Is it possible to access Java 8 type information a

问题:

Assuming I have the following member in a class which makes use of Java 8 type annotations:

private List<@Email String> emailAddresses;

Is it possible to read the @Email annotation given on the String type use at runtime using reflection? If so, how would this be done?

Update: That's the definition of the annotation type:

@Target(value=ElementType.TYPE_USE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Email {}

回答1:

Yes it is possible. The reflection type representing this kind of structure is called AnnotatedParameterizedType. Here is an example of how to get your annotation:

// get the email field 
Field emailAddressField = MyClass.class.getDeclaredField("emailAddresses");

// the field's type is both parameterized and annotated,
// cast it to the right type representation
AnnotatedParameterizedType annotatedParameterizedType =
        (AnnotatedParameterizedType) emailAddressField.getAnnotatedType();

// get all type parameters
AnnotatedType[] annotatedActualTypeArguments = 
        annotatedParameterizedType.getAnnotatedActualTypeArguments();

// the String parameter which contains the annotation
AnnotatedType stringParameterType = annotatedActualTypeArguments[0];

// The actual annotation
Annotation emailAnnotation = stringParameterType.getAnnotations()[0]; 

System.out.println(emailAnnotation);  // @Email()