Hi,
On 17 oct. 2013, at 19:32, Hendrik Nunner <[email protected]>
wrote:
> Dear Felix Team,
>
> we came across an unsupported feature we would like to use, while using iPOJO
> service injection. When defining a service via the @Requires annotation it is
> possible to define a fallback service at the same time ("defaultclass" being
> a Class object). When this property is left out, iPOJO provides a default
> service using a Java Proxy
> (org.apache.felix.ipojo.handlers.dependency.NullableObject). This proxy
> delivers hard-coded default values (0 or false) according to the requested
> return type.
>
> Our goal is to use a custom Proxy as fallback service. This proxy can
> generically handle methods for different use cases. This would be great, for
> example, for services that are not able to provide certain aspects of their
> functionality by throwing an exception, whereas other aspects can be
> implemented by returning a default value different to 0 or false.
Isn't this 'default-implementation'
(http://felix.apache.org/documentation/subprojects/apache-felix-ipojo/apache-felix-ipojo-userguide/describing-components/service-requirement-handler.html#optional-scalar-dependencies-no-service-actions)
? Default-implementation are an implementation of the service interface used
when no provider are available. This implementation is specified in the
@Requires annotation. Unlike nullable object, default-implementation can
contain code.
For example:
@Requires(optional=true, nullable=true)
private LogService nullableLog;
@Requires(optional=true,
default_implementation=MyImplementationOfLogService.class)
private LogService diLog;
//...
nullableLog.log(LogService.INFO, "message"); // does nothing, a nullable do not
have a real logic
diLog.log(LogService.INFO, "message"); // Can, for example, print the message
on System.out
>
> One idea to achieve this, could be by implementing a new iPOJO interface
> extending InvocationHandler (with
> org.apache.felix.ipojo.handlers.dependency.NullableObject being a subclass
> of). Another idea would be by defining another property for the @Requires
> annotation, which will be checked and handled inside
> org.apache.felix.ipojo.handlers.dependency.Dependency.start().
>
> Maybe you guys came across this request before and came up with a solution
> already. Or mabye you have different ideas to achieve this feature. We would
> be more than happy to discuss this idea with you or implement this feature
> ourselves.
>
I think that what' you are trying to implement is close to
default-implementation.
However, I recently discussed with another iPOJO user about the ability to
customize the object injected when no services are available. This request have
been postponed until we analyze more deeply the use cases. If you come up with
such use case, we would be very happy to discuss such feature.
Best regards,
Clement
> Best regards,
> Hendrik Nunner
