How to validate password with regular expression

Password Regular Expression Pattern

((?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%]).{6,20})

Description

(			# Start of group
  (?=.*\d)		#   must contains one digit from 0-9
  (?=.*[a-z])		#   must contains one lowercase characters
  (?=.*[A-Z])		#   must contains one uppercase characters
  (?=.*[@#$%])		#   must contains one special symbols in the list "@#$%"
              .		#     match anything with previous condition checking
                {6,20}	#        length at least 6 characters and maximum of 20	
)			# End of group

?= – means apply the assertion condition, meaningless by itself, always work with other combination

Whole combination is means, 6 to 20 characters string with at least one digit, one upper case letter, one lower case letter and one special symbol (“@#$%”). This regular expression pattern is very useful to implement a strong and complex password.

P.S The grouping formula order is doesn’t matter.

1. Java Regular Expression Example

PasswordValidator.java

package com.mkyong.regex;
 
import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
public class PasswordValidator{
 
	  private Pattern pattern;
	  private Matcher matcher;
 
	  private static final String PASSWORD_PATTERN = 
              "((?=.*\\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%]).{6,20})";
 
	  public PasswordValidator(){
		  pattern = Pattern.compile(PASSWORD_PATTERN);
	  }
 
	  /**
	   * Validate password with regular expression
	   * @param password password for validation
	   * @return true valid password, false invalid password
	   */
	  public boolean validate(final String password){
 
		  matcher = pattern.matcher(password);
		  return matcher.matches();
 
	  }
}

2. Password that match:

1. mkyong1A@
2. mkYOn12$

3. Password that doesn’t match:

1. mY1A@ , too short, minimum 6 characters
2. mkyong12@ , uppercase characters is required
3. mkyoNg12* , special symbol “*” is not allow here
4. mkyonG$$, digit is required
5. MKYONG12$ , lower case character is required

4. Unit Test – PasswordValidator

Unit test with TestNG.

PasswordValidatorTest.java

package com.mkyong.regex;
 
import org.testng.Assert;
import org.testng.annotations.*;
 
/**
 * Password validator Testing
 * @author mkyong
 *
 */
public class PasswordValidatorTest {
 
	private PasswordValidator passwordValidator;
 
	@BeforeClass
        public void initData(){
		passwordValidator = new PasswordValidator();
        }
 
	@DataProvider
	public Object[][] ValidPasswordProvider() {
		return new Object[][]{
		   {new String[] {
			   "mkyong1A@", "mkYOn12$", 
		   }}
	        };
	}
 
	@DataProvider
	public Object[][] InvalidPasswordProvider() {
		return new Object[][]{
		   {new String[] {
			   "mY1A@","mkyong12@","mkyoNg12*",
                            "mkyonG$$","MKYONG12$"	  
		   }}
	       };
	}
 
	@Test(dataProvider = "ValidPasswordProvider")
	public void ValidPasswordTest(String[] password) {
 
	   for(String temp : password){
		boolean valid = passwordValidator.validate(temp);
		System.out.println("Password is valid : " + temp + " , " + valid);
		Assert.assertEquals(true, valid);
	   }
 
	}
 
	@Test(dataProvider = "InvalidPasswordProvider", 
                 dependsOnMethods="ValidPasswordTest")
	public void InValidPasswordTest(String[] password) {
 
	   for(String temp : password){
		boolean valid = passwordValidator.validate(temp);
		System.out.println("Password is valid : " + temp + " , " + valid);
		Assert.assertEquals(false, valid);
	   }
	}
}

5. Unit Test – Result

Password is valid : mkyong1A@ , true
Password is valid : mkYOn12$ , true
Password is valid : mY1A@ , false
Password is valid : mkyong12@ , false
Password is valid : mkyoNg12* , false
Password is valid : mkyonG$$ , false
Password is valid : MKYONG12$ , false
PASSED: ValidPasswordTest([Ljava.lang.String;@1d4c61c)
PASSED: InValidPasswordTest([Ljava.lang.String;@116471f)
 
===============================================
    com.mkyong.regex.PasswordValidatorTest
    Tests run: 2, Failures: 0, Skips: 0
===============================================
 
 
===============================================
mkyong
Total tests run: 2, Failures: 0, Skips: 0
===============================================