Speakers: Mark Hapner (SPK-hapner) and Vlada Matena (SPK-vlada)

Moderator: Edward Ort (MDR-edort)

This is a moderated forum.

MDR-edort: Welcome to Java^TM Live. Our guests today are Mark Hapner and Vlada Matena, the authors of the Enterprise Java Beans^TM (EJB) spec 1.1 public draft. So let's begin. Who has the first question?


IgorL: According to EJB standard (V1.1 draft, section 18.1.2), Enterprise Java Beans are not allowed to manage threads. Can you recommend an alternative for implementing asynchronous tasks: For instance, archive middle tier data, produce data for reports, and so on?

SPK-vlada: For asynchronous messages, you can use JMS. For archiving, the EJB server should provide a mechanism to archive the data.


satishrudra: What is the basic difference between the data object in an object data base and an entity bean?

SPK-vlada: An entity bean defines the business methods that operate on data, it is not the data itself.


dlj: I want to use XML to track jobs involving histology and cytology samples. How do XML and EJB fit together?

SPK-vlada: You can use XML with EJB. You can use the ProjectX parser with JSP and servlets and EJB.


rickardoberg: If a servlet engine and an EJB container should live in same server, there is a need for both to access JNDI component environment settings. How will this interface be defined?

SPK-vlada: Both enterprise beans and servlets can use the Java Naming and Directory Interface^TM (JNDI) to access the environment entries. The entries are always in the java:comp/encontext implemented by the Container.


dgeary: How does a single user at home get started with EJB? Can you recommend any free EJB implementations and databases? When will Sun have a reference implementation?

SPK-hapner: The reference impl will be available for download soon after JavaOne. I believe there are other evaluation versions of EJB products available as well.


bengber: Do you envision people using EJB to support Internet Web applications or more for Intranet thin client apps?

SPK-vlada: EJB handles the reuseable business component part of a web application and JSP and servlets handle the presentation. This architecture is useful for both intranet and internet apps.


jtremlett: To follow on the question on entity beans, how do you see developing entity beans that interact with non-transactional applications. For example, how do we achieve transaction awareness?

SPK-vlada: You would use the NotSupported transaction attribute for the entity bean methods. You would have empty EJBLoad and EJBStore methods. Each business method would be a transaction to the back-end system. This works with systems like R/3.


dnelsen: Moderator, I've noticed, as have some of the others here, that the chat applet doesn't work unless we click Show Unformatted. Otherwise the chat screen just looks frozen on the 1st question. I am now showing unformatted and can see all the questions.

MDR-edort: This is a known bug in the applet. Sorry for the inconvenience. The good news is that a new tool for managing the chats is on its way, and we should be using it soon.


sramp: Remote Interface is the means by which clients call the methods on EJB, but EJB itself is not implementing the remote interface? Can you tell me how is that done?

SPK-vlada: The tools provided by the container generate a remote object that implements the RemoteInterface. This remote object delegates to the enterprise bean class instances.


IgorL: Question about container-managed entity beans. How can we manage Java attributes, that are not part of the entity object. Usually we would use these attributes to keep calculated values, once the entity object is loaded. It is our responsibility to calculate them again when the entity object is changed.

SPK-vlada: With CMP, you use the EJBLoad and EJBStore methods to calculate the values of the derived attributes. For example, you can use this for compression.


satishrudra: Are there any standards for developing EJB Container? If not, How is interoperability between different containers achieved?

SPK-vlada: In a later release of the EJB spec, we will define the interoperabilty between servers using CORBA protocols. So far, we have defined the application formats (this is RMI/IIOP) and transactions (his is OTS). We have to still define interoperable security and naming. We rely on the CORBA protocols for interoperability. We only specify which protocols to use.


sramp: I read in some article that CMP should be preferred over BMP. What is your comment on it, CMP vs. BMP?

SPK-vlada: We don't prefer one over the other. BMP gives the developer maximum flexibility in designing data access. CMP allows the deployer to develop the data access code at deployment time. Ideally, in the future we will be able to combine the advantages of both approaches.


rickardoberg: But the servlet engines and EJB container needs to access the JNDI namespace in order to setup the env. for EJB and servlet components. For this to work the JNDI namespace must have some interface for doing this initialization. When, how, will this be defined?

