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Java / MapStruct Java Interview questions part 2

Why is MapStruct faster than reflection-based mapping libraries?

Reflection-based mappers look up fields, getters, and setters through java.lang.reflect on every mapping call. Reflective invocation carries overhead for access checks, method lookup, and boxing/unboxing, which adds up under heavy load.

MapStruct avoids all of that because the mapping decisions - which getter feeds which setter, which types need conversion - are resolved once, during compilation. The generated class contains ordinary method calls like target.setName(source.getName()), so at runtime the JVM executes it exactly like hand-written code, including normal JIT optimization.

The result is that a MapStruct-generated mapper typically performs within a small margin of manually written mapping code, whereas reflection-based approaches carry a measurable and consistent per-call cost.

Reflection-based mapping adds overhead mainly because of:
MapStruct's generated code executes fields as:

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