Snippet to get classes belonging to a package at runtime that have a certain annotation

TestRuntimeInitializationOfChain.java

 package org.wikimedia.analytics.refinery.tag;

import com.google.common.collect.ImmutableSet;
import com.google.common.reflect.ClassPath;

import java.util.ArrayList;
import java.util.List;
import java.util.Set;

import org.reflections.*;

import java.util.Iterator;

public class TagChain {

    List<String>  tags = new ArrayList<String>();

    List<Tagger>  chain = new ArrayList<Tagger>();


    public TagChain() throws Exception {

        // now get all classes that are part of this chain
        // scan annotations at runtime and build it
        // or get it from package

        ClassLoader loader = this.getClass().getClassLoader();
        ClassPath p = ClassPath.from(loader);




        ImmutableSet<ClassPath.ClassInfo> listOfClasses =
            p.getTopLevelClasses("org.wikimedia.analytics.refinery.tag.impl");


        for( ClassPath.ClassInfo ci:listOfClasses) {
            Class<?> clazz = Class.forName(ci.getName()) ;


            chain.add((Tagger) clazz.newInstance());
        }

        Reflections reflections  = new Reflections("org.wikimedia.analytics.refinery.tag.impl");
        Set<Class<?>> taggerClasses = reflections.getTypesAnnotatedWith(org.wikimedia.analytics.refinery.tag.Tag.class‌​);

        System.out.println(taggerClasses);

        for(Class taggerClass:taggerClasses){
            Class<?> clazz = Class.forName(taggerClass.getName());

            System.out.println(taggerClass.getName());
            chain.add((Tagger) clazz.newInstance());


        }

    }





}