JAVA: Serial Port access with javax.comm or rxtx on Windows, Linux etc.

import java.io.*;
import java.util.*;
//import javax.comm.*; // for SUN's serial/parallel port libraries
import gnu.io.*; // for rxtxSerial library

public class nulltest implements Runnable, SerialPortEventListener {
static CommPortIdentifier portId;
static CommPortIdentifier saveportId;
static Enumeration portList;
InputStream inputStream;
SerialPort serialPort;
Thread readThread;

static String messageString = "Hello, world!";
static OutputStream outputStream;
static boolean outputBufferEmptyFlag = false;

public static void main(String[] args) {
boolean portFound = false;
String defaultPort;

// determine the name of the serial port on several operating systems
String osname = System.getProperty("os.name","").toLowerCase();
if ( osname.startsWith("windows") ) {
// windows
defaultPort = "COM1";
} else if (osname.startsWith("linux")) {
// linux
defaultPort = "/dev/ttyS0";
} else if ( osname.startsWith("mac") ) {
// mac
defaultPort = "????";
} else {
System.out.println("Sorry, your operating system is not supported");
return;
}

if (args.length > 0) {
defaultPort = args[0];
}

System.out.println("Set default port to "+defaultPort);

// parse ports and if the default port is found, initialized the reader
portList = CommPortIdentifier.getPortIdentifiers();
while (portList.hasMoreElements()) {
portId = (CommPortIdentifier) portList.nextElement();
if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {
if (portId.getName().equals(defaultPort)) {
System.out.println("Found port: "+defaultPort);
portFound = true;
// init reader thread
nulltest reader = new nulltest();
}
}

}
if (!portFound) {
System.out.println("port " + defaultPort + " not found.");
}

}

public void initwritetoport() {
// initwritetoport() assumes that the port has already been opened and
// initialized by "public nulltest()"

try {
// get the outputstream
outputStream = serialPort.getOutputStream();
} catch (IOException e) {}

try {
// activate the OUTPUT_BUFFER_EMPTY notifier
serialPort.notifyOnOutputEmpty(true);
} catch (Exception e) {
System.out.println("Error setting event notification");
System.out.println(e.toString());
System.exit(-1);
}

}

public void writetoport() {
System.out.println("Writing /""+messageString+"/" to "+serialPort.getName());
try {
// write string to serial port
outputStream.write(messageString.getBytes());
} catch (IOException e) {}
}

public nulltest() {
// initalize serial port
try {
serialPort = (SerialPort) portId.open("SimpleReadApp", 2000);
} catch (PortInUseException e) {}

try {
inputStream = serialPort.getInputStream();
} catch (IOException e) {}

try {
serialPort.addEventListener(this);
} catch (TooManyListenersException e) {}

// activate the DATA_AVAILABLE notifier
serialPort.notifyOnDataAvailable(true);

try {
// set port parameters
serialPort.setSerialPortParams(9600, SerialPort.DATABITS_8,
SerialPort.STOPBITS_1,
SerialPort.PARITY_NONE);
} catch (UnsupportedCommOperationException e) {}

// start the read thread
readThread = new Thread(this);
readThread.start();

}

public void run() {
// first thing in the thread, we initialize the write operation
initwritetoport();
try {
while (true) {
// write string to port, the serialEvent will read it
writetoport();
Thread.sleep(1000);
}
} catch (InterruptedException e) {}
}

public void serialEvent(SerialPortEvent event) {
switch (event.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:
// we get here if data has been received
byte[] readBuffer = new byte[20];
try {
// read data
while (inputStream.available() > 0) {
int numBytes = inputStream.read(readBuffer);
}
// print data
String result = new String(readBuffer);
System.out.println("Read: "+result);
} catch (IOException e) {}

break;
}
}

}