How to get the class code as String from Annotation Processor?

Question

I have a basic Annotation Processor

@SupportedAnnotationTypes("example.Annotation")
public class Processor extends AbstractProcessor {
    @Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
        for (TypeElement annotation : annotations) {
            Set<? extends Element> elementsAnnotatedWith = roundEnv.getElementsAnnotatedWith(annotation);
            for (Element element : elementsAnnotatedWith) {
                TypeElement typeElement = (TypeElement) element;
                // Here, typeElement.getQualifiedName() is accessible, but not the code nor file path.
            }
        }
        return false;
    }
}

This annotation can only be used on classes. I know the target class is not compiled so reflective access is not possible but I would like to get the class code as String to parse in my own way instead of using this API.

Is it possible? I know I can get qualified name but where to look for the file?

Do you really need the complete source code, or reflection informations (method signatures, field declaration, inheritance, ...) is enough ? — Tigger
– Tigger, Commented May 8, 2021 at 14:30
@Tigger I already hade a lot of code based on parsing class code so I wanted to re-use it. But there seems to be no way so I had to rewrite my code using this API (processingEnv.getElementUtils()). — Nand
– Nand, Commented May 8, 2021 at 17:36
Actually, I still need the other method. For copying a method from the annotated class to the generated class... — Nand
– Nand, Commented May 8, 2021 at 17:46
Since it happens before compilation, all the source files you need have to be there, somewhere on the file system, right ? If so, I bet there is some environment variable you could use. How do you compile/build your library (maven, gradle, ...) ? — Tigger
– Tigger, Commented May 8, 2021 at 17:54
I use Gradle but won't that make the annotation processor only work for me? — Nand
– Nand, Commented May 8, 2021 at 18:11

Tigger · Accepted Answer · 2021-05-23 01:39:44Z

2

The source code of a TypeElement can be loaded like this:

private String loadSource(TypeElement typeElement) throws IOException {
    final FileObject source = processingEnv.getFiler().getResource(
        StandardLocation.SOURCE_PATH,
        ((PackageElement) typeElement.getEnclosingElement()).getQualifiedName(),
        typeElement.getSimpleName() + ".java");
    
    try (Reader reader = source.openReader(true)) {
        final StringBuilder builder = new StringBuilder();
        final char[] buf = new char[1024];
        int read;
        while ((read = reader.read(buf)) != -1) {
            builder.append(buf, 0, read);
        }
        return builder.toString();
    }
}

The tested Processor jar contains a META-INF/services/javax.annotation.processing.Processor file, no need to specify -process option:

Maven : OK
Gradle : extra configuration needed, assuming src/main/java is the source directory

tasks.withType(JavaCompile) {
    configure(options) {
        options.setSourcepath(project.files('src/main/java'))
    }
}

Command line: add -sourcepath option:

javac -cp path/to/processor.jar -sourcepath path/to/sources path/to/JavaFile.java

edited May 23, 2021 at 1:39

answered May 9, 2021 at 18:38

Tigger

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2 Comments

Nand Over a year ago

Unfortunately SOURCE_PATH is null in Gradle :(

Tigger Over a year ago

I found a way to make it work with Gradle, and updated my answer. I hope it will work for you.

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