java-core-examples/annotation-processor/README.md

annotation-processor

Companion code for the ankurm.com post "Custom Annotations and Annotation Processors in Java: Generate Code at Compile Time." A module of java-core-examples; itself a small two-module Maven build.

Versions this was built and tested against

Component	Version
JDK	25.0.5+8 (Temurin, LTS)
Maven	3.9.11
maven-compiler-plugin	3.16.0
maven-surefire-plugin	3.6.1
JUnit Jupiter	6.1.3

Run it

export JAVA_HOME=/path/to/jdk-25
mvn -B clean test          # from this directory: builds the processor, then the demo that uses it
scripts/run-all.sh         # also regenerates every file in output/

Files

Path	What it is
processor/.../GenerateBuilder.java	The annotation (SOURCE retention, TYPE target, two members with defaults)
processor/.../BuilderProcessor.java	The AbstractProcessor that writes <Type>Builder through Filer, reports problems through Messager
processor/src/main/resources/META-INF/services/javax.annotation.processing.Processor	Registration
processor/src/test/.../Compilation.java, ProcessorCompileTest.java	In-memory javax.tools.JavaCompiler harness and its tests (writes output/09)
demo/.../Person.java, Pizza.java	Consumers of @GenerateBuilder (a record and a class)
demo/.../annotations/*	SOURCE / CLASS / RUNTIME annotations, @Inherited, @Repeatable, members and defaults
demo/.../RetentionDemo.java, RuntimeValidatorDemo.java	What reflection sees; a reflection-based validator
demo/src/test/...	Runtime tests of the generated builders and of the reflection behaviour
bad/Shape.java	Deliberately invalid input for the compile-error transcript
output/01..10	Captured runs; the post quotes these verbatim

demo/pom.xml has two throwaway profiles (classpath-only, classpath-proc-full) used only to capture output/08.