Validate IP Address with Java Regular Expression example

With this example we shall show you how to validate the format of ip addresses using Java Regular Expression. The basic format of ip addresses format policy is:

  • It must start with a number from 0 – 255.
  • It must be followed a dot
  • This pattern has to repeat for 4 times (eliminating the last dot…)

This is the regular expression used for ip address format validation:


You can take a look at the Pattern class documentation to learn how to construct your own regular expressions according to your policy.

1. Validator class

This is the class that we are going to use for ip address format validation.


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

public class IPAddressFormatValidator{

    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])\\." +

    public IPAddressFormatValidator(){
	  pattern = Pattern.compile(IPADDRESS_PATTERN);

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

2. Unit Testing our IPAddressFormatValidator class

For unit testing we are going to use JUnit. Unit testing is very important in these situations because they provide good feedback about the correctness of our regular expressions. You can test your program and reassure that your regular expression meets the rules on your policy about the form of the ip addresses.

This is a basic test class:


import static org.junit.Assert.*;

import java.util.Arrays;
import java.util.Collection;

import org.junit.BeforeClass;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.Parameterized;
import org.junit.runners.Parameterized.Parameters;

public class IPAddressFormatValidatorTest {

	private String arg;
	private static IPAddressFormatValidator iPAddressFormatValidator;
	private Boolean expectedValidation;

	public IPAddressFormatValidatorTest(String str, Boolean expectedValidation) {
		this.arg = str;
		this.expectedValidation = expectedValidation;

	public static void initialize() {
		iPAddressFormatValidator = new IPAddressFormatValidator();

	public static Collection<Object[]> data() {
		Object[][] data = new Object[][] {
				{ "192.102.100", false }, // must have a 4 '.' characters
				{ "a.b.c.d", false },     // you cannot have characters between '.'
				{ "", false },   // you can have only until 255
				{ "1.2.3", false },       // you must have 4 digit parts

				{ "",true },                         
				{ "", true },
				{ "", true } };

		return Arrays.asList(data);

	public void test() {
		Boolean res = iPAddressFormatValidator.validate(this.arg);
		String validv = (res) ? "valid" : "invalid";
		System.out.println("Hex Color Code "+arg+ " is " + validv);
		assertEquals("Result", this.expectedValidation, res);




Hex Color Code 192.102.100 is invalid
Hex Color Code a.b.c.d is invalid
Hex Color Code is invalid
Hex Color Code 1.2.3 is invalid
Hex Color Code is valid
Hex Color Code is valid
Hex Color Code is valid

This was an example on how to validate IP Address with Java Regular Expression.

Nikos Maravitsas

Nikos has graduated from the Department of Informatics and Telecommunications of The National and Kapodistrian University of Athens. During his studies he discovered his interests about software development and he has successfully completed numerous assignments in a variety of fields. Currently, his main interests are system’s security, parallel systems, artificial intelligence, operating systems, system programming, telecommunications, web applications, human – machine interaction and mobile development.
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