[cdi-dev] [JBoss JIRA] (CDI-248) Provide means to observe a group of qualified events ("Qualifier Inheritance"?)

[Jens Schumann (JIRA)]

Jens Schumann created CDI-248:
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             Summary: Provide means to observe a group of qualified events ("Qualifier Inheritance"?) 
                 Key: CDI-248
                 URL: https://issues.jboss.org/browse/CDI-248
             Project: CDI Specification Issues
          Issue Type: Feature Request
          Components: Concepts, Events
            Reporter: Jens Schumann


We have been using CDI events for application development quite extensively. For instance we use events to propagate entity lifecycle events (@Created/@Updated/@Deleted Customer customer) or GUI selections (@Selected/@Deselected Customer customer) and implement related business logic in event observers. (e.g. send email for newly created customers, clear cached values on select/deselect/create/update/delete ...).

This works quite well, however we have noticed that especially our JSF Presentation Tier contains lots of observer methods implementing the same behavior for a group of related CDI events. 

Example:

{code}
public class XyzBean {

 public void onCustomerCreate(@Observes @Created Customer customer) { reset();} 
 public void onCustomerUpdate(@Observes @Updated Customer customer) { reset();} 
 public void onCustomerDelete(@Observes @Deleted Customer customer) { reset();}
 
}
{code}

Looks ugly, doesn't it? 

The above example could be improved if CDI would be able to observe a group of qualified events, e.g. public void onCustomerLifeCycleEvent(@Observes @LifeCycleChange Customer customer) { reset(); } - ignore method and qualifier names for now.

Since Java does not support annotation inheritance grouping could be achieved using "qualified qualifier annotations": 

{code}
@Qualifier
public @interface LifeCycleChange

@Qualifier
@LifeCycleChange
public @interface Created

@Qualifier
@LifeCycleChange
public @interface Updated

@Qualifier
@LifeCycleChange
public @interface Deleted


@Qualifier
public @interface SelectionChange

@Qualifier
@SelectionChange
public @interface Selected

@Qualifier
@SelectionChange
public @interface Deselected
{code}


WDYT? Side effects? Problems? 

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