SPK-hapner: In many cases, the container implements its own part of the JNDI name space which is federated with the enterprise name space via JNDI.


jtremlett: To follow on entity beans wrapping non-transactional applications, how do we achieve rollback of transactions?

SPK-vlada: It does not seem to make sense that a business method of an entity bean demarcate transaction. However, the entity protocol is designed to allow the bean to take advantage of the EJBLoad and EJBStore method to cache data in a transaction.


jwg1: A comment/question regarding methods that may be called during afterCompletion(): We have a situation where we have a MSSQLServer stored-procedure interface to a third party server that we access via a session-bean/entity bean pair. We have no control over how these procedures are written. As a result we may not pass them a transaction context. We also have another entity bean that accesses an Oracle database over which we do have control. Both beans need to participate in the same transaction. The best we can do on the SQL server side is catch the afterCompletion() call and either commit or undo manually. However, EJB 1.1 says you can't call enterprise-bean methods in the afterCompletion() method. This puts us in a real bind—we now have no way of doing a compensating action should a rollback occur on the oracle entity bean. The best alternative would be if entity beans could implement something akin to SessionSynchronization and catch the afterCompletion() call themselves. Comments?

SPK-hapner: Dealing with non-transactional resources is difficult. EJB does not provide the ability to write a full compensation strategy for such resources. The only way to do this is to extend the container transaction manager to handle this special case. We are investigating other alternatives for EJB 2.0.


pperrone: Why use BMP at all? What does it provide you with other than what you can code yourself?

SPK-vlada: CMP has some limitations that makes it less suitable for some cases where BMP works. Also BMP does not mean that you have to code the data access. BMP includes the cases where the bean developer uses design-time data access components that ship with the entity bean.


mnf999: Comments on the portability of context propagation?? How does that REALLY work? No RMI/IIOP answer please ;-)

SPK-vlada: The current EJB spec does NOT define interoperability. When it does, it will be RMI/IIOP and the OMG Transaction Service. The OTS spec (its Java rendering is the JTS spec) defines how the multiple servers propagate the transaction context and how they perform the two phase commit. OTS works well with RMI/IIOP.


kchaganti: Is there any way a bean can call the client in an asynchronous manner.

SPK-hapner: The general answer is to use JMS messages when JMS is integrated as part of EJB 2.0. Some vendors will support asynch EJB calls for non-transactional EJBs that do not have a return value.


rickardoberg: Answer to jtremlett: as vlada hinted, it is possible for EJB containers to use caching to do "semi-transactions" in the case the backing store does not support true transactions. This will be able to handle rollbacks that are not connected to software or hardware failure (i.e. most of them).

SPK-vlada: Right.


Duffy: I am part of a development group that is just beginning to get our feet wet with EJB. We have begun with the online EJB tutorial using BEA's server. However we believe that BEA is too much for what we want to do. Are there any bare bones EJB servers out there? Also what is the status of Sun's reference implementation and what will it's licensing and pricing policy be?

SPK-hapner: The RI licensing details are still being resolved. An early access version will be available soon after JavaOne.


jthelin: Will the forthcoming "reference implementation" of EJB from Sun include a "reference implementation" of the JTS/JTA parts? If so, can you give some indication of how "full-featured" it will be; that is, will it support distributed transactions across multiple data sources?

SPK-vlada: The reference implementation of Java 2, Enterprise Edition will include support for distributed transactions. You can update multiple databases in a transaction.


sateeshr: What is Reference implemention of EJB??

SPK-vlada: There is no reference implementation of EJB per se. The reference implementation of the Java 2, EE will include the reference implementation of the EJB container. The compliance test suite for J2EE will test thoroughly for EJB compliance.


kchaganti: Is there any way the A bean can call back the Client?

SPK-hapner: Callbacks typically imply asynch invocation. This is best handled with JMS.


sramp: In the EJBhome interface we define the create method to return the Bean object. But its corresponding EJBCreate in the actual bean returns void. I am confused here. Can you comment on this?

