Interesting questions Fahim, let me try to answer them, or at least
give my understanding os possible use cases for these features in
question:
2008/10/6 fahim salim <[EMAIL PROTECTED]>:
> Hi
>
> I have some points concerning SCA Java Component Implementation
> Specification that I'd like to clarify.
>
> 1/ use of @Service annotation (p. 2)
> In this document, it is said that a service offered by a component can be
> defined in two ways :
>
> a/ by an interface
>
> @Service (HelloService.class)
> Public class HelloServiceImpl implements HelloService {
> public String hello(String message) {
> …
> }
> HelloService.java (interface) defines the method implemented by the
> component in HelloServiceImpl.java
>
> b/ by a class
>
> @Service (HelloServiceImpl.class)
> Public class HelloServiceImpl implements AnotherInterface {
> public String hello(String message) {
> …
> }
> In this case the java class itself defines the service offered by the
> component
>
>
> my question : Why to have such a choice ? Is an interface not enough to
> define service offered by a component ?
>
I can imagine that the option to introspect the service contract from
the implementation class would be usefull when you are exposing a
service from a jar that you don't have access to the source code, and
it was implemented as a pojo. I think there are also talks to make
interfaces optional in EJB 3.1, this might be another use case for
this feature.
>
> 2/ use of @Reference annotation(p.4)
>
> we can use @Reference in one of the following ways :
>
> a/ with setter method
>
> public class MyClientImpl implements MyClient{
>
> private MyService myService;
>
> @Reference
> public void setMyService(MyService myService) {
> this.myService = myService;
> }
>
> b/ with field injection
>
> public class MyClientImpl implements MyClient{
> @Reference (name="myService")
> protected MyService myService;
> ...
> }
>
> where myService is the reference to a service used by MyClient component
>
> my question : Why and when to prefer setter method than field injection ?
While using fields, they would be injected with the reference and
that's it. If you use setters, you can get injected and perform
further operations/configurations as needed in the set method.
>
> 3/ References (p.4)
>
> Do we have two distinct manners of obtaining references? One through
> injection and one through ComponentContextAPI ?
>
> Thanks
> Fahim
>
>
>
>
--
Luciano Resende
Apache Tuscany, Apache PhotArk
http://people.apache.org/~lresende
http://lresende.blogspot.com/
