[FIXED] Processing interface annotations by maven plugin

Issue

I have an annotation-processor java app that is looking into the target folder of the external maven project for the class files. This app uses URLClassLoader. The target folder is the absolute path app parameter. I have a simple junit test which is loading classes and processing the annotations successfully. Now I wrote the maven plugin that is just a wrapper for annotation-processor app. When running this maven plugin, annotation-processor loads the classes but it does not see any annotations in those. How can I access class/interface annotations from the maven plugin?

• maven-plugin-plugin:3.6.4
• java 11.0.15

    private static Class<?> getClass(String path, String className, String packageName) {
        File file = new File(path);
        try {
            URL[] urls = new URL[]{file.toURI().toURL()};
            ClassLoader cl = new URLClassLoader(urls);
        return cl.loadClass(packageName + "." + className));
        } catch (MalformedURLException | ClassNotFoundException e) {
            log.warn("Cannot find class: " + packageName + "." + className, e);
        }
        return null;
    }

Example call:

Class clazz = getClass("/home/user/java/my-project/target/classes", "MyClass", "com.my.example.package");
assert clazz.getAnnotations() > 0;

Solution

There are two possible reasons:

1. your annotations do not have proper @Retention
2. JVM silently drops information about annotations while loading the class - that may happen if classloader does know nothing about annotation classes - that is very likely your case because you are instantiating new classloader without specifying parent

Answered By - Andrey B. Panfilov
Answer Checked By - Willingham (JavaFixing Volunteer)