[cdi-dev] [JBoss JIRA] (CDI-493) Allow firing of parameterized event types from BeanManager

Sven Linstaedt (JIRA) issues at jboss.org
Mon Jan 5 05:10:30 EST 2015

     [ https://issues.jboss.org/browse/CDI-493?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sven Linstaedt updated CDI-493:
    Summary: Allow firing of parameterized event types from BeanManager  (was: Allow firing of generic events from BeanManager)

> Allow firing of parameterized event types from BeanManager
> ----------------------------------------------------------
>                 Key: CDI-493
>                 URL: https://issues.jboss.org/browse/CDI-493
>             Project: CDI Specification Issues
>          Issue Type: Feature Request
>          Components: Events
>    Affects Versions: 1.2.Final
>            Reporter: Sven Linstaedt
> Currently we are allowed firing generic events from {{javax.enterprise.event.Event<X>#fire}} as long as it's type parameter X does not contain a TypeVariable. 
> When it comes to {{javax.enterprise.inject.spi.BeanManager#fireEvent}} and {{javax.enterprise.inject.spi.BeanManager#resolveObserverMethods}} this is unfortunately not possible due to type erasure. Because we lack the relevant generic information that are otherwise explicit stated via {{Event#select}}, we are not able to fire a generic event from {{BeanManager#fireEvent}}.
> This proposal is about enhancing the API of BeanManager in order to supply the relevant type information, that are otherwise discarded by type erasure. A possible solution would look like adding two new methods to BeanManager
> {code}
> BeanManager#fireEvent(Type, Object, Annotation...)
> BeanManager#resolveObserverMethods(Type, T, Annotation...)
> {code}
> which receive the selected event type as 1st parameter, validate that the actual event instance (2nd parameter) is assignable to the selected event type (the selected event type has to resolve all type variables; throwing an IllegalArgumentException otherwise) and fires the event afterwards.
> The original two methods can delegate their calls to the new ones, having {{java.lang.Object}} as event type. 
> Additionally {{javax.enterprise.inject.spi.EventMetadata#getType()}} will return the resolved parameterized type.
> With this proposal it would be possible to provide meta-extensions, that enable other extension to handle custom extension lifecycle events like 
> {code}
> <X> void on(@Observes @BoundWith(InterceptorBinding.class) ProcessBoundedType<X> pbt) {
>     if (pbt.getBoundedType().isAnnotationPresent(Interceptor.class)) {
>         // register interceptor type
>     } else {
>         // register intercepted type
>     }
> }
> {code}

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