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

Tuesday, 7 November 2017

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

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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.FIELD)

@interface MyAnnotation
{
    public String name();

    public String value();
}

public class Display
{

    @MyAnnotation(name = "age", value = "25")
    public String myField = null;
}

ReflectionDemo1.java

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

/**
 * Example of a field with annotations
 */
public class ReflectionDemo1
{
    public static void main(String[] args)
    {
        try
        {
            Class<Display> classObj = Display.class;
            Field field = classObj.getField("myField");
            Annotation[] annotations = field.getDeclaredAnnotations();

            for (Annotation annotation : annotations)
            {
                if (annotation instanceof MyAnnotation)
                {
                    MyAnnotation myAnnotation = (MyAnnotation) annotation;
                    System.out.println("name: " + myAnnotation.name());
                    System.out.println("value: " + myAnnotation.value());
                }
            }
        }
        catch (NoSuchFieldException | SecurityException e)
        {
            e.printStackTrace();
        }

    }

}

ReflectionDemo2

import java.lang.reflect.Field;

/**
 * Example of a field with annotations
 */
public class ReflectionDemo2
{
    public static void main(String[] args)
    {
        try
        {
            Class<Display> classObj = Display.class;
            Field field = classObj.getField("myField");
            MyAnnotation myAnnotation = field.getAnnotation(MyAnnotation.class);

            System.out.println("name: " + myAnnotation.name());
            System.out.println("value: " + myAnnotation.value());
        }
        catch (NoSuchFieldException | SecurityException e)
        {
            e.printStackTrace();
        }

    }

}