Java - Writing to serial port using Java Communication API

import java.io.IOException;

import java.io.OutputStream;

import java.util.Enumeration;

import javax.comm.CommPortIdentifier;

import javax.comm.PortInUseException;

import javax.comm.SerialPort;

import javax.comm.UnsupportedCommOperationException;

/**

 *

 * @author dhanoopbhaskar

 */

public class SerialPortWriter {

    Enumeration portList;
    CommPortIdentifier portIdentifier;
    String message;
    SerialPort serialPort;
    OutputStream outputStream;
    String portName = "";

    public SerialPortWriter(String portName) {
        this.portName = portName;
        /**
         * gets a list of ports
         */
        portList = CommPortIdentifier.getPortIdentifiers();


        while (portList.hasMoreElements()) {

            portIdentifier = (CommPortIdentifier) portList.nextElement();
            /**
             * check whether the port is serial
             */
            if (portIdentifier.getPortType() == CommPortIdentifier.PORT_SERIAL) {

                /**
                 * check whether the port name is portName (eg.COM1)
                 */
                if (portIdentifier.getName().equals(portName)) {
                    try {
                        /**
                         * String - application name
                         * int - time out value
                         */
                        serialPort = (SerialPort) portIdentifier.open("SerialPortWriter", 2000);
                    } catch (PortInUseException ex) {
                        System.out.println("#1 " + ex);
                    }

                    try {
                        outputStream = serialPort.getOutputStream();
                    } catch (IOException ex) {
                        System.out.println("#2 " + ex);
                    }

                    try {
                        /**
                         * int baudrate
                         * int dataBits
                         * int stopBits
                         * int parity
                         */
                        serialPort.setSerialPortParams(9600,
                                SerialPort.DATABITS_8,
                                SerialPort.STOPBITS_1,
                                SerialPort.PARITY_NONE);

                        serialPort.setDTR(true);
                    } catch (UnsupportedCommOperationException ex) {
                        System.out.println("#3 " + ex);
                    }
                }
            }
        }
    }

    public void sendMessage(String message) {

        try {
            outputStream.write(message.getBytes());
        } catch (IOException ex) {
            System.out.println(ex);
        }
    }

    public void close() {
        serialPort.close();
    }
}

To test the above program you need to download Java Communication API.

Download Java Comm API - click here

After the download has completed extract the archive and you will get the following files, and it is very important to have them installed on your system for a proper operation:

• comm.jar
• win32com.dll
• javax.comm.properties

comm.jar should be placed in:

    %JAVA_HOME%/lib

    %JAVA_HOME%/jre/lib/ext

win32com.dll should be placed in:

    %JAVA_HOME%/bin

    %JAVA_HOME%/jre/bin

    %windir%System32

javax.comm.properties should be placed in:

    %JAVA_HOME%/lib

    %JAVA_HOME%/jre/lib