我需要帮助使用ftdi usb到串行电缆写入/读取串行端口

Question

I want to first write to serial port. for that i am using a usb to serial ftdi cable. The cable is connected to COM4. Running Windows 7 64-bit

a) Using the RXTX project. http://rxtx.qbang.org/wiki/index.php/Main_Page

To utilize the RXTX I tried doing that by following these instructions

1. download rxtx-2.1-7-bins-r2.zip
2. unzip it
3. copy rxtxSerial.dll into c:\\program files\\java\\jre-version\\bin dir
4. copy RXTXcomm.jar into c:\\program files\\java\\jre-version\\lib\\ext dir
5. change all references from 'javax.comm' to 'gnu.io'
6. recompile

Here is my code:

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package twowayserialcomm;

/**
 *
 * @author HP
 */

import java.io.InputStream;
import java.io.OutputStream;
import gnu.io.SerialPort;
import gnu.io.CommPortIdentifier;
import gnu.io.CommPort;

public class TwoWaySerialComm {

    /**
     * @param args the command line arguments
     * 
     */
    void connect( String portName ) throws Exception {
        CommPortIdentifier portIdentifier = CommPortIdentifier.getPortIdentifier( portName );

        if( portIdentifier.isCurrentlyOwned() ) {
            System.out.println( "Error: Port is currently in use" );
        } else {
            int timeout = 10000;
            CommPort commPort = portIdentifier.open( this.getClass().getName(), timeout );

            if( commPort instanceof SerialPort ) {
                SerialPort serialPort = ( SerialPort )commPort;
                serialPort.setSerialPortParams( 9600,
                                    SerialPort.DATABITS_8,
                                    SerialPort.STOPBITS_1,
                                    SerialPort.PARITY_NONE );

                //InputStream in = serialPort.getInputStream();
                OutputStream outputStream = serialPort.getOutputStream();
                outputStream.write( 53 ); 
                //outputStream.write( 1 ); 
                //outputStream.write( 20 ); 
                //outputStream.write( 0 ); 
                //outputStream.write( 83 );

                //CommPort port = serialPort;
                System.out.println( "Write done" );
                //( new Thread( new SerialReader( in,port  ) ) ).start();
            } else {
                System.out.println( "Error: Only serial ports are handled by this example." );
            }
        }
    }
    public static void main(String[] args) {
        try {
            TwoWaySerialComm alex = new TwoWaySerialComm();
            //( new TwoWaySerialComm() ).connect( "COM4" );
            alex.connect("COM4");
        } catch( Exception e ) {
            e.printStackTrace();
        }
    }
}

When running:

run:
java.lang.UnsatisfiedLinkError: no rxtxSerial in java.library.path thrown while loading gnu.io.RXTXCommDriver
Exception in thread "main" java.lang.UnsatisfiedLinkError: no rxtxSerial in java.library.path
    at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1867)
    at java.lang.Runtime.loadLibrary0(Runtime.java:870)
    at java.lang.System.loadLibrary(System.java:1122)
    at gnu.io.CommPortIdentifier.<clinit>(CommPortIdentifier.java:83)
    at twowayserialcomm.TwoWaySerialComm.connect(TwoWaySerialComm.java:26)
    at twowayserialcomm.TwoWaySerialComm.main(TwoWaySerialComm.java:61)
C:\Users\HP\AppData\Local\NetBeans\Cache\8.1\executor-snippets\run.xml:53: Java returned: 1
BUILD FAILED (total time: 1 second)

b) by using the javax.comm. libraries When doing that i got following erros

run:
javax.comm.NoSuchPortException
    at javax.comm.CommPortIdentifier.getPortIdentifier(CommPortIdentifier.java:105)
    at twowayserialcomm.TwoWaySerialComm.connect(TwoWaySerialComm.java:26)
    at twowayserialcomm.TwoWaySerialComm.main(TwoWaySerialComm.java:61)

and here is the project window from netbeans

Serial Port Java

Answer 1

The error that you get means that the dll could not be found in java.library.path , so you need to set the system property java.library.path to the path corresponding to the folder that contains the library, by adding -Djava.library.path="C:\\path\\to\\your\\dll" as VM Options

More details about how to set the path to a dll in NetBeans