SPK-vlada: IN EJB 1.1, the EJBCreate returns the primary key. With BMP, EJBCreate returns the primary key and the container creates an object reference that embeds the primary key. With CMP, the EJBCreate returns null. The container creates the primary key for the entity object. The return value of the EJBCreate method is defined to return the primary key to match the signature of the BMP style. This allows a CMP bean to be turned into a BMP bean by subclassing.


rickardoberg: Mark, but won't both servlets and EJB's access the env. through the "java:/comp/env" name? Because in that case there is no other way than to make the JNDI part separate of both EJB and servlet engine and have a well defined interface to it.

SPK-hapner: For J2EE, java:/comp/env is used by all components to access the environment set up for it at deployment. EJB 1.1 is one example of this. Each container will likely provide its own implementation of the 'java:' namespace.


flippant: Hi, I'm joining late so forgive me if this is either inappropriate or has already been covered. With regards to the 1.1 spec and JTA. I'm currently working on a container and I've been trying to figure out how my container is supposed to "know" about an existing transaction which is potentially in another VM. I suppose more to the point is "What is the recommended way to locate an *instance* of a JTA?"

SPK-vlada: The EJB spec does not prescribe how vendors should build containers. You can use any strategy that you wish.

MDR-edort: We're scheduled to end the chat at noon PDT. However the number of participants is high and the questions very good. So let's go until 10 after noon.


IgorL: Another question about container-managed entity beans. When we write code using the EJBActivate() method, how do we know when an entity object is already loaded (when an entity bean is assigned to an entity object from the cache, and call to EJBLoad() is not performed by the container).

SPK-vlada: The developer of an entity bean does not have to know this. It is the job of the container to manage the cache of the active instances and call the EJBActivate / EJBLoad / EJBStore / EJBPassivate methods at the right times.


ronenb1: According to a question about asynchronous tasks, how can we run asynchronous tasks without using additional APIs (without using JMS)? We would like to return to the client before we begin long-term processing on the server.

SPK-hapner: It is not possible to do asynch processing in an EJB with the facilities currently available. JMS is the mechanism we feel is best suited to this problem. We realize that this is an important facility.


rickardoberg: Duffy: See http://www.mgm-edv.de/ejbsig/ejbservers.html for a comprehensive list of available servers


rickardoberg: Let me try again ;-* servlets access java.// namespac* EJB's access java:// namespac* if EJB container implement java:// namespace the servlet engine can't access it in order to init and perform context switching* and the same if servlet engine implements java:/Conclusion: JNDI must be separate from both EJB container and servlet engine. Problem: How should the JNDI implementation be accessed by the EJB and servlet engines? How will this interface be defined? Is this clear enough?

SPK-vlada: The servlet runtime and the EJB runtime (runtime == container) is implemented by a J2EE platform vendor. The java:comp/env context is implemented as part of the platform. Since each component needs potentially a different set of values in the java:comp/env, the implementation of the context must be able to tell which component invokes the lookup call. Most platforms would use thread context to know which component is calling. I hope that I understood your question.


Misovec: Where can I load the latest Java Development Kit (JDK^TM) package. Is the package free?

MDR-edort: Your question isn't an EJB question, but I'll answer it. Go to the java.sun.com page and then select the APIs page. You can download from there. The JDK is free subject to licensing agreement.


flippant: With regards to JTA instances - but we need to play nice with other containers. I'm asking how *you* would do it.

SPK-vlada: I'd use RMI/IIOP and OTS. This is what many major vendors do. You will be able to interoperate with them. In a later release of the spec, we may *require* RMI/IIOP for compliance.


IgorL: Are there OLAP tools that works with EJB servers?

SPK-hapner: I'm not aware of specific tools for creating OLAP beans; however, EJB would be a good way to implement access to OLAP content or make OLAP requests.

MDR-edort: Well it's approaching 10 after noon. Our time is up. Thanks for an excellent session!

Signing off.

Last moderator (me) signing off. The forum is now unmoderated

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