maven插件处理接口注解

Question

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;

Answer 1

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