Question

What would be a convenient and reliable way to extract all the “{…}” tags from a given string? (Using Java).

So, to give an example:
Say I have: http://www.something.com/{tag1}/path/{tag2}/else/{tag3}.html

I want to get all the “{}” tags; I was thinking about using the Java .split() functions, but not sure what the correct regex would be for this.

Note also: tags can be called anything, not just tagX!

Answer 1

I would use regular expressions to match this. Something like this could work for your expression:

String regex = "\\{.*?\\}";

As this will “reluctantly” match any sub string that has { and } surrounding it. The .*? makes it find any character between the { and }, but reluctantly, so it doesn’t match the bigger String:

{tag1}/path/{tag2}/else/{tag3}

which would be a “greedy” match. Note that the curly braces in the regex need to be escaped with double backslashes since curly braces have a separate meaning inside a regular expression, and if you want to indicate the curly brace String, you need to escape it.

e.g.,

   public static void main(String[] args) {
      String test = "http://www.something.com/{tag1}/path/{tag2}/else/{tag3}.html";
      String regex = "\\{.*?\\}";

      Pattern pattern = Pattern.compile(regex);
      Matcher matcher = pattern.matcher(test);

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

With an output of:

{tag1}
{tag2}
{tag3}

You can read more about regular expressions here:
Oracle Regular Expressions Tutorial

and for greater detail, here:
http://www.regular-expressions.info/tutorial