Question

I am using Reflections to obtain a method from a class that is annotated with a specific annotation. Once I get the list of methods in the class, I loop through the methods and if the method matches a specific return type, I want to invoke that method. For testing purposes I know that the method I am getting returns a String.

Reflections reflections = new Reflections(new ConfigurationBuilder()
        .setScanners(new TypesScanner(), new TypeElementsScanner())
        .setUrls(ClasspathHelper.forPackage("stressball"))
);

Set<Class<?>> annotated = reflections.getTypesAnnotatedWith(DependantClass.class);
System.out.println(annotated);

for(Class<?> clazz : annotated) {
    for(Method method : clazz.getMethods()) {
        if(method.isAnnotationPresent(DependantResource.class)) {
            if(method.getReturnType() == String.class) {
                System.out.println(method.invoke(method,(Object[]) null));
            }                   
        }
    }
}

This is the method I am attempting to invoke

@DependantResource
public String showInjector() {
    return "This is an injector";
}

I keep getting the following error and I know it has everything to do with the object I am passing into invoke, but is the method from the loop not the object I am supposed to be passing?

Exception in thread "main" java.lang.IllegalArgumentException: object is not an instance of declaring class
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at stressball.test.DefaultTest.main(DefaultTest.java:35)

Answer 1

This is not correct:

method.invoke(method,(Object[]) null)

You should instantiate an object first, and then make a call. Something like:

method.invoke(clazz.newInstance(), (Object[]) null)