[javaee-spec users] [jsr342-experts] Re: managed bean alignment

From: Pete Muir <>
Date: Tue, 10 Apr 2012 16:50:05 +0100


I've already extensively discussed this topic with you and Bill when we did a lot of the groundwork for this email, but for the record, our (JBoss') opinion is that Option (2a) is the most preferable. We also see this as an iterative process, we may not sort it all out in this round, but need to make steps forward!

There have been calls for a fully unified underlying managed bean model for all components, that offers all of CDI services (e.g. observers, interceptors). Had this been designed in from day 1, it could make sense, but many technologies have solved the lack of a set of core services by defining ad-hoc, domain specific alternatives (such as MDBs or servlet filters/listeners). We believe it would be very confusing to try to unify all of these at this point in time, as it would offer at least 2 ways to do everything, with no clear advantage (people already know and have documented very well the existing approaches).

We also see little value in the ability for users to be able to define a managed bean themselves, and would prefer this to be an abstract description of a set of core services, that also provides guidelines for how to build on top of it. This would promote unification going forward.

Our second choice would be Option (2), and we're not keen on any of the other options.


On 29 Mar 2012, at 22:52, Linda DeMichiel wrote:

> One of the issues we're grappling with in this release is better alignment
> between Java EE and CDI in the treatment of managed beans.
> There has been some confusion in the community as to what a Java EE
> Managed Bean is, and how Java EE Managed Beans relate to CDI.
> Java EE 6 introduced the Managed Beans specification in order to
> better define a spectrum of functionality applicable to Java EE
> managed objects. Basic Managed Beans are container-managed objects
> with minimal requirements that support a small set of basic services,
> such as resource injection, lifecycle callbacks, interceptors, and the
> ability to be looked up in JNDI or injected.
> Modifications of the basic Managed Beans model that are allowed and
> explicitly foreseen by the Managed Bean specification include:
> * Other ways to declare Managed Beans
> * Other ways to declare constructors of Managed Beans
> * Other ways to assign a name to a Managed Bean
> * Other lifecycle models
> * The ability to have an own java:comp namespace
> * The ability to specify other threading requirements
> * The ability to have a different interceptor facility
> In defining Managed Beans this way, our intention has been to
> cover a spectrum of common functionalities under which to align
> our component models as they evolve.
> CDI managed beans are also defined very minimally: they are required
> to have a no-arg constructor or a constructor annotated @Inject. (See
> CDI 3.1.1 for a more precise definition).
> CDI managed beans support the following functionality (not intended as
> an exhaustive list): they are contextual objects, having a
> well-defined lifecycle or scope that is managed by CDI; they can have
> other beans and resources be injected into them; they can be injected
> into other managed objects; they can have qualifiers, which support
> type-safe injection; they can have interceptors, decorators, and
> observer methods; they can have producer methods and producer fields,
> which in turn can be sources of other managed beans.
> Because CDI managed beans are defined so minimally--any class that has
> a no-arg constructor can be a CDI managed bean--many of the Java EE
> managed classes, in particular those listed in Table EE.5-1 of the
> Java EE specification ("Component classes supporting injection"), can
> be treated as CDI managed beans. Today, however, only Session Beans
> retain their platform-defined component behaviors when treated as CDI
> managed beans. Thus, for example, while a Servlet class (annotated
> with @WebServlet) can be injected with @Inject into a CDI managed bean
> or into an EJB, the instance that is injected does not have the
> ability to service HTTP requests.
> See the attached file Matrix1, which attempts to characterize the
> managed classes of the Java EE platform with regard to CDI
> functionality in a more graphic way. This is as things stand today.
> Notice that while some CDI functionality that is applicable to CDI
> managed beans (including sessions beans) has been extended beyond
> these types, it is not extended in a uniform way. For example,
> Message Driven Beans support CDI interceptors, although they don't
> support the other CDI functionality that session beans do.
> There is also an alignment issue within the Java EE component types
> themselves (EJBs, Servlets, JAX-RS resource classes, web service
> endpoints). For example, only EJBs currently and ManagedBeans support
> Java EE interceptors. JAX-RS endpoints support interceptors if their
> implementation class is an EJB or a ManagedBean. Web service endpoints
> support interceptors if their implementation class is an EJB.
> We think the current state of affairs needs clarification, and would
> like to find a way to better align the notions of CDI managed bean,
