Java Regex IP Address Validation Example

IP Address Regex Pattern

^([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.
                           ([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.
                           ([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.
                           ([01]?\\d\\d?|2[0-4]\\d|25[0-5])$

^	Start of line
(	Start of group
[01]?\\d\\d?	Can be one or two digits. If three digits appear, it must start either 0 or 1
2[0-4]\\d	start with 2, follow by 0-4 and end with any digit
25[0-5]	start with 2, follow by 5 and end with 0-5 (25[0-5])
)	End of group
\.	follow by a dot
$	end of the line

Example

package mycollectiontest;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegexExample {
   private Pattern pattern;
   private Matcher matcher;
   private static final String IPADDRESS_PATTERN = "^([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." 
+ "([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\."
         + "([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\." + "([01]?\\d\\d?|2[0-4]\\d|25[0-5])$";

   public RegexExample() {
      pattern = Pattern.compile(IPADDRESS_PATTERN);
      String input = "12.12.12";
      System.out.println("input : " + input + " " + validate(input));

      String input1 = "180.151.46.166";
      System.out.println("input : " + input1 + " " + validate(input1));
   }

   public boolean validate(final String username) {
      matcher = pattern.matcher(username);
      return matcher.matches();

   }

   public static void main(String[] args) {
      new RegexExample();
   }
}

Output

input :  12.12.12   false

input :  180.151.46.166   true