如何在Java中访问端口?

我正在尝试使用以下Java代码访问系统中的端口，并且给出了空指针异常，任何人都可以帮助我解决此问题.拜托，在此先谢谢

I am trying to access ports in system by using below java code And it is giving null pointer exception can anyone help me to solve this . Please , Thanks in advance

package com.ranju.app;

import java.util.Enumeration;

import javax.comm.CommPortIdentifier;

public class Ranjith {

public static void main(String[] args) {

System.out.println("HI ");
Enumeration pList= CommPortIdentifier.getPortIdentifiers();
System.out.println(" ++++++++ ");
//while(pList.hasMoreElements()){
CommPortIdentifier commIdfr=(CommPortIdentifier) pList.nextElement();
System.out.println(" *** "+commIdfr.getName());

//}
}

}