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.

1. Java Regular Expression Example

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();
	    	    
	  }
}

2. Username that match:

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

3. 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)

4. Unit Test – UsernameValidator

Using testNG to perform unit test.

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);
	   }
	   
	}	
}

5. 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
===============================================