[
https://issues.apache.org/jira/browse/FELIX-5749?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16260953#comment-16260953
]
Neil Bartlett commented on FELIX-5749:
--------------------------------------
This is impossible at a Java level, so do you have a new problem statement or
can we close this Jira?
> Allow to use components that depend on optional imports
> -------------------------------------------------------
>
> Key: FELIX-5749
> URL: https://issues.apache.org/jira/browse/FELIX-5749
> Project: Felix
> Issue Type: New Feature
> Affects Versions: scr-2.0.12
> Reporter: Christian Schneider
>
> When desigining the scope of a bundle you sometimes have an optional part
> that could be externalized into its own bundle but you decide to keep it in
> your bundle to limit the number of bundles. In this case you have to use an
> optional import and make sure the code that depends on this import only runs
> when this import is wired. This code is often quite awkward and often also
> buggy.
> We discussed on osgi-dev that you can make such code a lot simpler to write
> by using DS.
> This is how the code would look like:
> You externalize the code that depends on the optional import into one or more
> components. These components offer a service interface that is not dependent
> on the optional import. Inside the component you can work freely with the
> optional packages. You have to make sure this component is disabled by
> default. Then you write a "starter" component that enables the component if
> the package is available.
> I think scr could support such "optional" components without the disabled
> trick. We could load the component class and if it fails disable the
> component. If it works we enable it.
> So if the package is wired later and we get a refresh this approach would
> activate the component without any additional effort from the developer side.
> ----
> Below I am copying a snippet from Ray that details what they did.
> Given your component which has the optional import package (doesn't matter
> how it's used):
> import com.liferay.demo.foo.Foo; // The optional package
> @Component(
> enabled = false // disable by default so DS ignores it
> )
> public class OptionalPackageConsumer implements Foo {...}
> Make sure the component is disabled by default. This will prevent SCR from
> classloading the component class.
> Second, you construct a "starter" component who's job it is to check for the
> available package:
> @Component
> public class OptionalPackageConsumerStarter {
> @Activate
> void activate(ComponentContext componentContext) {
> try {
> Class.forName(com.liferay.demo.foo.Foo.class.getName());
>
> componentContext.enableComponent(OptionalPackageConsumer.class.getName());
> }
> catch (Throwable t) {
> _log.warn("Could not find {}", t.getMessage());
> }
> }
> }
--
This message was sent by Atlassian JIRA
(v6.4.14#64029)
