Port Availability Scanner, written in Java (9)

Question

For purpose of practice and experience, I was working on a "Port Availability Scanner" written in Java. So far it's working but it's really slow. Especially on relatively large quantities of ports (1000+).

It's quite faster scanning localhost then my external IP (If it actually scans externally correctly).

As an additional note for if it really matters: I am using Java 9.

Code:

package test;

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

public class Test {

    private static final Test instance = new Test("157.97.56.42", 80, 443, 21, 22, 25, 8080);
    private static String ip;
    private int[] ports = new int[1_000_000];

    private Test(String ip, int start, int end) {
        Test.ip = ip;

        ports: {
            int c = 0;

            for (int i = start; i < end; i++) {
                ports[c++] = i;
            }

            ports = Arrays.copyOfRange(ports, 0, c + 1);
        }
    }

    private Test(String ip, int... ports) {
        Test.ip = ip;
        this.ports = ports;
    }

    public static void main(String[] args) {
        long start = System.currentTimeMillis();
        Thread thread = new Thread(instance::check);
        thread.start();
        long end = System.currentTimeMillis();

        System.out.println("Took: " + (end - start) + "ms.");
    }

    public void check() {
        if(ports.length > 1) {
            for (int port : ports) {
                System.out.println("Available " + port + ": " + Test.isAvailable(port));
            }
        } else if(ports.length == 1) {
            System.out.println("Available " + ports[0] + ": " + Test.isAvailable(ports[0]));
        } else {
            throw new IllegalStateException();
        }
    }

    private static boolean isAvailable(int port) {
        Socket socket = null;

        try {
            socket = new Socket(ip, port);
            return false;
        } catch (IOException e) {
            return true;
        } finally {
            if(socket != null) {
                try {
                    socket.close();
                } catch (IOException ignored) { }
            }
        }
    }
}

Please can you review my code, especially performance-wise?

Edit: Would it be possible by using NIO or any other form of MultiThreading the sake of speed?

Answer 1

1. Why do you create a million element array? (int[] ports = new int[1_000_000]) It'd better to make it as large as the ports in constructor (end-start or ports.length)

2. Why all of this code?

   if(ports.length > 1) {
       for (int port : ports) {
           System.out.println("Available " + port + ": " + Test.isAvailable(port));
       }
   } else if(ports.length == 1) {
       System.out.println("Available " + ports[0] + ": " + Test.isAvailable(ports[0]));
   } else {
       throw new IllegalStateException();
   }
   

   You only really need

   for (int port : ports) {
       System.out.println("Available " + port + ": " + Test.isAvailable(port));
   }
   

   The result will be equivalent and the code is now more readable

3. Why did you make ip and instance static? Do you want to make the class a singleton?

4. The ports label is unnecessary in the first constructor

5. Use InetAddress instead of String for IPs' as from what I know Sockets convert the strings into InetAdresses anyway. It should somewhat improve performance (change ip variable from String to InetAddress so you don't recreate the address on and on again)

6. Shouldn't this:

   try {
       socket = new Socket(ip, port);
       return false;
   } catch (IOException e) {
       return true;
   } finally {
       if(socket != null) {
           try {
               socket.close();
           } catch (IOException ignored) { }
       }
   }
   

   work the other way round? Why method isAvailable returns true when the socket throws a exception? Looks like a bug to me I misunderstood what you meant by available. Your code is correct