Validating Template Against JSON

I'm trying to validate a template given a JSON structure.  By this I mean,
given a template with fields to read from a JSON file, and the JSON file,
I'd like to ensure all of the fields expected in the template are present in
the JSON file.  A programmatic version of this would be perfect (with an
error message, rather than an empty template if the JSON property doesn't
exist):

https://try.freemarker.apache.org/


Is there an existing solution to this, or is this something I'll have to
write myself?  If it is something I'll have to write myself, and suggestions
on how to proceed with this task?



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