Java Regular Expressions - Validate IP Addresses

Check if IP Address is Valid Or Not with Java

Regular Expressions are widely-applicable and used to match patterns in text, whether for search, validation or other processing.

A common way to use them is to check whether a number is valid - i.e. follows a pattern. IP addresses follow a particular pattern, and can be tested with Regular Expressions.

This can also include validating Subnet masks, country-specific IPs, or any other criteria. In this example, we are just checking if a number is a valid IP or not:

public class RegexTutorial {
   public static void main(String[] args) {
       // Looking for a valid IP Address.
       Pattern pattern = Pattern.compile("^(([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.){3}([01]?\\d\\d?|2[0-4]\\d|25[0-5])$");
       Matcher matcher = pattern.matcher("192.168.1.1");
       boolean match = matcher.matches();
       System.out.println(match);
    }
}

The output will be:

true

This is a valid IP Address since this matches our criteria of 4 numbers separated by dots. All numbers are within the range of a valid IP Address too:

public class RegexTutorial {
    public static void main(String[] args) {
       // Looking for a valid IP Address.
        Pattern pattern = Pattern.compile("^(([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.){3}([01]?\\d\\d?|2[0-4]\\d|25[0-5])$");
        Matcher matcher = pattern.matcher("400.168.1.1");
        boolean match = matcher.matches();
        System.out.println(match);
    }
}

The output will be:

false

This is invalid since 400 is out of our IP Address range.