How to read file from src/main/resources with annotation processor?

Question

I have a simple annotation processor that needs to read a configuration file from the same project as the annotated classes. Example structure:

- myproject 
  - src
    - main
      - java
        - my.package.SourceFile
      - resources
        - config.json

In the annotation processor, I try to read the file:

FileObject resource = processingEnv.getFiler().getResource(StandardLocation.SOURCE_PATH, "", "config.json");

but it throws FileNotFoundException . I also tried other paths, such as ../resources/config.json , (which throws Invalid relative name: ../resources/config.json ). And I tried putting the config file in src/main/java (and even src/main/java/my/package ) instead, which I don't like, but that also still throws FileNotFoundException .

It would already help if I could get filer.getResource() to tell me where it's looking. To find that out, I tried generating a file:

filer.createResource(StandardLocation.SOURCE_OUTPUT, "", "dummy");

which generated in myproject/build/classes/main/dummy . Unfortunately, I can't generate in SOURCE_PATH , so that doesn't help with finding this out.

Answer 1

I'd expect that the stuff from src/main/resources gets copied to target/classes during the build (prior to annotation processing). In that case you can open them like this:

ProcessingEnvironment pe = ...;
FileObject fileObject = pe.getFiler()
    .getResource( StandardLocation.CLASS_OUTPUT, "", "config.json" );
InputStream jsonStream = fileObject.openInputStream();

Answer 2

I've looked at this with one of the Project Lombok developers. If anyone knows annotation processing, it's them ;)

Our conclusion was, that the JavacFileManager that handles the request internally, does not have a path to resolve StandardLocation.SOURCE_PATH to. We're not sure, but it might be related to building with Gradle.

Answer 3

I had the same problem and was searching for solution for a while and found this cool hack that does the trick for Android

And below you can see my solution from pure Java/Kotlin project

fun ProcessingEnvironment.getResourcesDirectory(): File {
val dummySourceFile = filer.createSourceFile("dummy" + System.currentTimeMillis())
var dummySourceFilePath = dummySourceFile.toUri().toString()

if (dummySourceFilePath.startsWith("file:")) {
    if (!dummySourceFilePath.startsWith("file://")) {
        dummySourceFilePath = "file://" + dummySourceFilePath.substring("file:".length)
    }
} else {
    dummySourceFilePath = "file://$dummySourceFilePath"
}

val cleanURI = URI(dummySourceFilePath)

val dummyFile = File(cleanURI)

val projectRoot = dummyFile.parentFile.parentFile.parentFile.parentFile.parentFile

return File(projectRoot.absolutePath + "/resources")
}

Answer 4

Following function works for me with annotation processor being triggered by gradle, it's not the pretties one but works:

private fun resolveApplicationPropertiesFile(): File {
    val projectRoot = Path.of(processingEnv.filer.getResource(StandardLocation.CLASS_OUTPUT, "", "doesntmatter")
            .toUri())
            .parent
            .parent
            .parent
            .parent
            .parent
            .parent
    val properties = Path.of(projectRoot.toString(), "src", "main", "resources", "application.yml")
    return properties.toFile()
}

where processingEnv is a member of AbstractProcessor

Answer 5

• If your element is instance of TypeElement ,then you can use these code to find your source code

  FileObject fileObject = processingEnv.getFiler().getResource( StandardLocation.SOURCE_PATH, element.getEnclosingElement().toString(), element.getSimpleName() + ".java");

  1. element.getEnclosingElement() is your class package, eg: com.fool
  2. element.getSimpleName() is your class name, eg: Person

• then you can print them: CharSequence content = fileObject.getCharContent(true);