How to match with optional occurence?

Question

For the construct {123{a,b}} I want to match {123{ and }} .

This is done by regex: {(.*?){|}}

BUT: now I want to use the same expression to run on {a,b} and match { and } only.

Therefore I somehow have to make the 2nd { optional. But how?

I'm using http://gskinner.com/RegExr/ to test on the fly.

Answer 1

You can use following regex:

(?:{.*?)?{|}}?

This makes all the content outside the inner braces optional.

(?:{.*?)?   // Contents before the opening inner brace '{' (Optional)
 {   
   |
 }
}?          // Last brace (Optional)

See demo on http://regexr.com?35t3r

Answer 2

那例如

/{(123{)?/

Answer 3

Try using this code:

Pattern pattern = Pattern.compile("\\{(.*\\{|[^\\}]*)");
        Matcher matcher1 = pattern.matcher("{123{a,b}}");
        Matcher matcher2 = pattern.matcher("{a,b}");

        while (matcher1.find()) {
            System.out.println(matcher1.group());
        }
        while (matcher2.find()) {
            System.out.println(matcher2.group());
        }

Output:
{123{
{a,b