javax.comm 以及如何修复 java.lang.NoClassDefFoundError

Question

我正在为移动设备创建一个 midlet。该 midlet 正在访问 com4 端口。我已经将 javax.comm 添加到 jre1.6.0、jre6 和 jdk1.6.0 文件夹（在 lib\ext 中）。

我的项目文件夹中名为 lib 的文件夹中还有 javax.comm.jar ，并在构建路径中引用了它。

操作系统：Windows 7。
手机：中国移动。
IDE：安装了eclipseME1.8的eclipse。

当我在 Eclipse 中运行该项目时，它给了我这个错误：

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)

我知道 javax.comm 在 64x Windows 上不起作用，但为什么当我在设备中安装 jar 时它不起作用？没有错误消息或者只是这样：“jar 文件已终止。”
所以我去谷歌搜索答案，找到了适用于 Windows x86 和 x64 的 txrx，但我不知道这是否适用于移动设备中的 Midlet。因为他们已经为 Windows 提供了这一点。那么我该如何解决这个问题呢？这里是 midlet 类代码，仅供记录：

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");
}
    }

还有一件事，接口 SerialPortEventListener 继承自 java.util.EventListener，而我的 java.util 包没有。基本上，我将 java.util 和 java.io 不需要的任何内容添加到 src 文件夹中，并将每个内容添加到单独的文件（和包）中。他们在这里：

//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

您在移动端使用了错误的 API - 这就是为什么您会遇到所有这些 NoClassDefFoundError 消息和 java.util 中其他缺失内容的原因。

在 MIDP (JSR 118) 设备上，应该使用 javax.microedition.io .CommConnection API 通过串口进行通信。