How do I obtain annotations at runtime using reflection?

This example demonstrate how to obtain annotations of a class and methods. We use the reflection API to get class and method information from where we can read information about annotation attached to the class or the method.

package org.kodejava.lang.annotation;

import java.lang.annotation.Annotation;
import java.lang.reflect.Method;

@HelloAnnotation(value = "Hello", greetTo = "Universe")
public class GettingAnnotation {
    public static void main(String[] args) {
        GettingAnnotation demo = new GettingAnnotation();

        Class<? extends GettingAnnotation> clazz = demo.getClass();
        Annotation[] annotations = clazz.getAnnotations();
        for (Annotation annotation : annotations) {
            System.out.println("Annotation Type: " + annotation.annotationType());
        }

        HelloAnnotation annotation = clazz.getAnnotation(HelloAnnotation.class);
        System.out.println("Value  : " + annotation.value());
        System.out.println("GreetTo: " + annotation.greetTo());

        try {
            Method m = clazz.getMethod("sayHi");

            annotation = m.getAnnotation(HelloAnnotation.class);
            System.out.println("Value  : " + annotation.value());
            System.out.println("GreetTo: " + annotation.greetTo());
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }

        demo.sayHello();
    }

    @HelloAnnotation(value = "Hi", greetTo = "Alice")
    public void sayHi() {
    }

    @HelloAnnotation(value = "Hello", greetTo = "Bob")
    public void sayHello() {
        try {
            Method method = getClass().getMethod("sayHello");
            HelloAnnotation annotation = method.getAnnotation(HelloAnnotation.class);

            System.out.println(annotation.value() + " " + annotation.greetTo());
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
    }
}

You can find the HelloAnnotation annotation that we use above on the following example: How do I create a simple annotation?.

The result of our program is:

Annotation Type: interface org.kodejava.lang.annotation.HelloAnnotation
Value  : Hello
GreetTo: Universe
Value  : Hi
GreetTo: Alice
Hello Bob

Author
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Wayan

Founder at Kode Java

A Java programmer who lives on the island of Bali, Indonesia. Programming in Spring Framework, Hibernate / JPA, MySQL. To support me working on this project, buy me a cup of coffee, every little bit helps. Thank you.

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