How can I introspect a freemarker template to find out what variables it uses?

Question

I\'m not at all sure that this is even a solvable problem, but supposing that I have a freemarker template, I\'d like to be able to ask the template what variables it uses.<

Answer 1

I solved this for my very simple usecase (only using flat datastructure, no nesting (for example: ${parent.child}), lists or more specific) with dummy data provider:

public class DummyDataProvider extends HashMap {
    private static final long serialVersionUID = 1;

    public final Set variables = new HashSet<>();

    @SuppressWarnings("unchecked")
    @Override
    public V get(Object key) {
        variables.add(key.toString());
        return (V) key;
    }
}

You can give this for processing to a template and when it finishes Set variables contains your variables.

This is very simplistic approach, which certainly needs improvement, but you get the idea.