Injecting Jar Version into Java Components Using Insert Annotation Processors

The author needed to monitor the usage of internal Java component jars via Prometheus and wanted a way to automatically inject each jar's version into a constant field.

Manually updating version constants for every release is cumbersome, so the author sought a compile‑time solution similar to Lombok's annotation processing.

By defining a custom annotation @TrisceliVersion and an annotation processor that extends AbstractProcessor , the processor reads the jar version during compilation and assigns it to the annotated field by modifying the abstract syntax tree (AST).

The annotation is declared as: @Documented @Retention(RetentionPolicy.SOURCE) @Target({ElementType.FIELD}) public @interface TrisceliVersion {} The processor implements initialization, supported annotations, and the process method where it locates fields annotated with @TrisceliVersion , checks that they are of type String , and sets their initializer to the value returned by getVersion() (stubbed to return "v1.0.1").

Registration of the processor is done via the SPI mechanism by adding its fully‑qualified name to META-INF/services/javax.annotation.processing.Processor .

For testing, a new Gradle module imports the processor, builds the project, and the resulting bytecode shows the version field populated with the injected value.

The author concludes that insert annotation processors enable powerful compile‑time code generation, allowing developers to create plugins beyond Lombok and automate repetitive tasks such as version injection.