Java正则表达式用点替换CSS类字符串中的空格

Question

Given a class attribute of an HTML element, I want to generate a String suitable for css selector.

For instance, the element's class attribute value:

'  foo bar  baz '

OR

'foo bar  baz '

Should both become a css selector:

'.foo.bar.baz'

Right now, I'm using:

String classCssSelector = "." + classProp.trim().replaceAll("\\s+", ".");

But I want to get rid of the leading hardcoded "." + "." + and the trim() and make it all one replaceAll call.

EDIT :

I used the regex provided in @anubhava's answer, but then wanted it to also match an already 'dotted' class like this:

'  foo bar  baz '

The following regex works for both cases:

^(?!\.)| +(?= *\S) 

Answer 1

You can use this regex in replaceAll :

^ *| +(?= *\S)

RegEx Demo

Code:

String classCssSelector = classProp.replaceAll("^ *| +(?= *\\S)", ".");

Explanation:

^         - Match beginning
^ *       - Match 0 or more spaces at start
|         - Alternation in regex
| +       - Match 1 more spaces after `|`
(?= *\\S) - Lookahead to make sure there is at least one non-space character after matching
            space in previous match