使用 Java 正则表达式的密码验证失败

Question

My requirements include among other things to validate for the password input to include one of the following characters only once. ?@#$%^&*()_+=?~

To accomplish that I wrote the following:

StringBuilder builder = new StringBuilder("(?=.*[a-z])");
builder.append("(?=.{1}[!@#$%^&*()_+=?~])");

Pattern pattern = Pattern.compile(builder.toString());
Matcher matcher = pattern.matcher(input);

if(matcher.matches){
    return True;
}

But this always fails when I pass valid input in my unit test. I am new to regex.

Answer 1

You may use this regex with 2 lookahead assertions:

^(?=[^a-z]*[a-z])(?=[^!@#$%^&*()_+=?~]*[!@#$%^&*()_+=?~][^!@#$%^&*()_+=?~]*$).{12,}$

RegEx Demo

Note that in .matches() method start & end anchors are automatically implied in a given regex.

RegEx Details:

• ^ : Start
• (?=[^az]*[az]) : Positive lookahead to make sure we have at least one lowercase letter
• (?=[^?@#$%^&*()_+=?~]*[?@#$%^&*()_+=?~][^!@#$%^&*()_+=?~]*$) : Positive lookahead to make sure we have ONLY one of the given special character.
• .{12,} : Match min 12 of any characters
• $ : End