[cdi-dev] [JBoss JIRA] Commented: (CDI-110) Provide support for binding an invocation handler to an interface or abstract class

Richard Hightower (JIRA) jira-events at lists.jboss.org
Thu Sep 29 23:22:26 EDT 2011

    [ https://issues.jboss.org/browse/CDI-110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12631442#comment-12631442 ] 

Richard Hightower commented on CDI-110:

Forgive the over explanation, just trying to be clear....

An interceptor typically intercepts concrete classes.
Say LibraryServiceImpl needs a LogInterceptor, or a TransactionInterceptor, or whatever.

The interceptor is sort of a dynamic decorator design pattern instead of implementing the same interface as the service impl, it uses reflection constructs so that it can intercept any concrete class (ignore CDI decorators for a moment) with the same cross cutting service I.e, logging, transactions, security, etc.

So later the same two interceptors can implement the BankServiceImpl (class).

Ok at this point hopefully we are on the same page....

What I am asking and hoping is that I can have an interceptor intercept calls to an interface like LibraryService and use the same constructs to provide an implementation of an arbitrary interface ( or any abstract class).

Thus there is no final proceed. The interceptor is the implementation. So if I wanted to provide an interceptor that translated method calls into REST calls then I could have an interceptor called RESTInterceptor that decorates the LibraryService interface and I can intercept calls and turn those into rest calls for a remote client automatically where LibraryService is an interface and nor a class. I could also intercept calls to LibraryService with JMSInterceptor and implement the methods by sending JMS messages.

In the past I used this technique with Spring interceptors to create methods on the fly that accessed JPA named queries. You could also do this with mixin support.

The plumbing is there already. The leap from implementing interceptors for concrete classes to intercepting interfaces so that the interfaces have an implementation is not that far off in scope or implementation.

AspectJ has it. Spring 1.0 has it. Spring 2 improved it. I think CDI should have it.

I thought I saw someone discussing it for CDI 1.1 at some point and thought it would be in the summary.

> Provide support for binding an invocation handler to an interface or abstract class
> -----------------------------------------------------------------------------------
>                 Key: CDI-110
>                 URL: https://issues.jboss.org/browse/CDI-110
>             Project: CDI Specification Issues
>          Issue Type: Feature Request
>          Components: Inheritance and Specialization
>    Affects Versions: 1.0
>            Reporter: George Gastaldi
>            Assignee: George Gastaldi
>              Labels: cdi
>             Fix For: 1.1 (Proposed)
> The purpose of this feature is to allow interfaces and abstract classes to be automatically implemented by an invocation handler to which all abstract method invocations are delegated. The invocation handler would get "bound" to the type using the same strategy as is used for interceptor binding.
> Binding type:
> {code:java}
> @Target({ METHOD, TYPE })
> @Retention(RetentionPolicy.RUNTIME)
> @ServiceHandlerBindingType
> public @interface EchoService {}
> {code}
> Invocation handler:
> {code:java}
> @ServiceHandler
> @EchoService
> public class EchoServiceHandler {
>     @AroundInvoke
>     public Object invoke(InvocationContext ctx) {
>         return ctx.getMethod().getName().toString();
>     }
> }
> {code}
> Usage:
> {code:java}
> @EchoService
> public interface HelloWorld {
>    String helloWorld();
> }
> {code}

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