Here is a minimalist Java code which can be used to test if a port is available.

In this example, we are checking for port 8080 by opening a new Socket to that port. We allow up to 10 retries if the port has been found already used. Enjoy it!

import java.io.IOException;
import java.net.Socket;

public class Portchecker {
    private static boolean available(int port) {
        System.out.println("--------------Testing port " + port);
        Socket s = null;
        try {
            s = new Socket("localhost", port);

            // If the code makes it this far without an exception it means
            // something is using the port and has responded.
            System.out.println("--------------Port " + port + " is not available");
            return false;
        } catch (IOException e) {
            System.out.println("--------------Port " + port + " is available");
            return true;
        } finally {
            if (s != null) {
                try {
                    s.close();
                } catch (IOException e) {
                    throw new RuntimeException("You should handle this error.", e);
                }
            }
        }
    }

    public static void main(String[] args) {
        int attempts = 0;
        boolean scanning = true;
        while (scanning) {

            if (!available(8080)) {
                attempts++;
                if (attempts == 10) {
                    System.out.println("giving up!");
                    scanning = false;
                }
            } else {
                scanning = false;
            }

            try {
                Thread.sleep(2000);// 2 seconds
            } catch (InterruptedException ie) {
                ie.printStackTrace();
            }

        }

    }

}
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