Apache Velocity : Verify if all substitutions are made

Can someone let me know how I can verify a velocity context against a template? Basically, I want to throw some error if all variables are not substituted in the velocity template.

For example, let's say I have a velocity template, card.vm

  card {
    type: CREDIT
    company: VISA
    name: "${firstName} ${lastName}"
  }

The substitution is done like below

VelocityEngine velocityEngine = new VelocityEngine();
velocityEngine.init();
   
Template t = velocityEngine.getTemplate("card.vm");
    
VelocityContext context = new VelocityContext();
context.put("firstName", "tuk");
StringWriter writer = new StringWriter();
t.merge( context, writer );

In this case, I want to throw some error specifying that lastName is not replaced in template.

Does velocity provide anything for this?

• Velocity Version - 1.7

This has been answered in velocity mailing list

> No, but it would be easy to do. Instead of using the basic
> VelocityContext, wrap it in a custom one, something like this:
>
> public class WarningVelocityContext
> extends VelocityContext
> {
> public Object get(String key) {
> Object o = super.get(key);
>
> if(null == o) {
> throw new IllegalStateException("Key {" + key + "} has not
> been set");
> }
> }
> }
>
> Then in your code, wrap the context right before merging:
>
> t.merge(new WarningVelocityContext(context), writer);
>
> Note that this will throw exceptions for anything that's not found
> for any reason. If you try something like:
>
> $someObject.method()
>
> And "someObject" is null, then you'll get an error. It may be
> difficult to tell the difference between the things you "care about"
> and the things you do not. If you have a simple use-case, then
> probably this will work.