Obtaining annotations at runtime using reflection

You can use getAnnotation method on Class of object, which has annotation attached to it.

Defining an annotation

package com.vaani.annotations;
 
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

    @Retention(RetentionPolicy.RUNTIME)
    public @interface HelloAnno {
    String value();
    String greetTo();
 }

 

Using the annotations

Note that I have kept value as German words, corresponding to greetTo which is in english lanaguage.

@HelloAnno(value = "Gooten Morgen", greetTo = "GoodMorning")
public class AnnotationUser{  
  @HelloAnno(value = "Gooten Tag", greetTo = "Hi")
    public void sayHi() {
    }
//
    @HelloAnno(value = "Gute Nacht", greetTo = "GoodNight")
    public void sayHello() {
    try {
        Method m = getClass().getMethod("sayHello");
        HelloAnno anno = m.getAnnotation(HelloAnno.class);
     
        System.out.println(anno.value() + " " + anno.greetTo());
      } catch (NoSuchMethodException e) {
        e.printStackTrace();
      }
     }
}

 

Method to print all annotation

public static void printAnnotations(Class clazz){
    Class clazz = demo.getClass();
    Annotation[] annotations = clazz.getAnnotations();
    for (Annotation anno : annotations) {
       System.out.println("Annotation Type: " + anno.annotationType());
//Prints Annotation Type: interface com.vaani.annotations

    }
 
    HelloAnno anno = (HelloAnno) clazz.getAnnotation(HelloAnno.class);
    System.out.println("Anno Value  : " + anno.value());
    System.out.println("Anno GreetTo: " + anno.greetTo());
//Outputs
Anno value : Gooten Morgen
Anno GreetTo : GoodMorning

    try {
        Method m = clazz.getMethod("sayHi");
     
        anno = m.getAnnotation(HelloAnno.class);
        System.out.println("Anno Value  : " + anno.value());
        System.out.println("Anno GreetTo: " + anno.greetTo());
 
//Outputs
Anno value : Gooten Tag
Anno GreetTo : Hi


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

Runner or tester class to show annotation:

public static void main(String[] args) {
    GettingAnnotation demo = new GettingAnnotation();
    Class clazz = demo.getClass();
    printAnnotation(clazz);
}