Regexp Java for password validation

Thanks for all answers, based on all them but extending sphecial characters:

@SuppressWarnings({"regexp", "RegExpUnexpectedAnchor", "RegExpRedundantEscape"})
String PASSWORD_SPECIAL_CHARS = "@#$%^`<>&+=\"!ºª·#~%&'¿¡€,:;*/+-.=_\\[\\]\\(\\)\\|\\_\\?\\\\";
int PASSWORD_MIN_SIZE = 8;
String PASSWORD_REGEXP = "^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[" + PASSWORD_SPECIAL_CHARS + "])(?=\\S+$).{"+PASSWORD_MIN_SIZE+",}$";

Unit tested:

For anyone interested in minimum requirements for each type of character, I would suggest making the following extension over Tomalak's accepted answer:

^(?=(.*[0-9]){%d,})(?=(.*[a-z]){%d,})(?=(.*[A-Z]){%d,})(?=(.*[^0-9a-zA-Z]){%d,})(?=\S+$).{%d,}$

Notice that this is a formatting string and not the final regex pattern. Just substitute %d with the minimum required occurrences for: digits, lowercase, uppercase, non-digit/character, and entire password (respectively). Maximum occurrences are unlikely (unless you want a max of 0, effectively rejecting any such characters) but those could be easily added as well. Notice the extra grouping around each type so that the min/max constraints allow for non-consecutive matches. This worked wonders for a system where we could centrally configure how many of each type of character we required and then have the website as well as two different mobile platforms fetch that information in order to construct the regex pattern based on the above formatting string.

This one checks for every special character :

^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=\S+$).*[A-Za-z0-9].{8,}$

Java Method ready for you, with parameters

Just copy and paste and set your desired parameters.

If you don't want a module, just comment it or add an "if" as done by me for special char

//______________________________________________________________________________
/**
 * Validation Password     */
//______________________________________________________________________________
private static boolean validation_Password(final String PASSWORD_Arg)    {
    boolean result = false;
    try {
        if (PASSWORD_Arg!=null) {
            //_________________________
            //Parameteres
            final String MIN_LENGHT="8";
            final String MAX_LENGHT="20";
            final boolean SPECIAL_CHAR_NEEDED=true;

            //_________________________
            //Modules
            final String ONE_DIGIT = "(?=.*[0-9])";  //(?=.*[0-9]) a digit must occur at least once
            final String LOWER_CASE = "(?=.*[a-z])";  //(?=.*[a-z]) a lower case letter must occur at least once
            final String UPPER_CASE = "(?=.*[A-Z])";  //(?=.*[A-Z]) an upper case letter must occur at least once
            final String NO_SPACE = "(?=\\S+$)";  //(?=\\S+$) no whitespace allowed in the entire string
            //final String MIN_CHAR = ".{" + MIN_LENGHT + ",}";  //.{8,} at least 8 characters
            final String MIN_MAX_CHAR = ".{" + MIN_LENGHT + "," + MAX_LENGHT + "}";  //.{5,10} represents minimum of 5 characters and maximum of 10 characters

            final String SPECIAL_CHAR;
            if (SPECIAL_CHAR_NEEDED==true) SPECIAL_CHAR= "(?=.*[@#$%^&+=])"; //(?=.*[@#$%^&+=]) a special character must occur at least once
            else SPECIAL_CHAR="";
            //_________________________
            //Pattern
            //String pattern = "(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=])(?=\\S+$).{8,}";
            final String PATTERN = ONE_DIGIT + LOWER_CASE + UPPER_CASE + SPECIAL_CHAR + NO_SPACE + MIN_MAX_CHAR;
            //_________________________
            result = PASSWORD_Arg.matches(PATTERN);
            //_________________________
        }    

    } catch (Exception ex) {
        result=false;
    }

    return result;
}        

Also You Can Do like This.

 public boolean isPasswordValid(String password) {


    String regExpn =
            "^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=])(?=\\S+$).{8,}$";

    CharSequence inputStr = password;

    Pattern pattern = Pattern.compile(regExpn,Pattern.CASE_INSENSITIVE);
    Matcher matcher = pattern.matcher(inputStr);

    if(matcher.matches())
        return true;
    else
        return false;
}

Use Passay library which is powerful api.

Sample code block for strong password:

(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[^a-zA-Z0-9])(?=\\S+$).{6,18}

1. at least 6 digits
2. up to 18 digits
3. one number
4. one lowercase
5. one uppercase
6. can contain all special characters

RegEx is -

^(?:(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*)[^\s]{8,}$

1. at least 8 digits {8,}
2. at least one number (?=.*\d)
3. at least one lowercase (?=.*[a-z])
4. at least one uppercase (?=.*[A-Z])
5. at least one special character (?=.*[@#$%^&+=])
6. No space [^\s]

A more general answer which accepts all the special characters including _ would be slightly different:

^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[\W|\_])(?=\S+$).{8,}$

The difference (?=.*[\W|\_]) translates to "at least one of all the special characters including the underscore".