get annotation value?

Question

How do you get values set inside a annotation?

I have the following annotation defined:

@Target(ElementType.METHOD) @Retention(RetentionPolicy.RUNTIME) public @interface JsonElement { int type(); }

And here is the method that uses it in a POJO class

@JsonElement(type=GETTER_METHOD) public String getUsername{ ........................ }

And the util class that uses reflection to check if this method has the JSonElement annotation present and to check what the type value is.

Method methods[] = classObject.getClass().getDeclaredMethods(); JSONObject jsonObject = new JSONObject(); try { for (int i = 0; i < methods.length; i++) { String key = methods[i].getName(); System.out.println(key); if (methods[i].isAnnotationPresent(JsonElement.class) && key.startsWith(GET_CHAR_SEQUENCE)) { methods[i].getDeclaredAnnotations(); key = key.replaceFirst(GET_CHAR_SEQUENCE, ""); jsonObject.put(key, methods[i].invoke(classObject)); } } return jsonObject; } catch (Exception e) { e.printStackTrace(); return null; }

How do I find out what type() value is? I can find whether the annotation is present, but I can't find a method that finds out what value - if any - was set for type().

Petr Janeček · Accepted Answer · 2012-05-21 10:20:06Z

JsonElement jsonElem = methods[i].getAnnotation(JsonElement.class); int itsTypeIs = jsonElem.type();

Note that you must be sure that jsonElem is not null either by your

isAnnotationPresent(JsonElement.class)

or a simple

if (jsonElem != null) { }

check.

Additionally, if you changed your annotation to

public @interface JsonElement { int type() default -1; }

you wouldn't have to state the type attribute at every occurence of @JsonElement in your code - it would default to -1.

You could also consider using an enum for this instead of some integer flags, for example:

public enum JsonType { GETTER, SETTER, OTHER; } public @interface JsonElement { JsonType type() default JsonType.OTHER; }

yes i got it working; thanks. is their a way to make the "type()" optional? As of now, type() has to be declared in the JsonElement annotation

mprabhat · Accepted Answer · 2012-05-21 09:58:31Z

You can check if annotation belongs to JSonElement if yes you can cast and call your methods

If looping through all the annotation then

for(Annotation annotation : methods[i].getAnnotations()) { if(annotation instanceOf(JsonElement)){ ((JsonElement)annotation).getType(); } }

or

JSonElement jSonElement = methods[i].getAnnotations(JSonElement.class); jSonElement.getType();

Mariusz Jamro · Accepted Answer · 2013-11-21 21:02:08Z

2

JsonElement jsonElement = methods[i].getAnnotation(JsonElement.class); int type = jsonElement.type();

edited Nov 21, 2013 at 21:02

Mariusz Jamro

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answered May 21, 2012 at 9:55

maress

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Comments

Jono · Accepted Answer · 2012-05-21 10:06:16Z

solution:

 Method methods[] = classObject.getClass().getDeclaredMethods(); JSONObject jsonObject = new JSONObject(); try { for (int i = 0; i < methods.length; i++) { String key = methods[i].getName(); System.out.println(key); if (methods[i].isAnnotationPresent(JsonElement.class) && key.startsWith(GET_CHAR_SEQUENCE) && (methods[i].getAnnotation(JsonElement.class).type() == GETTER_METHOD)) { key = key.replaceFirst(GET_CHAR_SEQUENCE, ""); jsonObject.put(key, methods[i].invoke(classObject)); } } return jsonObject; } catch (Exception e) { e.printStackTrace(); return null; }

kopfpilot · Accepted Answer · 2013-06-13 10:15:45Z

From what i understood, your code does: - iterate over the declared methods - check if current method is annoted with JsonElement.class, its name starts with GET_CHAR_SEQUENCE and the value of annotation type is equal to GETTER_METHOD. - you build your json according conditions

i can't see that you are changing the currenty value of the type member of the annotation itself. Seemes like you did not need it anymore.

But does anyone know how to get this task sorted out?

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