Java Regex hung on a long string

Question

I am trying to write a REGEX to validate a string. It should validate to the requirement which is that it should have only Uppercase and lowercase English letters (a to z, A to Z) (ASCII: 65 to 90, 97 to 122) AND/OR Digits 0 to 9 (ASCII: 48 to 57) AND Characters - _ ~ (ASCII: 45, 95, 126). Provided that they are not the first or last character. It can also have Character. (dot, period, full stop) (ASCII: 46) Provided that it is not the first or last character, and provided also that it does not appear two or more times consecutively. I have tried using the following

Pattern.compile("^[^\\W_*]+((\\.?[\\w\\~-]+)*\\.?[^\\W_*])*$");

It works fine for smaller strings but it doesn't for long strings as i am experiencing thread hung issues and huge spikes in cpu. Please help.

Test cases for invalid strings:

"aB78."
"aB78..ab"
"aB78,1"
"aB78 abc"
".Abc12"

Test cases for valid strings:

"abc-def"
"a1b2c~3"
"012_345"

Answer 1

As @MarounMaroun already commented, you don't really have a pattern. It might be better to iterate over the string as in the following method:

public static boolean validate(String string) {
    char chars[] = string.toCharArray();

    if (!isSpecial(chars[0]) && !isLetterOrDigit(chars[0]))
        return false;
    if (!isSpecial(chars[chars.length - 1])
            && !isLetterOrDigit(chars[chars.length - 1]))
        return false;
    for (int i = 1; i < chars.length - 1; ++i)
        if (!isPunctiation(chars[i]) && !isLetterOrDigit(chars[i])
                && !isSpecial(chars[i]))
            return false;
    return true;
}

public static boolean isPunctiation(char c) {
    return c == '.' || c == ',';
}

public static boolean isSpecial(char c) {
    return c == '-' || c == '_' || c == '~';
}

public static boolean isLetterOrDigit(char c) {
    return (Character.isDigit(c) || (Character.isLetter(c) && (Character
            .getType(c) == Character.UPPERCASE_LETTER || Character
            .getType(c) == Character.LOWERCASE_LETTER)));
}

Test code:

public static void main(String[] args) {
    System.out.println(validate("aB78."));
    System.out.println(validate("aB78..ab "));
    System.out.println(validate("abcdef"));
    System.out.println(validate("aB78,1"));
    System.out.println(validate("aB78 abc"));
}

Output:

false
false
true
true
false