Question

I’m looking for a Java class that for a given string “the ${animal} jumped over the ${target}.” is able to pull out the variable names, ie ‘animal’ and ‘target’.

I had hoped StrSubstitutor in Commons Lang had a method
getVariables(String str) : List<String>
… but no such luck.

Yes I could write this myself, but I’m certain there must be a 3rd party library that exists out there that does this.

Answer 1

You could just do a simple regex match if you really just want to pull out those values and avoid the dependency of an entire library:

public List<String> getVariableNames(String source) {
  List<String> vs = new ArrayList<String>();
  Pattern p = Pattern.compile("\\$\\{(\\w+)\\}");
  Matcher m = p.matcher(source);
  while (m.find()) {
    vs.add(m.group(1));
  }
  return vs;
}

Storing the pattern as a member variable will improve performance.