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Weld Extensions provides a number of utilility classes to make working with Annotations and AnnotatedTypes easier. This chapter will walk you each utility, and give you an idea of how to use it. For more detail, take a look at the javaodoc on each class.
Weld Extensions provides an AnnotatedType implementation that should be suitable for most
portable extensions needs. The AnnotatedType is created from
AnnotatedTypeBuilder as follows:
AnnotatedTypeBuilder builder = new AnnotatedTypeBuilder()
.readFromType(baseType,true) /* readFromType can read from an AnnotatedType or a class */
.addToClass(ModelLiteral.INSTANCE) /* add the @Model annotation */
.create();
Here we create a new builder, and initialize it using an existing AnnotatedType. We can then
add or remove annotations from the class, and it's members. When we have finished modifying the type, we call
create() to spit out a new, immutable, AnnotatedType.
AnnotatedTypeBuilder also allows you to specify a "redefinition" which can be applied to the
type, a type of member, or all members. The redefiner will receive a callback for any annotations present which
match the annotation type for which the redefinition is applied. For example, to remove the qualifier
@Unique from any class member and the type:
AnnotatedTypeBuilder builder = new AnnotatedTypeBuilder()
.readFromType(baseType,true)
.redefine(Unique.class, new AnnotationRedefiner<Unique>() {
public void redefine(RedefinitionContext<A> ctx) {
ctx.getAnnotationBuilder().remove(Unique.class);
}
}
.create();
Sometimes you may need an annotation instance for an annotation whose type is not known at development time.
Weld extends provides a AnnotationInstanceProvider class that can create an
AnnotationLiteral instance for any annotation at runtime. Annotation attributes
are passed in via a Map<String,Object>. For example given the follow annotation:
@Retention(RetentionPolicy.RUNTIME)
public @interface MultipleMembers {
int intMember();
long longMember();
short shortMember();
float floatMember();
double doubleMember();
byte byteMember();
char charMember();
boolean booleanMember();
int[] intArrayMember();
}
We can create an annotation instance as follows:
/* Create a new provider */
AnnotationInstanceProvider provider = new AnnotationInstanceProvider();
/* Set the value for each of attributes */
Map<String, Object> values = new HashMap<String, Object>();
values.put("intMember", 1);
values.put("longMember", 1);
values.put("shortMember", 1);
values.put("floatMember", 0);
values.put("doubleMember", 0);
values.put("byteMember", ((byte) 1));
values.put("charMember", 'c');
values.put("booleanMember", true);
values.put("intArrayMember", new int[] { 0, 1 });
/* Generate the instance */
MultipleMembers an = provider.get(MultipleMembers.class, values);
The Annotation Inspector allows you to easily discover annotations which are meta-annotated. For example:
/* Discover all annotations on type which are meta-annotated @Constraint */
Set<Annotation> constraints = AnnotationInspector.getAnnotations(type, Constraint.class);
/* Load the annotation instance for @FacesValidator the annotation may declared on the type, */
/* or, if the type has any stereotypes, on the stereotypes */
FacesValidator validator = AnnotationInspector.getAnnotation(
type,
FacesValidator.class,
true,
beanManager);
When developing an extension to CDI, it can be useful to detect certain injection points, or bean definitions and based on annotations or other metadata, add qualifiers to further disambiguate the injection point or bean definition for the CDI bean resolver. Weld Extension's synthetic qualifers can be used to easily generate and track such qualifers.
In this example, we will create a synthetic qualifier provider, and use it to create a qualifier. The provider will track the qualifier, and if a qualifier is requested again for the same original annotation, the same instance will be returned.
/* Create a provider, giving it a unique namespace */
Synthetic.Provider provider = new Synthetic.Provider("com.acme");
/* Get the a synthetic qualifier for the original annotation instance */
Synthetic synthetic = provider.get(originalAnnotation);
/* Later calls with the same original annotation instance will return the same instance */
/* Alternatively, we can "get and forget" */
Synthetic synthetic2 = provider.get();
Weld Extensions comes with a number miscellaneous reflection utilities; these extend JDK reflection, and some
also work on CDI's Annotated metadata. See the javadoc on Reflections for more.
InjectableMethod allows an AnnotatedMethod to be injected with parameter values
obtained by following the CDI type safe resolution rules, as well as allowing the defautl aparameter values to
be overridden.