Java Reference
In-Depth Information
<interceptors>
<class>billpayment.interceptors.LoggedInterceptor</class>
</interceptors>
If an application uses more than one interceptor, the interceptors are invoked in the order
specified in the
beans.xml
file.
Using Decorators in CDI Applications
A
decorator
is a Java class that is annotated
javax.decorator.Decorator
and that
has a corresponding
decorators
element in the
beans.xml
file.
A decorator bean class must also have a delegate injection point, which is annotated
javax.decorator.Delegate
. This injection point can be a field, a constructor
parameter, or an initializer method parameter of the decorator class.
Decorators are outwardly similar to interceptors. However, they actually perform tasks
complementary to those performed by interceptors. Interceptors perform cross-cutting
tasks associated with method invocation and with the lifecycles of beans, but cannot per-
form any business logic. Decorators, on the other hand, do perform business logic by inter-
cepting business methods of beans. This means that instead of being reusable for different
kinds of applications as are interceptors, their logic is specific to a particular application.
For example, instead of using an alternative
TestCoderImpl
class for the
encoder
example, you could create a decorator as follows:
@Decorator
public abstract class CoderDecorator implements Coder {
@Inject
@Delegate
@Any
Coder coder;
public String codeString(String s, int tval) {
int len = s.length();
return "\"" + s + "\" becomes " + "\"" + coder.codeString(s,
tval)
+ "\", " + len + " characters in length";
}
}
