How to check whether a port is being used or not in Java

Problem Description

How to check whether a port is being used or not?

Solution

Following example shows how to check whether any port is being used as a server or not by creating a socket object.

import java.net.*;
import java.io.*;

public class Main {
   public static void main(String[] args) {
      Socket Skt;
      String host = "localhost";
      
      if (args.length > 0) {
         host = args[0];
      }
      for (int i = 0; i < 1024; i++) {
         try {
            System.out.println("Looking for "+ i);
            Skt = new Socket(host, i);
            System.out.println("There is a server on port " + i + " of " + host);
         } catch (UnknownHostException e) {
            System.out.println("Exception occured"+ e);
            break;
         } catch (IOException e) {}
      }
   }
}

Result

The above code sample will produce the following result.

Looking for 0
Looking for 1
Looking for 2
Looking for 3
Looking for 4. . .