Hi
On 29.07.2010, at 15:59, Hynek Mlnařík wrote:
> Hi,
>
> I have two questions. To start with a simple one - is there a way to let
> iPOJO create default (empty) component instances on demand when requested by
> @Requested annotation? I only found a possibility of explicit instantiation
> via @Instantiate annotation explicitly but the on-demand one would be nice.
No there is not @Requested annotation. The @Instantiate annotation declares an
instance. However:
- @Instantiate declares the instance BUT does not create the POJO object
(service object), which is created lazily. So, it's an empty shell until the
service object is required (if the component is not configure to be immediate).
- You can create iPOJO instances using the Factory service (exposed by all
'public' component types). If you need to handle lazy instance declarations,
you can still use this API to create instances on the fly.
>
> The second question might be linked to the previous one. I'd like to have a
> component (logger) that gets parametrized by requesting components. I found
> that a way to get it working might be using strategies like this:
>
> @Component
> @Provides(strategy="LoggerComponentStrategy")
> class LoggerComponent implements LoggerComponentInterface {
> ...
> }
>
> public class LoggerComponentStrategy extends ConfigurableCreationStrategy
> implements ServiceObjectFactory {
> @Override
> protected ServiceObjectFactory getServiceFactory(final InstanceManager
> manager) {
> return this;
> }
>
> @Override
> public Object getService(final ComponentInstance instance) {
> final String name =
> instance.getInstanceDescription().getComponentDescription().getName();
> return safelyCreateLogger(name);
> }
> ...
> }
>
> @Component
> @Instantiate
> class B {
> @Requires LoggerComponentInterface l;
> }
>
> B gets only instantiated when the LoggerComponent class is annotated with
> @Instantiate annotation, ie. there already exists a Logger instance in iPOJO
> manager. That empty instance however is not used (and never will): the
> obtained instance of Logger injected into B must be parametrized with "B"
> name. Is there any way to have B initialize with the correct logger without
> the necessity of that useless empty Logger instance?
The LoggerComponent instance should not be created until B is really requiring
the logger. So, the 'getService' method should not be called before 'l' is
accessed.
Did you see a different behavior ?
Regards,
Clement
>
> Thanks,
>
> --Hynek
>
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