java看不到连接的设备COM4

java没有在COM4上看到arudino，代码似乎正在运行

package tester;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStream;
import gnu.io.CommPortIdentifier; 
import gnu.io.SerialPort;
import gnu.io.SerialPortEvent; 
import gnu.io.SerialPortEventListener; 
import java.util.Enumeration;
public class SerialTest implements SerialPortEventListener {
SerialPort serialPort;
    /** The port we're normally going to use. */
private static final String PORT_NAMES[] = { 
        "/dev/tty.usbserial-A9007UX1", // Mac OS X
                    "/dev/ttyACM0", // Raspberry Pi
        "/dev/ttyUSB0", // Linux
        "COM4", // Windows
};
/**
* A BufferedReader which will be fed by a InputStreamReader 
* converting the bytes into characters 
* making the displayed results codepage independent
*/
private BufferedReader input;
/** The output stream to the port */
private OutputStream output;
/** Milliseconds to block while waiting for port open */
private static final int TIME_OUT = 2000;
/** Default bits per second for COM port. */
private static final int DATA_RATE = 9600;

public void initialize() {
            // the next line is for Raspberry Pi and 
            // gets us into the while loop and was suggested here was       suggested http://www.raspberrypi.org/phpBB3/viewtopic.php?f=81&t=32186
            System.setProperty("gnu.io.rxtx.SerialPorts", "/dev/ttyACM0");

    CommPortIdentifier portId = null;
    Enumeration portEnum = CommPortIdentifier.getPortIdentifiers();

    //First, Find an instance of serial port as set in PORT_NAMES.
    while (portEnum.hasMoreElements()) {
        CommPortIdentifier currPortId = (CommPortIdentifier) portEnum.nextElement();
        for (String portName : PORT_NAMES) {
            if (currPortId.getName().equals(portName)) {
                portId = currPortId;
                break;
            }
        }
    }
    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 = new BufferedReader(new InputStreamReader(serialPort.getInputStream()));
        output = serialPort.getOutputStream();

        // add event listeners
        serialPort.addEventListener(this);
        serialPort.notifyOnDataAvailable(true);
    } catch (Exception e) {
        System.err.println(e.toString());
    }
}

/**
 * This should be called when you stop using the port.
 * This will prevent port locking on platforms like Linux.
 */
public synchronized void close() {
    if (serialPort != null) {
        serialPort.removeEventListener();
        serialPort.close();
    }
}

/**
 * Handle an event on the serial port. Read the data and print it.
 */
public synchronized void serialEvent(SerialPortEvent oEvent) {
    if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE) {
        try {
            String inputLine=input.readLine();
            System.out.println(inputLine);
        } catch (Exception e) {
            System.err.println(e.toString());
        }
    }
    // Ignore all the other eventTypes, but you should consider the other ones.
}

public static void main(String[] args) throws Exception {
    SerialTest main = new SerialTest();
    main.initialize();
    Thread t=new Thread() {
        public void run() {
            //the following line will keep this app alive for 1000 seconds,
            //waiting for events to occur and responding to them (printing incoming messages to console).
            try {Thread.sleep(1000000);} catch (InterruptedException ie) {}
        }
    };
    t.start();
    System.out.println("Started");
}}

似乎在工作，但我在控制台里得到的只是

WARNING:  RXTX Version mismatch
Jar version = RXTX-2.2pre1
native lib Version = RXTX-2.2pre2
Could not find COM port.
Started

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我看到jar版本已经关闭，但rxtx在稳定的版本中要求它

为什么你认为它在windows上总是“COM4”？可能尝试像这样获取com端口（从）：

公共静态列表getSerialPorts（）{ List vp=new ArrayList（）； 枚举端口列表=CommPortIdentifier.getPortIdentifiers（）； while（portList.hasMoreElements（））{ CommPortIdentifier portId=（CommPortIdentifier）portList.nextElement（）； if（portId.getPortType（）==CommPortIdentifier.PORT_串行）{ add（portId.getName（））； } } 返回vp； }

---

作为RxTx和（不推荐使用的）Java通信API的替代品，我很幸运

我制作了一个对话框，下拉选择127个com端口（不带保留端口），作为让应用程序知道正在使用哪个com端口的第一件事。然后在下一个新类实例的构造函数中使用它

public static List<String> getSerialPorts(){
  List<String> vp=new ArrayList<String>();
  Enumeration portList=CommPortIdentifier.getPortIdentifiers();
  while (portList.hasMoreElements()) {
    CommPortIdentifier portId=(CommPortIdentifier)portList.nextElement();
    if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {
      vp.add(portId.getName());
    }
  }
  return vp;
}