API / Apache FreeMarker Interview questions

What happens when a variable referenced in a template is not found in the data model?

Referencing an undefined variable and then trying to actually use it - printing it, comparing it, calling a method on it - raises an InvalidReferenceException, a subtype of TemplateException, which by default aborts processing of that template.

What happens next depends on the TemplateExceptionHandler configured on the Configuration:

Handler	Behavior
RETHROW_HANDLER	Propagates the exception out of process(); recommended for production so the caller can log it and show an error page
DEBUG_HANDLER	Prints a stack trace and FTL context into the output stream; useful only in development
HTML_DEBUG_HANDLER	Same as DEBUG_HANDLER but HTML-formatted
IGNORE_HANDLER	Swallows the error and continues; risky, since it can silently hide bugs

Guarding the reference with ?? or supplying a default with ! avoids triggering the exception in the first place, which is the normal way to handle genuinely optional data.

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What exception type is raised when an undefined variable is actually used in the output?A plain Java NullPointerException

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InvalidReferenceException, a subtype of TemplateException

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IOException

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ParseException

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Which TemplateExceptionHandler is recommended for a production application?HTML_DEBUG_HANDLER

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RETHROW_HANDLER

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IGNORE_HANDLER

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DEBUG_HANDLER

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What is the purpose of interpolation (${...}) in FreeMarker? List the comparison operators supported in FreeMarker? What are the main use cases of FreeMarker? What are the types in FreeMarker's data model? How do you use the #assign directive? Describe the built-ins available in FreeMarker? How do you access static Java members (static methods, fields, and enum constants) from a FreeMarker template? What is Apache FreeMarker? What is the purpose of the FreeMarker Configuration object? What is the difference between FreeMarker's #switch/#case and a chain of #if/#elseif directives? What is the purpose of the <#if> directive? What are the types of loops available in FreeMarker? What is the difference between #assign and #local? How do you apply default values for missing variables in FreeMarker? Why doesn't FreeMarker allow templates unrestricted access to Java reflection and side-effecting method calls? What is the purpose of the incompatible_improvements setting? Define directive in FreeMarker? Which is generally the better choice for a new project today, FreeMarker or Velocity, and why? What is a FreeMarker template? What is the purpose of the #include directive?

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