How to validate username with regular expression

Username Regular Expression Pattern

 ^[a-z0-9_-]{3,15}$

Description

^                    # Start of the line
  [a-z0-9_-]	     # Match characters and symbols in the list, a-z, 0-9 , underscore , hyphen
             {3,15}  # Length at least 3 characters and maximum length of 15 
$                    # End of the line

Whole combination is means, 3 to 15 characters with any lower case character, digit or special symbol “_-” only. This is common username pattern that’s widely use in different websites.

Example in Java

package com.mkyong.regex;
 
import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
public class UsernameValidator{
 
	  private Pattern pattern;
	  private Matcher matcher;
 
	  private static final String USERNAME_PATTERN = "^[a-z0-9_-]{3,15}$";
 
	  public UsernameValidator(){
		  pattern = Pattern.compile(USERNAME_PATTERN);
	  }
 
	  /**
	   * Validate username with regular expression
	   * @param username username for validation
	   * @return true valid username, false invalid username
	   */
	  public boolean validate(final String username){
 
		  matcher = pattern.matcher(username);
		  return matcher.matches();
 
	  }
}

Username that match:

1) mkyong34
2) mkyong_2002
3) mkyong-2002
4) mk3-4_yong

Username that doesn’t match:

1) mk (too short, min 3 characters)
2) mk@yong (“@” character is not allow)
3) mkyong123456789_- (too long, max characters of 15)

Unit Test – UsernameValidator

package com.mkyong.regex;
 
import org.testng.Assert;
import org.testng.annotations.*;
 
/**
 * Username validator Testing
 * @author mkyong
 *
 */
public class UsernameValidatorTest {
 
	private UsernameValidator usernameValidator;
 
	@BeforeClass
    public void initData(){
		usernameValidator = new UsernameValidator();
    }
 
	@DataProvider
	public Object[][] ValidUsernameProvider() {
		return new Object[][]{
				   {new String[] {
						   "mkyong34", "mkyong_2002","mkyong-2002" ,"mk3-4_yong"
				   }}
				  };
	}
 
	@DataProvider
	public Object[][] InvalidUsernameProvider() {
		return new Object[][]{
				   {new String[] {
						   "mk","mk@yong","mkyong123456789_-"	  
				   }}
				  };
	}
 
	@Test(dataProvider = "ValidUsernameProvider")
	public void ValidUsernameTest(String[] Username) {
 
	   for(String temp : Username){
		   boolean valid = usernameValidator.validate(temp);
		   System.out.println("Username is valid : " + temp + " , " + valid);
		   Assert.assertEquals(true, valid);
	   }
 
	}
 
	@Test(dataProvider = "InvalidUsernameProvider", dependsOnMethods="ValidUsernameTest")
	public void InValidUsernameTest(String[] Username) {
 
	   for(String temp : Username){
		   boolean valid = usernameValidator.validate(temp);
		   System.out.println("username is valid : " + temp + " , " + valid);
		   Assert.assertEquals(false, valid);
	   }
 
	}	
}

Unit Test – Result

Username is valid : mkyong34 , true
Username is valid : mkyong_2002 , true
Username is valid : mkyong-2002 , true
Username is valid : mk3-4_yong , true
username is valid : mk , false
username is valid : mk@yong , false
username is valid : mkyong123456789_- , false
PASSED: ValidUsernameTest([Ljava.lang.String;@1d4c61c)
PASSED: InValidUsernameTest([Ljava.lang.String;@116471f)
 
===============================================
    com.mkyong.regex.UsernameValidatorTest
    Tests run: 2, Failures: 0, Skips: 0
===============================================
 
 
===============================================
mkyong
Total tests run: 2, Failures: 0, Skips: 0
===============================================

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