Firstly, I am glad we are finally getting to this very critical issue. Secondly, thanks for doing such a thorough job analyzing this.
This is an issue we've discussed extensively and repeatedly at Caucho and hence I can offer what I think is a fairly well thought out opinion. Unfortunately, it can't be as simple as picking one of the matrices. I hope you'll forgive me and try to find a way of reconciling what I have below:
* Java EE Managed Beans:
We found that the @ManagedBean annotation is actually a source of confusion/frustration for most developers. I think it's best to gradually prune this annotation or simply leave it be. The overall concept is very good though and definitely should be kept around. The way we look at it, the fundamental concept serves as the unifying component model whereas all the other Java EE APIs can add their own services, including CDI. The basic question then really becomes which Java EE services are "legal" to be used on the very same managed bean. You could think of this as a kind of "service compatibility" matrix, in a much similar vein to yours.
* @Resource, @EJB:
These two annotations are largely redundant with CDI. It's best to gradually prune these annotations or simply leave them be. We should try to find a way of merging whatever remaining functionality they have with CDI.
* Java EE interceptors:
These were a fairly hasty and poor attempt at addressing cross-cutting concerns. It's best to gradually prune this or simply leave them be and focus on CDI annotations. Alternatively, perhaps CDI annotations should be merged back with this (harder to do I think).
* EJBs:
There are few valid reasons left for EJB to continue to have it's own component model. It increases the learning curve for new developers and has always proven to be a sticking point for Java EE adoption. It's best to gradually prune this or simply leave them be. As you suggested, let's separate the very useful EJB services from the component model and make them usable in managed beans as much as possible, likely as CDI "system" interceptors.
* JSF:
JSF managed beans and scopes are a set of endless confusion for Java EE developers. It's best to gradually prune these or simply leave them be and find ways to better merge JSF with CDI. It's also very embarrassing that things like JSF converters and filters don't support injection, etc.
* JAX-RS:
JAX-RS doesn't really need a lot of special treatment. You can probably place JAX-RS annotations on managed beans of various flavors. It's probably also OK i most cases for JAX-RS annotated managed beans to be injectable (into other components) as well. Some of this probably applies to JAX-WS as well.
* Servlet:
Similar to JAX-RS, Servlet related components probably don't need much special treatment either other than the fact that it makes little sense to make them injectable.
* JPA:
As I've mentioned in the past, we should seriously consider ways of making JPA entities just another managed bean with full access to things like injection. This is really pretty crucial if Java EE is to fully support DDD. Spring enables this today already and it is a source of competitive advantage.
* Bean Validation:
This is really the right model that other Java EE APIs could try and emulate. It has little in terms of it's own component model/life-cycle but just defines annotation based services/SPIs that can be placed on any candidate managed bean. We should see if bean validation can be even better incorporated to JAX-RS and the like.
I hope this makes sense and helps. I am happy to explain anything further or try to help formulate concrete proposals.
Mar 29, 2012 05:53:14 PM, jsr342-experts_at_javaee-spec.java.net wrote:
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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