> Java EE Managed Bean, and Component class supporting injection.
> We see several possibilities.
> (1) "Do-nothing option"
> Do nothing except add clarification to the Platform specification
> that only EJB session bean (and, trivially, @ManagedBean) components
> retain their Java EE defined component behaviors when used as CDI
> managed beans.
> (2) "First- and second- class managed objects option"
> Distinguish two distinct groups of what are currently referred to
> in Table EE.5.1. as "component classes": Components and auxiliary
> component classes. As suggested in the earlier discussion in this
> expert group, define the notion of "Component class" (used in Table
> EE.5.1) more narrowly around the current component types: EJB,
> Servlet, Managed Bean, and Java EE managed classes using these as
> implementation types (JAX-RS resource classes and web service
> endpoints). In other words, distinguish two distinct groups of what
> the specification currently characterizes as "component classes":
> component classes proper, and auxiliary component classes (e.g.,
> filters, listeners, interceptors, ...). In addition, align the notion
> of Java EE Managed Beans around container services that such types
> would support (or do already support): such as container-managed
> transactions, container-managed security, async invocation, and
> timers/timerservice. Such services would extend also to CDI managed
> beans, but Java EE components other than Session Beans and Managed
> Beans would not retain their Java EE component behaviors when used as
> CDI managed beans. Note that container-managed transactions,
> container-managed security, and async invocation are candidates for
> support via CDI interceptors. It would be desirable if we could
> support timer service notifications as container-managed events using
> the CDI event/observer functionality.
> Matrix2 illustrates this. The blue background highlights the
> changes from Matrix1. The functional change to the initial matrix is
> that interceptor support would be extended to Servlets and JAX-RS
> resource classes and more uniformly to EJBs and Managed Beans. (While
> I've included timer support in this matrix as well, to illustrate how
> these capabilities could evolve, we have no current plans to enhance
> timer support in Java EE 7.)
> Notice that this also removes the anomaly with regard to the treatment
> of MDBs that I mentioned above. It has the disadvantage, however,
> that CDI features are still not uniformly supported for Java EE components.
> (2a) "Option 2 + prune the Managed Bean spec option"
> Abandon the attempted generalizations of Managed Beans in Section
> MB.2.2 of the Managed Beans specification, and define Java EE
> ManagedBeans in terms of the "Basic Model" only. [This is the same
> matrix as Matrix2.]
> (3) "More CDI functionality extended into Java EE Components option"
> In addition to the changes in (2), attempt to merge the notions of
> Java EE Managed Beans and CDI managed beans so that the other Java EE
> component types support more of the CDI functionality (i.e.,
> interceptors, decorators, observer methods, producer methods/fields),
> while retaining their behavior as Java EE components. An exception
> here might be made for the ability to inject these into other
> components while preserving their Java EE behavior. For example,
> injection into other beans might be restricted to those components
> that support a local view rather than remote invocation via HTTP, web
> services, JMS, RMI, etc.
> Matrix3 illustrates this. The green background highlights the
> changes beyond Matrix2.
> (4) "Injected components behave as components"
> In addition to (3), Java EE components retain their component
> behavior when injected. For example, the Servlet instance that would
> be obtained via injection would be the same Servlet instance that the
> web container was using to service HTTP requests, and similarly for the
> other Java EE component types.
> Matrix4 illustrates this, using the purple background to highlight
> the changes beyond Matrix3.
> (5) "All Java EE component classes become Java EE ManagedBeans option"
> In addition to the changes in (2), extend the notion of Java EE
> ManagedBean to all container managed classes in Table EE.5.1. In
> addition to resource injection (which these classes already support),
> they would also have lifecycle callbacks, interceptors, timer support,
> and the ability to be looked up in JNDI. The functional change is
> that servlet filters, listeners, interceptors, etc. would get
> these features.
> Matrix5 illustrates the change in functionality. The pink background
> highlights the changes beyond Matrix2.
> (6) "Everything is a managed bean option"
> Both first- and second-class managed classes support CDI managed bean
> capabilities.
> Matrix 6 illustrates this. It includes the features of both Matrix4
> and Matrix5. The yellow background highlights the addition of CDI
> functionality beyond the features of Matrix4 and Matrix5.
> We need your feedback!!
> We realize that this is a lot of information to digest, but we really
> need you to consider it all carefully and to provide your feedback.
> These issues have very considerably impact on how we go forward with
> managed bean support in the Java EE Platform.
> thanks,
> -Linda