backport175 - Reading annotations

Reading annotations

Using the Annotations reader class

You can retrieve the backport175 annotations as well as regular Java 5 annotations (when running Java 5) at runtime using the API in the Annotations class.

You retreive the annotations by specifying the:

name of the annotations - this must be the fully qualified name of the annotation interface.
class or member that is annotated - this is the java.lang.Class (for class level annotations) or one of the member class in the java.lang.reflect.* package for member level annotations (methods, fields and constructors)

Here is a sample part of the API:

// class annotations
public static boolean isAnnotationPresent(Class annotation, Class klass)
public static Annotation getAnnotation(Class annotation, Class klass)
public static Annotation[] getAnnotations(Class klass)

// method annotations
public static boolean isAnnotationPresent(Class annotation, Method method)
public static Annotation getAnnotation(Class annotation, Method method)
public static Annotation[] getAnnotations(Method method)

...

The Annotation interface

All these methods in the Annotations reader class return an instance of the type org.codehaus.backport175.reader.Annotation.

This class has some useful methods like:

/**
 * Returns the annotation type, e.g. the annotation interface type.
 *
 * @return the type
 */
Class annotationType();

/**
 * Returns a string representation that is identical to the annotation 
 * that was parsed by the compiler.
 *
 * @return the string representation
 */
String toString();

But most likely you want to cast the instance to the correct annotation type (interface).

Example

Here is an example on how to read in the EJB 3 transaction annotation:

if (Annotations.isAnnotationPresent(javax.ejb.TransactionAttribute.class, method)) {

    Annotation annotation = Annotations.getAnnotation(javax.ejb.TransactionAttribute.class, method);

    javax.ejb.TransactionAttribute txAttribute = (javax.ejb.TransactionAttribute)annotation;
}

Notes

If an annotation has an element with a default value, the reflective API will off course gives you access to it if the

annotated class/member was not specifying it.

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Using the Annotations reader class

The Annotation interface

Example

Notes