Java Class for verifying minimum password standard.

PasswordValidator.java

public class PasswordValidator {
	
	// For character determinations
    private static final int CHAR_LOWER_A = 'a';
    private static final int CHAR_LOWER_Z = 'z';
    private static final int CHAR_UPPER_A = 'A';
    private static final int CHAR_UPPER_Z = 'Z';
    private static final int CHAR_NUMERIC_ZERO = '0';
    private static final int CHAR_NUMERIC_NINE = '9';

    // Since the alpha and numeric checks handle the [a-zA-Z0-9] case in
    // earlier if statement checks, we can then assume the surrounding characters
    // within the range of the special char lower and upper values are in fact
    // special characters.  If it extends past the range, then it's no longer a symbol.
    private static final int CHAR_LOWER_SPECIAL_CHAR = ' ';
    private static final int CHAR_UPPER_SPECIAL_CHAR = '~';
    
    // Configurable variables
    private static int minPasswordLength = 8;
    private static int maxPasswordLength = 255;
    private static int minLowerAlphaChars = 1;
    private static int minUpperAlphaChars = 1;
    private static int minSpecialChars = 1;
    private static int minNumericalChars = 1;

    // Override the default values
    public static synchronized void configure(int newMinPasswordLength, int newMaxPasswordLength,
            int newMinLowerAlphaChars, int newMinUpperAlphaChars, int newMinSpecialChars,
            int newMinNumericalChars) {

        minPasswordLength = newMinPasswordLength;
        maxPasswordLength = newMaxPasswordLength;
        minLowerAlphaChars = newMinLowerAlphaChars;
        minUpperAlphaChars = newMinUpperAlphaChars;
        minSpecialChars = newMinSpecialChars;
        minNumericalChars = newMinNumericalChars;
    }
    
    public static String validatePassword(String password){
    	int alphaLowerCharsCount = 0;
        int alphaUpperCharsCount = 0;
        int numericCharsCount = 0;
        int specialCharsCount = 0;

        String message = ""; // the error message
        
        if(password == null){
        	message = message+"Password cannot be null. It should follow the guidelines.\n\n";
        }
        if (password.length() < minPasswordLength) {
            message = message+"The password must be at least " + minPasswordLength + " characters in length.\n\n";
        }
        if (password.length() > maxPasswordLength) {
        	message = message+"The password must be at less than " + maxPasswordLength + " characters in length.\n\n";
        }
        
        // Count the characters
        char passwordChar;
        for (int i = 0; i < password.length(); i++) {
            passwordChar = password.charAt(i);
            // check for lower character
            if (passwordChar >= CHAR_LOWER_A && passwordChar <= CHAR_LOWER_Z) {
                alphaLowerCharsCount++;
            } 
            // check for upper character
            else if (passwordChar >= CHAR_UPPER_A && passwordChar <= CHAR_UPPER_Z) {
                alphaUpperCharsCount++;
            } 
            // check for special character
            else if (passwordChar >= CHAR_NUMERIC_ZERO && passwordChar <= CHAR_NUMERIC_NINE) {
                numericCharsCount++;
            } 
            else if (passwordChar >= CHAR_LOWER_SPECIAL_CHAR && passwordChar <= CHAR_UPPER_SPECIAL_CHAR) {
            	specialCharsCount++;
            }
            else {
                message = message+"Invalid password character entered.  You can only use: a-z, A-Z, 0-9, Symbols [such as: !, @, #]\n\n";
            }
        }

        if (alphaLowerCharsCount < minLowerAlphaChars) {
            message = message+"The password must contain at least " + minLowerAlphaChars + " lowercase alphabets (a-z) characters.\n\n";
        }
        if (alphaUpperCharsCount < minUpperAlphaChars) {
        	message = message+"The password must contain at least " + minUpperAlphaChars + " uppercase alphabets (A-Z) characters.\n\n";
        }
        if (numericCharsCount < minNumericalChars) {
            message = message+"The password must contain at least " + minNumericalChars + " numerical (0-9) characters.\n\n";
        }
        if (specialCharsCount < minSpecialChars) {
            message = message+"The password must contain at least " + minSpecialChars + " special (symbols such as: !, @, #) characters.\n\n";
        }        
        return message;
    }
	
}