Java - Accessing Annotations at Runtime

Introduction

An annotation type must be annotated with the Retention meta-annotation with the retention policy of runtime to access it at runtime.

The access to annotation type is via AnnotatedElement interface.

The following classes implement the AnnotatedElement interface:

java.lang.Class
java.lang.reflect.Executable
java.lang.reflect.Constructor
java.lang.reflect.Field
java.lang.reflect.Method
java.lang.reflect.Parameter
java.lang.Package
java.lang.reflect.AccessibleObject

Demo

import java.lang.annotation.Annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.AnnotatedElement;
import java.lang.reflect.Method;

@Target({ ElementType.TYPE, ElementType.CONSTRUCTOR, ElementType.METHOD, ElementType.PACKAGE })
@Retention(RetentionPolicy.RUNTIME)
@Documented//from   w  w  w .  j  av  a  2 s.com
@interface Version {
  int major();

  int minor();
}

@Version(major = 1, minor = 0)
class AccessAnnotation {
  @Version(major = 1, minor = 1)
  public void testMethod1() {
    // Code goes here
  }

  @Version(major = 1, minor = 2)
  @Deprecated
  public void testMethod2() {
    // Code goes here
  }
}

public class Main {
  public static void main(String[] args) {
    // Read annotation of class declaration
    Class<AccessAnnotation> c = AccessAnnotation.class;
    System.out.println("Annotations for class:" + c.getName());
    printAnnotations(c);

    // Read annotation of package declaration
    Package p = c.getPackage();
    System.out.println("Annotations for package:" + p.getName());
    printAnnotations(p);

    // Read annotation of method declaration
    System.out.println("Method annotations:");
    Method[] m = c.getDeclaredMethods();
    for (int i = 0; i < m.length; i++) {
      System.out.println("Annotations for method:" + m[i].getName());
      printAnnotations(m[i]);
    }
  }

  public static void printAnnotations(AnnotatedElement programElement) {
    Annotation[] annList = programElement.getAnnotations();
    for (int i = 0; i < annList.length; i++) {
      System.out.println(annList[i]);
      if (annList[i] instanceof Version) {
        Version v = (Version) annList[i];
        int major = v.major();
        int minor = v.minor();
        System.out.println("Found Version annotation: " + "major =" + major + ", minor=" + minor);
      }
    }
    System.out.println();
  }
}

Java - Accessing Annotations at Runtime

Introduction

Demo

Result