为什么使用 RXTX 编译此 J2ME 代码时会出现错误？

Question

我用 Sun Java ME Platform SDK 3.0 编译了这段代码，该代码将侦听串行端口：

import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import gnu.io.SerialPortEvent;
import gnu.io.SerialPortEventListener;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Enumeration;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.TextField;
import javax.microedition.midlet.*;

public class SerialPortMidlet extends MIDlet implements CommandListener, SerialPortEventListener
{
    private Command download = new Command("download", Command.ITEM, 0);
    private Command exit = new Command("exit", Command.ITEM, 1);
    private Form f = new Form("test serial port");
    private TextField ports = new TextField("data : ","",1000,TextField.ANY);
    private static final String PORT_NAMES = "COM4";
    private SerialPort serialPort;
    private InputStream input;
    private OutputStream output;
    private static final int TIME_OUT = 2000;
    private static final int DATA_RATE = 9600;

    public SerialPortMidlet()
    {
        f.append(ports);
        f.addCommand(download);
        f.addCommand(exit);
        f.setCommandListener(this);
    }
    public void startApp() {
        Display.getDisplay(this).setCurrent(f);
        initialize();
    }
    public void pauseApp() {
    }
    public void destroyApp(boolean unconditional) {
        notifyDestroyed();
    }
    public void commandAction(Command c, Displayable d) {
        if (c == exit)
            destroyApp(true);
    }
    public void initialize() {
        CommPortIdentifier portId = null;
        Enumeration portEnum = CommPortIdentifier.getPortIdentifiers();
        while (portEnum.hasMoreElements()) {
            CommPortIdentifier currPortId = (CommPortIdentifier) portEnum.nextElement();
            if (currPortId.getName().equals(PORT_NAMES)) {
                portId = currPortId;
            }
        }
        if (portId == null) {
                System.out.println("Could not find COM port.");
                return;
        }
        try
        {
            // open serial port, and use class name for the appName.
            serialPort = (SerialPort) portId.open(this.getClass().getName(), TIME_OUT);

            // set port parameters
            serialPort.setSerialPortParams( DATA_RATE,
                                            SerialPort.DATABITS_8,
                                            SerialPort.STOPBITS_1,
                                            SerialPort.PARITY_NONE );

            // open the streams
            input = serialPort.getInputStream();
            output = serialPort.getOutputStream();

            // add event listeners
            serialPort.addEventListener(this);
            serialPort.notifyOnDataAvailable(true);
        }
        catch (Exception e) {
                System.err.println(e.toString());
        }
    }
    public synchronized void close() {
        if (serialPort != null) {
            serialPort.removeEventListener();
            serialPort.close();
        }
    }
    public void serialEvent(SerialPortEvent oEvent) {
        if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE)
        {
            try {
                    int available = input.available();
                    byte chunk[] = new byte[available];
                    input.read(chunk, 0, available);

                    // Displayed results are codepage dependent
                    ports.setString(new String(chunk));
                    System.out.print(new String(chunk));
            } catch (Exception e) {
                    System.err.println(e.toString());
            }
        }
    }
}

输出显示：

pre-init:
pre-load-properties:
exists.config.active:
exists.netbeans.user:
exists.user.properties.file:
load-properties:
exists.platform.active:
exists.platform.configuration:
exists.platform.profile:
basic-init:
cldc-pre-init:
cldc-init:
cdc-init:
bdj-init:
post-init:
init:
conditional-clean-init:
conditional-clean:
pre-clean:
clean-timestamp:
clean-preprocessed:
clean-classes:
Deleting directory C:\Documents and Settings\Ambre-28\Mes documents\JavaMESDKProjects\testPortSerie\build\compiled
clean-obfuscated:
clean-preverified:
clean-manifest:
clean-jar:
clean-jad:
clean-javadoc:
clean-j9:
Deleting: C:\Documents and Settings\Ambre-28\Mes documents\JavaMESDKProjects\testPortSerie\convert883343865
post-clean:
do-clean:
clean:
deps-jar:
pre-preprocess:
do-preprocess:
post-preprocess:
preprocess:
pre-compile:
extract-libs:
Created dir: C:\Documents and Settings\Ambre-28\Mes documents\JavaMESDKProjects\testPortSerie\build\compiled
Expanding: D:\rxtx-2.1-7-bins-r2\RXTXcomm.jar into C:\Documents and Settings\Ambre-28\Mes documents\JavaMESDKProjects\testPortSerie\build\compiled
do-compile:
Compiling 1 source file to C:\Documents and Settings\Ambre-28\Mes documents\JavaMESDKProjects\testPortSerie\build\compiled
C:\Documents and Settings\Ambre-28\Mes documents\JavaMESDKProjects\testPortSerie\src\SerialPortMidlet.java:16: cannot access java.util.EventListener
class file for java.util.EventListener not found
public class SerialPortMidlet extends MIDlet implements CommandListener, SerialPortEventListener
C:\Documents and Settings\Ambre-28\Mes documents\JavaMESDKProjects\testPortSerie\src\SerialPortMidlet.java:34: cannot find symbol
symbol  : variable this
location: class SerialPortMidlet
        f.setCommandListener(this);
C:\Documents and Settings\Ambre-28\Mes documents\JavaMESDKProjects\testPortSerie\src\SerialPortMidlet.java:37: cannot find symbol
symbol  : variable this
location: class SerialPortMidlet
        Display.getDisplay(this).setCurrent(f);
C:\Documents and Settings\Ambre-28\Mes documents\JavaMESDKProjects\testPortSerie\src\SerialPortMidlet.java:65: cannot find symbol
symbol  : variable this
location: class SerialPortMidlet
            serialPort = (SerialPort) portId.open(this.getClass().getName(), TIME_OUT);
C:\Documents and Settings\Ambre-28\Mes documents\JavaMESDKProjects\testPortSerie\src\SerialPortMidlet.java:78: cannot find symbol
symbol  : variable this
location: class SerialPortMidlet
            serialPort.addEventListener(this);
C:\Documents and Settings\Ambre-28\Mes documents\JavaMESDKProjects\testPortSerie\src\SerialPortMidlet.java:92: cannot access java.util.EventObject
class file for java.util.EventObject not found
        if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE)
6 errors
C:\Documents and Settings\Ambre-28\Mes documents\JavaMESDKProjects\testPortSerie\nbproject\build-impl.xml:246: Compile failed; see the compiler error output for details.
BUILD FAILED (total time: 7 seconds)

系统是 Windows XP 并且我已经将 RXTXcomm.jar 添加到 图书馆与图书馆项目属性的资源。那么为什么会出现这些错误呢？

Answer 1

与 J2SE 不同，您不能使用外部 dll 或 JNI 来扩展 J2ME VM 的功能集。 VM 由供应商或 OEM 提供，并发布其支持级别（例如 JTWI 合规性等）。所以，简而言之，使用Rxtx库无法获得串口访问。

但是，串行端口可以通过通用 I/O 框架访问：

CommConnection sc = (CommConnection)Connector.open("comm:0;baudrate=9600");

但是，对通信的支持是可选的，供应商可能不会实现它。您需要交叉检查设备的文档。