From 61135ac4da4023b415aad4c90ea63b83fc57ad90 Mon Sep 17 00:00:00 2001
From: Anand kumar <anand.creativex@gmail.com>
Date: Wed, 7 Jun 2017 18:54:47 +0530
Subject: [PATCH] Change annotation parameters during runtime (#2006)

---
 .../java/reflection/DynamicGreeter.java       | 23 ++++++++
 .../com/baeldung/java/reflection/Greeter.java | 10 ++++
 .../java/reflection/GreetingAnnotation.java   | 58 +++++++++++++++++++
 .../baeldung/java/reflection/Greetings.java   |  6 ++
 4 files changed, 97 insertions(+)
 create mode 100644 core-java/src/main/java/com/baeldung/java/reflection/DynamicGreeter.java
 create mode 100644 core-java/src/main/java/com/baeldung/java/reflection/Greeter.java
 create mode 100644 core-java/src/main/java/com/baeldung/java/reflection/GreetingAnnotation.java
 create mode 100644 core-java/src/main/java/com/baeldung/java/reflection/Greetings.java

diff --git a/core-java/src/main/java/com/baeldung/java/reflection/DynamicGreeter.java b/core-java/src/main/java/com/baeldung/java/reflection/DynamicGreeter.java
new file mode 100644
index 0000000000..3776ef82e2
--- /dev/null
+++ b/core-java/src/main/java/com/baeldung/java/reflection/DynamicGreeter.java
@@ -0,0 +1,23 @@
+package com.baeldung.java.reflection;
+
+import java.lang.annotation.Annotation;
+
+public class DynamicGreeter implements Greeter {
+    
+    private String greet;
+
+    public DynamicGreeter(String greet) {
+        this.greet = greet;
+    }
+
+    @Override
+    public Class<? extends Annotation> annotationType() {
+        return DynamicGreeter.class;
+    }
+
+    @Override
+    public String greet() {
+        return greet;
+    }
+
+}
diff --git a/core-java/src/main/java/com/baeldung/java/reflection/Greeter.java b/core-java/src/main/java/com/baeldung/java/reflection/Greeter.java
new file mode 100644
index 0000000000..ede269528a
--- /dev/null
+++ b/core-java/src/main/java/com/baeldung/java/reflection/Greeter.java
@@ -0,0 +1,10 @@
+package com.baeldung.java.reflection;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+@Retention(RetentionPolicy.RUNTIME)
+public @interface Greeter {
+    
+    public String greet() default ""; 
+}
diff --git a/core-java/src/main/java/com/baeldung/java/reflection/GreetingAnnotation.java b/core-java/src/main/java/com/baeldung/java/reflection/GreetingAnnotation.java
new file mode 100644
index 0000000000..601306f5d2
--- /dev/null
+++ b/core-java/src/main/java/com/baeldung/java/reflection/GreetingAnnotation.java
@@ -0,0 +1,58 @@
+package com.baeldung.java.reflection;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Field;
+import java.lang.reflect.Method;
+import java.util.Map;
+
+public class GreetingAnnotation {
+   
+    private static final String ANNOTATION_METHOD = "annotationData";
+    private static final String ANNOTATION_FIELDS = "declaredAnnotations";
+    private static final String ANNOTATIONS = "annotations";
+
+    public static void main(String ...args) {
+        Greeter greetings = Greetings.class.getAnnotation(Greeter.class);
+        System.err.println("Hello there, " + greetings.greet() + " !!");
+
+        Greeter targetValue = new DynamicGreeter("Good evening");
+        //alterAnnotationValueJDK8(Greetings.class, Greeter.class, targetValue);
+        alterAnnotationValueJDK7(Greetings.class, Greeter.class, targetValue);
+        
+        greetings = Greetings.class.getAnnotation(Greeter.class);
+        System.err.println("Hello there, " + greetings.greet() + " !!");
+    }
+    
+    @SuppressWarnings("unchecked")
+    public static void alterAnnotationValueJDK8(Class<?> targetClass, Class<? extends Annotation> targetAnnotation, Annotation targetValue) {
+        try {
+            Method method = Class.class.getDeclaredMethod(ANNOTATION_METHOD, null);
+            method.setAccessible(true);
+
+            Object annotationData = method.invoke(targetClass);
+            
+            Field annotations = annotationData.getClass().getDeclaredField(ANNOTATIONS);
+            annotations.setAccessible(true);
+
+            Map<Class<? extends Annotation>, Annotation> map = (Map<Class<? extends Annotation>, Annotation>) annotations.get(annotationData);
+            map.put(targetAnnotation, targetValue);
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+    
+    @SuppressWarnings("unchecked")
+    public static void alterAnnotationValueJDK7(Class<?> targetClass, Class<? extends Annotation> targetAnnotation, Annotation targetValue) {
+        try {            
+            Field annotations = Class.class.getDeclaredField(ANNOTATIONS);
+            annotations.setAccessible(true);
+
+            Map<Class<? extends Annotation>, Annotation> map = (Map<Class<? extends Annotation>, Annotation>) annotations.get(targetClass);
+            System.out.println(map);
+            map.put(targetAnnotation, targetValue);
+            System.out.println(map);
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+}
diff --git a/core-java/src/main/java/com/baeldung/java/reflection/Greetings.java b/core-java/src/main/java/com/baeldung/java/reflection/Greetings.java
new file mode 100644
index 0000000000..4f3a20c3b9
--- /dev/null
+++ b/core-java/src/main/java/com/baeldung/java/reflection/Greetings.java
@@ -0,0 +1,6 @@
+package com.baeldung.java.reflection;
+
+@Greeter(greet="Good morning")
+public class Greetings {
+
+}