How to access package level annotations in package-info.java runtime from a jar?

Question

How can i access all package-info classes in a jar in my class path ? I want to access the package level annotations used in these classes.

I want to do the following steps:-

1. Find all the package-info.java classes
2. Get their packages
3. Get the annotation @PackageOwner

Answer 1

There's a more simple solution, not involving an external api. You can get the Package object from a class located in the package for which you want the annotations. And then get these annotations by calling the method getAnnotations() on the package :

import java.lang.annotation.Annotation;

public class PackageAnnotationsTest {

    public static void main(String[] args) {
        Package myPackage = AClassInMyPackage.class.getPackage();
        Annotation[] myPackageAnnotations = myPackage.getAnnotations();
        System.out.println("Available annotations for package : " + myPackage.getName());
        for(Annotation a : myPackageAnnotations) {
            System.out.println("\t * " + a.annotationType());
        }
    }
}

Thanks to this link that helped me on this question. I had first read this thread and Parikshit's answer but I didn't want to use an external api.

Answer 2

guava 14+ came to the rescue :)

following code works

public class OwnerFinder {
    public static void main(String[] args) {
        try {
            ClassPath classPath = ClassPath.from(OwnerFinder.class.getClassLoader());
            classPath.getTopLevelClassesRecursive("com.somepackage")
                    .stream()
                    .filter(c -> c.getSimpleName().equals("package-info"))
                    .map(c -> c.load().getPackage().getAnnotation(PackageOwner.class))
                    .forEach(a -> System.out.println(a.owner()));

        } catch(IOException e) {
            e.printStackTrace();
        }
    }
}

application of the annotation is below for the package-info.java

@PackageOwner(owner = "shaikhm")
package com.somepackage;