JAVA EE: How to access the method Annotation using Java Reflection

Tuesday, 7 November 2017

How to access the method Annotation using Java Reflection | Reflection in java

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https://www.youtube.com/watch?v=_9EQcNFq47E&list=UUhwKlOVR041tngjerWxVccw

Display.java

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)

@interface MyAnnotation
{
    public String name();

    public String value();
}

public class Display
{
    @MyAnnotation(name = "Country", value = "India")
    public void doSomething()
    {
    }
}

ReflectionDemo1.java

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

/**
 * We can access the annotations of a class,method or field at runtime.
 * 
 * Method Annotations Example:
 */
public class ReflectionDemo1
{
    public static void main(String[] args)
    {
        try
        {
            Class<Display> classObj = Display.class;
            Method method = classObj.getMethod("doSomething", null);
            /*
             * Returns:annotations present on this element           * 
             */
            Annotation[] annotationArray = method.getAnnotations();
            
            for (Annotation annotation : annotationArray)
            {
                if(annotation instanceof MyAnnotation)
                {
                    MyAnnotation myAnnotation = (MyAnnotation)annotation;
                    System.out.println("name: "+myAnnotation.name());
                    System.out.println("value: "+myAnnotation.value());
                }
            }
        }
        catch (NoSuchMethodException | SecurityException e)
        {
            e.printStackTrace();
        }
    }

}

Output

name: Country
value: India

ReflectionDemo2.java

import java.lang.reflect.Method;

/**
 * We can access the annotations of a class,method or field at
 * runtime.
 * 
 * Method Annotations Example:
 */
public class ReflectionDemo2
{
    public static void main(String[] args)
    {
        try
        {
            Class<Display> classObj = Display.class;
            Method method = classObj.getMethod("doSomething", null);
            /*
             * Returns: this element's annotation for the specified
             * annotation type if present on this element, else null
             * 
             */
            MyAnnotation myAnnotation = method.getAnnotation(MyAnnotation.class);
            System.out.println("name: " + myAnnotation.name());
            System.out.println("value: " + myAnnotation.value());

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

}