List variables from freemarker file

freemarker_listVariables

// implementation-dependant (freemarker 2.3.14)
private List<String> getTemplateVariables(Template freemarkerTemplate) throws IOException, TemplateModelException {
    SimpleSequence childNodes = (SimpleSequence) freemarkerTemplate.getRootTreeNode().getChildNodes();
    List<String> dollarVariables = new ArrayList<String>();
    for (Object object : childNodes.toList()) {
        if (object instanceof TemplateElement && ((TemplateElement) object).getCanonicalForm().startsWith("$")) {
            dollarVariables.add(((TemplateElement) object).getCanonicalForm());
        }
    }
    return dollarVariables;
}