Pattern Matching for Password

Java introduced Pattern matching API from JDK 1.4 onwards. Its definitely a wonderful API for validating passwords, userId, etc in an application. There are some predefined regular expressions available. Here, Iam going to explain a regular expression for password validation.

You would have encountered password rules in several websites. Lets see how the regular expression is going to be for the following password rule:
It should contain at least one digit from 0-9
It should contain at least one letter from A-Z
It should not contain any lower case letter
The minimum length of the username must be 6 characters and the maximum may be 20.
It should contain at least one character from amongst @#*=
It should not contain any spaces

Regular Expression for the above conditions :

• (?=.*[@#*=]) # must contains one special character "@#$%"
• (?=.*[A-Z]) # must contains one UPPER Case Character
• (?!.*[a-z]) # must not contain lower case Character (See ! instead of =)
• (?=.*[0-9]) # must contains one number 0-9
• (?!.*\\s) # must not contain any spaces
• . # match anything with previous condition checking
• {6,20} # length at least 6 characters and maximum of 20

Java Pattern Matching Code:

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

public class UserName
{
public static void main(String[] args)
{
  String password="ABC3a#@@";
  Pattern pattern = Pattern.compile("(?=.*[@#*=])(?=.*[A-Z])(?!.*[a-z])(?=.*[0-9])(?!.*\\s).{6,20}$");
  Matcher m = pattern.matcher(userName);
  boolean b = m.matches();
  if (b==false)
    System.out.println("FAIL");
  else if(b==true)
    System.out.println("PASS");
}
}