Add quote in existing regex Java

Question

I have this existing regex : ^[_A-Za-z0-9-+]+(\\\\.[_A-Za-z0-9-]+)*

I want to add a quote in this regex. It can be anywhere and it must be present zero or only one time.

I haven't found what I need to add to be able to do this. Someone has an idea ?

Answer 1

You could add the ' to both character classes and start the pattern with a positive lookahead assertion for the presence of an optional ' anywhere in the string by making what is before and after the ' optional in the lookahead.

^(?=[\w.+-]*(?:'[\w.-]+)?$)[\w+'-]+(?:\.[\w-']+)*$

Explanation

• ^ Start of string
• (?= Positive lookahead, assert what is on the right is
  • [\\w.+-]* Match 0+ times any of [\\w.+-]*
  • (?:'[\\w.-]+)?$ Optionally match ' and 0+ times any of [\\w.-] and assert the end of the string.
• ) Close the lookahead
• [\\w+'-]+ Match 1+ word chars ' or -
• (?:\\.[\\w-']+)* Optionally repeat matching the previous preceded by a .
• $ End of string

Regex demo

In Java

String regex = "^(?=[\\w.+-]*(?:'[\\w.-]+)?$)[\\w+'-]+(?:\\.[\\w-']+)*$";