Email Regular Expression Pattern

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

Description

^			#start of the line
  [_A-Za-z0-9-\\+]+	#  must start with string in the bracket [ ], must contains one or more (+)
  (			#   start of group #1
    \\.[_A-Za-z0-9-]+	#     follow by a dot "." and string in the bracket [ ], must contains one or more (+)
  )*			#   end of group #1, this group is optional (*)
    @			#     must contains a "@" symbol
     [A-Za-z0-9-]+      #       follow by string in the bracket [ ], must contains one or more (+)
      (			#         start of group #2 - first level TLD checking
       \\.[A-Za-z0-9]+  #           follow by a dot "." and string in the bracket [ ], must contains one or more (+)
      )*		#         end of group #2, this group is optional (*)
      (			#         start of group #3 - second level TLD checking
       \\.[A-Za-z]{2,}  #           follow by a dot "." and string in the bracket [ ], with minimum length of 2
      )			#         end of group #3
$			#end of the line

The combination means, email address must start with “_A-Za-z0-9-\\+” , optional follow by “.[_A-Za-z0-9-]“, and end with a “@” symbol. The email’s domain name must start with “A-Za-z0-9-”, follow by first level Tld (.com, .net) “.[A-Za-z0-9]” and optional follow by a second level Tld (.com.au, .com.my) “\\.[A-Za-z]{2,}”, where second level Tld must start with a dot “.” and length must equal or more than 2 characters.

1. Java Regular Expression Example

Here’s a Java example to show you how to use regex to validate email address.

EmailValidator.java
package com.mkyong.regex;
 
import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
public class EmailValidator {
 
	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 EmailValidator() {
		pattern = Pattern.compile(EMAIL_PATTERN);
	}
 
	/**
	 * Validate hex with regular expression
	 * 
	 * @param hex
	 *            hex for validation
	 * @return true valid hex, false invalid hex
	 */
	public boolean validate(final String hex) {
 
		matcher = pattern.matcher(hex);
		return matcher.matches();
 
	}
}

2. Valid Emails

1. [email protected], [email protected], [email protected]
2. [email protected], [email protected], [email protected]
3. [email protected], [email protected]
4. [email protected], [email protected]

3. Invalid Emails

1. mkyong – must contains “@” symbol
2. mkyong@.com.my – tld can not start with dot “.”
3. [email protected] – “.a” is not a valid tld, last tld must contains at least two characters
4. mkyong123@.com – tld can not start with dot “.”
5. mkyong123@.com.com – tld can not start with dot “.”
6. .[email protected] – email’s first character can not start with dot “.”
7. mkyong()*@gmail.com – email’s is only allow character, digit, underscore and dash
8. mkyong@%*.com – email’s tld is only allow character and digit
9. mkyong..[email protected] – double dots “.” are not allow
10. mkyong.@gmail.com – email’s last character can not end with dot “.”
11. mkyong@mkyong@gmail.com – double “@” is not allow
12. [email protected] -email’s tld which has two characters can not contains digit

4. Unit Test

Here’s a unit test using testNG.

EmailValidatorTest.java
package com.mkyong.regex;
 
import org.testng.Assert;
import org.testng.annotations.*;
 
/**
 * Email validator Testing
 * 
 * @author mkyong
 * 
 */
public class EmailValidatorTest {
 
	private EmailValidator emailValidator;
 
	@BeforeClass
	public void initData() {
		emailValidator = new EmailValidator();
	}
 
	@DataProvider
	public Object[][] ValidEmailProvider() {
		return new Object[][] { { new String[] { "[email protected]",
			"[email protected]", "[email protected]",
			"[email protected]", "[email protected]",
			"[email protected]", "[email protected]",
			"[email protected]", "[email protected]",
			"[email protected]" } } };
	}
 
	@DataProvider
	public Object[][] InvalidEmailProvider() {
		return new Object[][] { { new String[] { "mkyong", "mkyong@.com.my",
			"[email protected]", "mkyong123@.com", "mkyong123@.com.com",
			".[email protected]", "mkyong()*@gmail.com", "mkyong@%*.com",
			"mkyong..[email protected]", "mkyong.@gmail.com",
			"mkyong@mkyong@gmail.com", "[email protected]" } } };
	}
 
	@Test(dataProvider = "ValidEmailProvider")
	public void ValidEmailTest(String[] Email) {
 
		for (String temp : Email) {
			boolean valid = emailValidator.validate(temp);
			System.out.println("Email is valid : " + temp + " , " + valid);
			Assert.assertEquals(valid, true);
		}
 
	}
 
	@Test(dataProvider = "InvalidEmailProvider", dependsOnMethods = "ValidEmailTest")
	public void InValidEmailTest(String[] Email) {
 
		for (String temp : Email) {
			boolean valid = emailValidator.validate(temp);
			System.out.println("Email is valid : " + temp + " , " + valid);
			Assert.assertEquals(valid, false);
		}
	}
}

Here’s the unit test result.

Email is valid : mkyong@yahoo.com , true
Email is valid : mkyong-100@yahoo.com , true
Email is valid : mkyong.100@yahoo.com , true
Email is valid : mkyong111@mkyong.com , true
Email is valid : mkyong-100@mkyong.net , true
Email is valid : mkyong.100@mkyong.com.au , true
Email is valid : mkyong@1.com , true
Email is valid : mkyong@gmail.com.com , true
Email is valid : mkyong+100@gmail.com , true
Email is valid : mkyong-100@yahoo-test.com , true
Email is valid : mkyong , false
Email is valid : mkyong@.com.my , false
Email is valid : mkyong123@gmail.a , false
Email is valid : mkyong123@.com , false
Email is valid : mkyong123@.com.com , false
Email is valid : .mkyong@mkyong.com , false
Email is valid : mkyong()*@gmail.com , false
Email is valid : mkyong@%*.com , false
Email is valid : mkyong..2002@gmail.com , false
Email is valid : mkyong.@gmail.com , false
Email is valid : mkyong@mkyong@gmail.com , false
Email is valid : mkyong@gmail.com.1a , false
PASSED: ValidEmailTest([Ljava.lang.String;@15f48262)
PASSED: InValidEmailTest([Ljava.lang.String;@789934d4)
 
===============================================
    Default test
    Tests run: 2, Failures: 0, Skips: 0
===============================================

References

  1. http://en.wikipedia.org/wiki/E-mail_address
  2. http://tools.ietf.org/html/rfc2822#section-3.4.1
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