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 had the same problem and none of posted solution made sense to me. What I came with is plugging custom implementation of TemplateExceptionHandler. Example:

final private List<String> missingReferences = Lists.newArrayList();
final Configuration cfg = new Configuration(Configuration.VERSION_2_3_23);
cfg.setTemplateExceptionHandler(new TemplateExceptionHandler() {

    @Override
    public void handleTemplateException(TemplateException arg0, Environment arg1, Writer arg2) throws TemplateException {
        if (arg0 instanceof InvalidReferenceException) {
            missingReferences.add(arg0.getBlamedExpressionString());
            return;
        }
        throw arg0;
    }

}

Template template = loadTemplate(cfg, templateId, templateText);

StringWriter out = new StringWriter();

try {
    template.process(templateData, out);
} catch (TemplateException | IOException e) {
        throw new RuntimeException("oops", e);
}

System.out.println("Missing references: " + missingReferences);

Read more here: https://freemarker.apache.org/docs/pgui_config_errorhandling.html