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 Email Address with Java Regular Expression example

Email validation is a very frequent requirement in many applications. Basically the main policy that email format follows is that it:

  • Has to start with characters, digits or ‘_’, ‘-’, ‘+’ symbols
  • The above group can be followed with a ‘.’ and the same pattern as the first group.
  • Then it must have exactly one ‘@’ character.
  • The domain name must start with characters, digits and the ‘-’ character.
  • Then it must be followed by a ‘.’.
  • After the ‘.’ you can have characters and digits.
  • Optionally you  can have a second level Top Level Domain that can start with a ‘.’ and the contain only characters.

This is the regular expression used for email validation:

^[_A-Za-z0-9-\\+]+(\\.[_A-Za-z0-9-]+)*@[A-Za-z0-9-]+(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$

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 email format validation.

EmailFormatValidator.java:

package com.javacodegeeks.java.core;

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

public class EmailFormatValidator {

	private Pattern pattern;
	private Matcher matcher;

	private static final String EMAIL_PATTERN = "^[_A-Za-z0-9-\\+]+(\\.[_A-Za-z0-9-]+)*@"
			+ "[A-Za-z0-9-]+(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$";

	public EmailFormatValidator() {
		pattern = Pattern.compile(EMAIL_PATTERN);
	}

	public boolean validate(final String email) {

		matcher = pattern.matcher(email);
		return matcher.matches();

	}
}

2. Unit Testing our EmailFormatValidator 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 email addresses.

This is a basic test class:

EmailFormatValidatorTest.java:

package com.javacodegeeks.java.core;

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;

@RunWith(Parameterized.class)
public class EmailFormatValidatorTest {

	private String arg;
	private static EmailFormatValidator emailFormatValidator;
	private Boolean expectedValidation;

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

	@BeforeClass
	public static void initialize() {
		emailFormatValidator = new EmailFormatValidator();
	}

	@Parameters
	public static Collection<Object[]> data() {
		Object[][] data = new Object[][] {
				{ "javacodegeeks@gmail.com.2j",false },    // it's not allowed to have a digit in the second level tld
				{ "java@java@oracle.com", false },         // you cannot have @ twice in the address
				{ "java!!!@example.com", false },          // you cannot the have special character '!' in the address
				{ "mysite@.com", false },                  // tld cannot start with a dot
				{ "javacodegees.com", false },             // must contain a @ character and a tld
				{ ".javacodegees.com@at.com", false },     // the address cannot start with a dot
				{ "javacodegees..javacom@at.com", false }, // you cannot have double dots in your address


				{ "javacodegeeks@gmail.com",true },                         
				{ "nikos+mylist@gmail.com", true },
				{ "abc.efg-900@gmail-list.com", true },
				{ "abc123@example.com.gr", true } };

		return Arrays.asList(data);
	}

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

	}

}

Output:

Hex Color Code javacodegeeks@gmail.com.2j is invalid
Hex Color Code java@java@oracle.com is invalid
Hex Color Code java!!!@example.com is invalid
Hex Color Code mysite@.com is invalid
Hex Color Code javacodegees.com is invalid
Hex Color Code .javacodegees.com@at.com is invalid
Hex Color Code javacodegees..javacom@at.com is invalid
Hex Color Code javacodegeeks@gmail.com is valid
Hex Color Code nikos+mylist@gmail.com is valid
Hex Color Code abc.efg-900@gmail-list.com is valid
Hex Color Code abc123@example.com.gr is valid

 
This was an example on how to perform email address format validation with Java Regular Expression.

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