Java string validation using regex

Question

I need to validate an input string using regex.

The requirement is:

The input

1. must not start with % , _

2. must not contain & , # , > , <

3. may be empty

I have used [^%_#&<>][^#&<>]*|^$ successfully.

Is there any better way to address the problem?

Answer 1

Your regex is wrong, you should also place ^ and $ constraints on the first variant:

^[^%_#&<>][^#&<>]*|$

This because the first case can be applied on a substring .

The regex you defined simply states: an empty string, or a string with at least one character that is not % , _ , # ,...

It think the proposed regex is good enough. Some (probably not java) regex libraries offer additional functionality to state that the string should not contain a certain character. But since the regex is not that complex, it won't help that much.