Finding all classes implementing a specific interface

Question

I am in the process of developing an application (Quartz scheduler) where we have a job class which is responsible for actually executing the work and we need to tell/pass the name of the job class while creating a trigger in the Quartz scheduler.

I want to provide an extension point to all who want to use the API (beside the some generic jobs which I will provide as part of the API). The idea is to create an (marker) interface and if any one wants to declare their class as scheduler job class, all they have to do is, to (declare to) implement the interface.

I am not sure how I can find which classes are following the contract (by implementing the interface) so that I can show them to the user who want to schedule a trigger in the scheduler.

My requirement is not to load the classes at run time but to show user list of classes which implement the required interface so that user can select the class and class name can be passed to the scheduler. It's the Quartz scheduler which at the end will be responsible to create an instance of class.

Can any one suggest how I can achieve the above goal or is there any other better way to achieve what I am trying to do?

Edit

I went through the doc of ServiceLoader and it seems that for implementing a service one has to create a file in the META-INF folder with the name of the implementation class, which leads me to think that if the user of my API wants 20 different implementations, he has to put 20 entries in the file which for me seems a lot of extra work for the end user since each job class will be created for executing a specific job and there can be 100s of job classes.

Please correct me if my assumption is wrong.

Answer 1

You can find an answer here.

I can suggest using org.reflections

enter link description here

Reflections reflections = new Reflections("com.mycompany");    
Set<Class<? extends MyInterface>> classes = reflections.getSubTypesOf(MyInterface.class);