Nikos Maravitsas

About Nikos Maravitsas

Nikos has graduated from the Department of Informatics and Telecommunications of The National and Kapodistrian University of Athens. 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.

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.

Do you want to know how to develop your skillset to become a Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you two of our best selling eBooks for FREE!

JPA Mini Book

Learn how to leverage the power of JPA in order to create robust and flexible Java applications. With this Mini Book, you will get introduced to JPA and smoothly transition to more advanced concepts.

JVM Troubleshooting Guide

The Java virtual machine is really the foundation of any Java EE platform. Learn how to master it with this advanced guide!

Given email address is already subscribed, thank you!
Oops. Something went wrong. Please try again later.
Please provide a valid email address.
Thank you, your sign-up request was successful! Please check your e-mail inbox.
Please complete the CAPTCHA.
Please fill in the required fields.
Examples Java Code Geeks and all content copyright © 2010-2015, Exelixis Media Ltd | Terms of Use | Privacy Policy | Contact
All trademarks and registered trademarks appearing on Examples Java Code Geeks are the property of their respective owners.
Java is a trademark or registered trademark of Oracle Corporation in the United States and other countries.
Examples Java Code Geeks is not connected to Oracle Corporation and is not sponsored by Oracle Corporation.
Do you want to know how to develop your skillset and become a ...
Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you two of our best selling eBooks for FREE!

Get ready to Rock!
You can download the complementary eBooks using the links below: