NullPointerException behavior on using Annotations

Question

EDIT (Show the real problem instead of a sample code Annotation code)

I created my own way of loading fxml files in Javafx 8 by using Annotation instead of using the fx:controller tag using this blog, Designing JavaFX Business Applications

I came up with this idea for dealing with Javafx fxml files.

@Target(value = {ElementType.TYPE, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface FXMLConfig {

    public String path();

}

So if I have a Javafx controller SampleController , it would look like this

@FXMLConfig(path = "/path/to/SampleController.fxml")
public class SampleController implements Initializable { ... }

To load the GUI I used a class named JavafxWindow

public class JavafxWindow {

    private Stage stage;
    private Scene scene;
    private FXMLLoader loader;

    public void setup(Object controller) throws IOException {
        FXMLConfig config = controller.getClass().getAnnotation(FXMLConfig.class);
        this.loader = new FXMLLoader(controller.getClass().getClassLoader().getResource(config.path()));
        this.loader.setController(controller);
        Parent parent = (Parent) loader.load();
        this.scene = new Scene(parent);
        this.stage = new Stage();
    }

    public void show() {
        this.stage.show();
    }

}

Now the java.lang.NullPointerException lies with in the lines

FXMLConfig config = controller.getClass().getAnnotation(FXMLConfig.class);
this.loader = new FXMLLoader(controller.getClass().getClassLoader().getResource(config.path()));

I tested the code and it worked fine but NPE behavior occurs in the production which is a very annoying bug to users. Exception is thrown at getAnnotation() or config.path() at times of heavy usage. But the production code is deployed using OSGi , Apache Felix 4.6.0 across multiple bundles . I am also using Reflection on other parts but no NPE is thrown.

Can you give me an implementation that comes with a level of checking to remove the abnormal java.lang.NullPointerException behavior?

• java version "1.8.0_45"
• Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
• Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)
• Apache Felix 4.6.0
• Ubuntu 14.04 / Windows 7 / Windows 8 / Windows 8.1

Thanks for the community's positive response.

Answer 1

Here is aa Minimal Complete Verifiable example. I haven't seen NPE of such type, so I'll post here the exact same way I always create my custom annotation for reference. Further questions welcome.

Custom Annotation Class(interface)

import java.lang.annotation.*;
@Inherited
@Documented
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)

@interface BasicBenefits {
    String bId() default "B-101";
    String bName() default "General Class A Employee";
}

Class using the custom annotation(no need of any imports):

@BasicBenefits(bId="B-400", bName="General Plus Class A Employee")
public class Employee {
    String eId;
    String eName;
    public Employee(String eId, String eName){
        this.eId = eId;
        this.eName = eName;
    }

    public void getEmployeeDetails(){
        System.out.println("Employee ID: "+eId);
        System.out.println("Employee Name: "+eName);
    }
}

Driver class to test out the above.

import java.lang.annotation.Annotation;
public class TestCustomAnnotationBasicBenefits {
    public static void main(String[] args) throws Exception{
        Employee emp = new Employee("E-100", "user3320018");
        emp.getEmployeeDetails();
        Class reflectedClass = emp.getClass();
        Annotation hopeBenefitAnn = reflectedClass.getAnnotation(BasicBenefits.class);
        BasicBenefits bBenefits = (BasicBenefits)hopeBenefitAnn;
        System.out.println("Benefit ID: "+bBenefits.bId());
        System.out.println("Benefit Name: "+bBenefits.bName());
    }
}