[cdi-dev] [JBoss JIRA] (CDI-403) why decorator requires interface

Ondrej Mihályi (JIRA) issues at jboss.org
Sat May 28 14:58:00 EDT 2016

    [ https://issues.jboss.org/browse/CDI-403?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13244395#comment-13244395 ] 

Ondrej Mihályi commented on CDI-403:

I think that it is worth to remove the requirement on interface in CDI2.

It should be fairly easy to specify additional scenario, where the decorator can extend the decorated class => it would inherit all public methods as if all methods would be exposed by an interface, and would decorate all beans injected by their class instead of by interface.

Currently, the way to work around this is to declare such decorator using {{@Specialized}} + {{@Alternative}} and delegating to methods in predecessor.  This is confusing in the code, as the decorator pattern is implemented using to other patterns. And it is not the same as delegate to another injected delegate, as multiple decorators cannot be chained:

public class MyBeanDecorator extends MyBean {

  public String hello() {
     return super.hello() + ", world!";   // decorates by adding ", world!" after result of hello()

> why decorator requires interface
> --------------------------------
>                 Key: CDI-403
>                 URL: https://issues.jboss.org/browse/CDI-403
>             Project: CDI Specification Issues
>          Issue Type: Clarification
>            Reporter: Mathieu Lachance
> As discussed with Jozef Hartinger on the WELD forum thread (see forum reference and CDI-224),
> would it be possible to revisit why decorator requires an interface ?
> I do not understand the semantic difference between:
> 1. a decorator to be an abstract class which implements an interface, which delegate to the same interface. 
> 2. a decorator to be a concrete class which extends a another class, which delegates to the same class.
> Why 1. should be allowed and why 2. should be disallowed ?
> As stated in CDI-224, if there is no technical reason of disallowing 2., should it be then considerate as a vendor specific feature to support it whether or not ?
> It is kind of sad that only decorators requires an interface while all the others Java EE 6 features do not.
> Thanks,

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