Question

I’m creating a midlet for a mobile. This midlet is accessing the com4 port. I already added the javax.comm to jre1.6.0, jre6 and jdk1.6.0 folders (in lib\ext).

I also have the javax.comm.jar in a folder named lib in my project folder and referenced it in build path.

os: windows 7.
mobile: china mobile.
IDE: eclipse with eclipseME1.8 installed.

when I run the project in eclipse it’s giving me this error:

java.lang.NoClassDefFoundError: MainMidlet: javax/comm/SerialPortEventListener 
    at com.sun.midp.midlet.MIDletState.createMIDlet(+29)
    at com.sun.midp.midlet.Scheduler.schedule(+52)
    at com.sun.midp.main.Main.runLocalClass(+28)
    at com.sun.midp.main.Main.main(+80)

I know that the javax.comm will not work on 64x windows, but why when I install the jar in the device it doesn’t work? no error message either just this: “the jar file is terminated.”
So I went to google and searched for answer and found txrx for windows x86 and x64 but I don’t know if this is working for a Midlet in a mobile device. Since they have been provided that for windows. So how do I get around this? here is the midlet class code just for the record:

import javax.microedition.lcdui.*;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
import javax.comm.*;
import java.util.*;
import java.io.*;

public class MainMidlet extends MIDlet implements CommandListener,
    SerialPortEventListener {
// displaying this midlet
private Display display;
private Form form;
private StringItem stringItem;
private Command exitCommand;
// serial vars
private CommPortIdentifier portId;
private Enumeration portList;
private InputStream inputStream;
private SerialPort serialPort;
private Thread readThread;

public MainMidlet() {
    portList = CommPortIdentifier.getPortIdentifiers();
    while (portList.hasMoreElements()) {
        portId = (CommPortIdentifier) portList.nextElement();
        if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {
            if (portId.getName().equals("COM4")) {
                this.AttachToCom();
            }
        }
    }
}

protected void destroyApp(boolean arg0) throws MIDletStateChangeException {
    // TODO Auto-generated method stub

}

protected void pauseApp() {
    // TODO Auto-generated method stub

}

public void commandAction(Command command, Displayable displayable) {
    if (displayable == form) {
        if (command == exitCommand) {
            exitMIDlet();
        }
    }
}

public void startApp() {
    stringItem = new StringItem("Hello", "Serial app is running!");
    form = new Form(null, new Item[] { stringItem });
    exitCommand = new Command("Exit", Command.EXIT, 1);
    form.addCommand(exitCommand);
    form.setCommandListener(this);
    display = Display.getDisplay(this);
    display.setCurrent(form);
}

public void exitMIDlet() {
    display.setCurrent(null);
    notifyDestroyed();
}

public void serialEvent(SerialPortEvent ev) {
    print("serialEvent is called.");
    switch (ev.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];
        try {
            while (inputStream.available() > 0) {
                inputStream.read(readBuffer);
            }
            print(new String(readBuffer));
        } catch (IOException e) {
            print(e.getMessage());
        }
        break;
    }
}

private void AttachToCom() {
    try {
        serialPort = (SerialPort) portId.open("MyProject", 2000);
    } catch (PortInUseException e) {
        print(e.getMessage());
    }
    try {
        inputStream = serialPort.getInputStream();
    } catch (IOException e) {
        print(e.getMessage());
    }
    try {
        serialPort.addEventListener(this);
    } catch (TooManyListenersException e) {
        print(e.getMessage());
    }
    serialPort.notifyOnDataAvailable(true);
    try {
        serialPort.setSerialPortParams(9600, SerialPort.DATABITS_8,
                SerialPort.STOPBITS_1, SerialPort.PARITY_NONE);
    } catch (UnsupportedCommOperationException e) {
        print(e.getMessage());
    }
    readThread = new Thread((Runnable) this);
    readThread.start();
}

private void print(String str) {
    form.append(str + "\r\n");
}
    }

There is also one more thing, the interface SerialPortEventListener inherits from java.util.EventListener which my java.util package doesn’t have. Basically I added whatever my java.util and java.io don’t have to the src folder and each in a separate file (and package). Here they are:

//the file is named EventListener.java and in a package named java.util
package java.util;
/**
* A tagging interface that all event listener interfaces must extend.
* @since JDK1.1
*/
public interface EventListener {
} 

//the file is named EventObject.java and in a package named java.util
//removed the comment to minimize this post
package java.util;

// removed the comment to minimize this post
public class EventObject implements java.io.Serializable {

private static final long serialVersionUID = 5516075349620653480L;

// The object on which the Event initially occurred.
protected transient Object source;

// removed the comment to minimize this post
public EventObject(Object source) {
    if (source == null)
        throw new IllegalArgumentException("null source");

    this.source = source;
}
// removed the comment to minimize this post
public Object getSource() {
    return source;
}
public String toString() {
    return getClass().getName() + "[source=" + source + "]";
}
}
// the file is named TooManyEventListenersException.java and in a package named java.util
// removed comment to reduce this post size

package java.util;

// removed comment to reduce this post size
public class TooManyListenersException extends Exception {
    // removed comment to reduce this post size
    public TooManyListenersException() {
        super();
    }
    // removed comment to reduce this post size
    public TooManyListenersException(String s) {
        super(s);
    }
}    
// in the file named Serializable.java and in a package java.io
package java.io;
public interface Serializable {
}

Answer 1

You are using wrong API at mobile side – that’s why you’re stuck with all these NoClassDefFoundError messages and other missing stuff in java.util.

At MIDP (JSR 118) devices one should use javax.microedition.io .CommConnection API to communicate via serial port.