the other members are so efficient, I had to look back a long way to find an unanswered question :p