Java program to monitor a web server. To use, type in Monitor <web address> <frequency> <timeout>

Monitor.java

import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;

public class Monitor {

	public static void main(String[] args) throws IOException {
		if (args.length < 3)
			throw new IllegalArgumentException("Invalid number of arguments");

		String webAddress = args[0];
		
		int frequency  = 0;
		int timeout = 0;
		try {
			frequency = Integer.parseInt(args[1]);
		} catch (NumberFormatException e) {
			throw new IllegalArgumentException("Invalid value for frequency: " + args[1]);
		}
		
		try {
			timeout = Integer.parseInt(args[2]);
		} catch (NumberFormatException e) {
			throw new IllegalArgumentException("Invalid value for timeout: " + args[2]);
		}
		
		URL url = new URL(webAddress);
		    
		while (true) {
			HttpURLConnection conn = (HttpURLConnection) url.openConnection();
			long startTime = System.currentTimeMillis();
			conn.connect();
			conn.getInputStream();
			conn.setConnectTimeout(timeout);

			int responseCode = conn.getResponseCode();
			if (responseCode == HttpURLConnection.HTTP_OK) {
				long responseTime = System.currentTimeMillis() - startTime;
				System.out.println("Response time: " + responseTime + "ms");
			} else {
				System.out.println("Server access error");
			}

			conn.disconnect();
			try {
				Thread.sleep(frequency);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}

}