Java Annotation processor for remote JAR

Question

General question

I have two projects A and B; B has a dependency on A. I want to generate some code in B with an Annotation Processor, based on annotations on objects in A. When I run the compilation with the correct Processor implementation, only the annotated objects from B are picked up.

I understand that scanning other JARs must be disabled by default, because you usually don't want to do an annotation scan for all your dependencies. I also understand that it may be impossible to do what I want to do because of compiler magic - which I don't know a lot about - but I'm hoping it's not.

Specific case

My projects are called DB and WEB. WEB obviously depends on DB for its JPA access; this is configured in Maven. Due to a number of architectural choices, DB must remain a separate JAR. DB doesn't use Spring except for some annotations which are consumed by WEB; WEB uses Spring MVC.

I'm trying to generate the CrudRepository interfaces for all my JPA entities with an Annotation Processor. The @Repository objects are supposed to go in a repo package in the WEB project, so they can be used with @Autowired wherever in my WEB application. The annotation I'm performing the scan for is @javax.persistence.Entity, but I've also tried a custom annotation, with the same results.

@SupportedAnnotationTypes("javax.persistence.Entity")
@SupportedSourceVersion(SourceVersion.RELEASE_8)
public class RepositoryFactory extends AbstractProcessor {

    @Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
        for (Element e : roundEnv.getElementsAnnotatedWith(Entity.class)) {
            if (e.getKind() != ElementKind.CLASS) {
                continue;
            }
            // TODO: implement logic to skip manually implemented Repos
            try {
                String name = e.getSimpleName().toString();
                TypeElement clazz = (TypeElement) e;

                JavaFileObject f = processingEnv.getFiler().
                        createSourceFile("blagae.web.repo." + name + "Repo");
                try (Writer w = f.openWriter()) {
                    PrintWriter pw = new PrintWriter(w);
                    pw.println("package blagae.web.repo;");
                    pw.println("import org.springframework.data.repository.CrudRepository;");
                    pw.printf("import %s;\n", clazz.toString());
                    pw.println("import org.springframework.stereotype.Repository;");
                    pw.println("@Repository");
                    pw.printf("public interface %sRepo extends CrudRepository<%s, Long> {}\n", name, name);
                    pw.flush();
                }
            } catch (IOException ex) {
                Logger.getLogger(RepositoryFactory.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
        return false;
    }
}

Ideally, I'd love for someone to tell me about an annotation that would be as simple as

@ComponentScan(basePackages = "blagae.db.*")

But of course, I'm not counting on that because it would probably be documented somewhere. As a workaround, I could just add the Spring dependency to the db and generate the classes there, but they only serve a purpose in the Spring MVC app. I'm also wary of the config it might take to make this work.

UPDATE

Some extra info: I'm using the maven-processor-plugin, which I've verified to work well in the WEB project for classes that are defined there. However, I specifically want access classes annotated in the dependency project DB. I have looked into the method AbstractProcessor::getSupportedOptions but it's unclear to me what I could do there.

Maven config:

<plugin>
    <groupId>org.bsc.maven</groupId>
    <artifactId>maven-processor-plugin</artifactId>
    <version>2.2.4</version>
    <configuration>
        <processors>
            <processor>blagae.utils.RepositoryFactory</processor>
        </processors>
    </configuration>
    <executions>
        <execution>
            <id>process</id>
            <goals>
                <goal>process</goal>
            </goals>
            <phase>generate-sources</phase>
        </execution>
    </executions>
</plugin>

SUGGESTION

Another random thought I had would be to run a JavaCompiler process for the DB project in WEB, but how would I inject my Processor ?

Answer 1

Annotation processor works on compilation phase of your project (WEB in your case) and compiler compiles this project. Dependencies of current project are already compiled and compiler (and as result your annotation processor) don't touch (or have no access) third party libraries (DB).

You can try to extract annotation processor into separate project/jar and use it in WEB and DB projects. In this case annotation processor will create CrudRepository on compilation phase of concrete project. And all generated classes in DB project will be available in WEB.