Re: Reflection and Annotation-arguments

Daniel Pitts <>
Mon, 28 Sep 2009 09:49:24 -0700
Mayeul wrote:

grz01 wrote:

Hi again,

Another reflection question...

I can get at the annotations of a class by doing something like:

    import java.lang.annotation.Annotation
    Bean bean = new Bean();
    Annotation a = bean.getClass().getAnnotations()[0];

But if the Annotation has parameters, like

   public class Bean{ ... }

how do I extract the argument here (i e: name = "FOOBAR") ?

Looking at the java.lang.annotation.Annotation class, I dont see any
method for this?

That is because annotations extend the java.lang.annotation.Annotation
interface, and declare by themselves the parameters they accept, in the
form of parameterless methods.

Since your Table annotation accepts a 'name' parameter, it defines at
least a name() method, which probably returns a String.
You need to cast your Annotation object to Table and call this name()
method on it.

You can call the annotationType() method if you're not sure what to cast
your Annotation to. It is also possible to inspect the methods provided
by annotation classes, and to get an annotation's parameters values by
invoking those methods on an Annotation object.


Annotation a = bean.getClass().getAnnotations()[0];
Table table = (Table)a;
String name =;
System.out.println(name); // Should display FOOBAR

Generally, you ask for an annotation by type, rather than look at the
available annotations:

Table table = bean.getClass().getAnnotation(Table.class);

If you don't know the type before hand, then you can use reflection on
the returned object to get the public methods, and call those.

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