Java Regex match space before or after characters

I try to have a regex validating an input field.

This question is the continuation of this question but I made a mistake and the question changed a bit so I created a new one.

Here is my java regex :

^(?:\?*[a-zA-Z\d]){2}[a-zA-Z\d?]*\*?$

Demo

What I'm tying to match is :

Minimum 2 alpha-numeric characters (other than '?' and '*')
The '*' can only appears one time and at the end of the string
The '?' can appears multiple time
No WhiteSpace right at the beginning
No WhiteSpace before or after '?' or '*'

So for exemple :

abcd = OK

?bcd = OK

ab?? = OK

ab*= OK

ab?* = OK

??cd = OK

ab cd = OK

*ab = NOT OK

a ? b =NOT OK

??? = NOT OK

ab? cd = NOT OK

ab ?d = NOT OK

ab * = NOT OK

abcd = NOT OK (space at the begining)

As i've asked in the fisrt question, no white space at all are allowed in my regex now but that's not what I want and I'm a bit lost can you help me please?

Solution

You may use

^(?!\s)(?!.*\s[*?])(?!.*[*?]\s)(?:[?\s]*[a-zA-Z0-9]){2}[a-zA-Z0-9?\s]*\*?$

See the regex demo.

Usage note: if you use it with Java's .matches() method, the ^ and $ can be removed from the pattern. Remember to double escape backslashes in the string literal.

Details

^ - start of string
(?!\s) - no whitespace is allowed immediately to the right (at the start of the string)
(?!.*\s[*?]) - no whitespace is allowed after any 0+ chars, as many as possible, before * or ?
(?!.*[*?]\s) - no whitespace is allowed after any 0+ chars, as many as possible, after * or ?
(?:[?\s]*[a-zA-Z0-9]){2} - two sequences of
- [?\s]* - 0 or more ? or/and whitespaces
- [a-zA-Z0-9] - an alphanumeric char
[a-zA-Z0-9?\s]* - 0 or more letters, digits, ? or whitespaces
\*? - an optional ? char
$ - end of the string.