How to close the COM Port ??????????

Question

Dear all :
I have written an application that send AT commands to a modem , Once I opened a com port , i don't know how to close it . I got the null pointer exception when i create a new channel , because the inputStream and outputStream is owned by the previous channel . So , some one can teach me how to close the com port that opened before ?
my source code for open port :
public void Connect_Com(CommPortIdentifier portId) {
Integer i = new Integer((int) (Math.random()* 1000));
String channel = "channel" + i.toString();
System.out.println(channel);
try {
System.out.println("preparing to open port");
serialPort = (SerialPort) portId.open(channel, 2000);
} catch (PortInUseException e) {}
try {
inputStream = serialPort.getInputStream();
System.out.println("getting inputStream");
          } catch (IOException e) {}
try {
serialPort.addEventListener(this);
          } catch (TooManyListenersException e) {}
serialPort.notifyOnDataAvailable(true);
try {
serialPort.setSerialPortParams(9600,
SerialPort.DATABITS_8,
SerialPort.STOPBITS_1,
SerialPort.PARITY_NONE);
} catch (UnsupportedCommOperationException e) {}

Answer 1

serialPort.close() ?
From the documentation of SerialPort:
- SerialPort extends CommPort.
- CommPort.close() closes the communications port.