EJB Reviews 1993

Free download. Book file PDF easily for everyone and every device. You can download and read online EJB Reviews 1993 file PDF Book only if you are registered here. And also you can download or read online all Book PDF file that related with EJB Reviews 1993 book. Happy reading EJB Reviews 1993 Bookeveryone. Download file Free Book PDF EJB Reviews 1993 at Complete PDF Library. This Book have some digital formats such us :paperbook, ebook, kindle, epub, fb2 and another formats. Here is The CompletePDF Book Library. It's free to register here to get Book file PDF EJB Reviews 1993 Pocket Guide.

Probably they were so preocupied to erase the "dependent objects" blunder that they didn't have time to consider message beans more carefully. Now about local interfaces, certainly they are a progress, and I'm glad you're perfectly happy, but Entities have a long way to go before you can use them. Especially those relationships you mentioned and the new kid on the query langiages block. And from my point of view I don't see why would should stop at maximu 2 interfaces per EJB and we couldn't choose between 1 and n.

Like Microsoft had a very long time ago, and speaking about COM, some interfaces can be dedicated for collaboration between the bean and the infrastructure, just like in COM. And if we are in the same process the ORB should shortcircuit the call, and if not he should marshall. It's very simple. If you want protection for your parameters, you can vote for introducing the "const" keyword in future versions of Java. If you are perfectly happy with local interfaces, I'm ok with that, it's a good engineering compromise because they went on the wrong path with dependent objects and probably only had enough time to pick the easiest way at hand.

But it doesn't mean at all that they are the perfect solution.

What are EJBs Enterprise Java Beans?

Cheers, Costin. Cedric, By flaming I meant when you send somebody to do the reading and after that he can comeback to discussion.


  • EJB Reviews?
  • On Course.
  • 50 Years of EU Economic Dynamics: Integration, Financial Markets and Innovations.
  • Rover Mini Mayfair 1.3i.
  • Debating Governance: Authority, Steering, and Democracy: Authority, Steering and Democracy.
  • Salivary Glands: Development, Adaptations and Disease (Frontiers of Oral Biology, Vol. 14).

Now if you don't think dependent objects was a blunder, I'll tell you why they were a blunder. Exactly because they were dependent , then we had to species of animals: EJB and dependent objects, and things will local interface had only to be dependent of something.

EJB Reviews - Google Livres

Now we're back to a unitary and simpler approach where everything is an Entity, except that A BMP cannot be in a "relationship" with a CMP , relationships can be directional, and semantics of relationship assignment proclaimed side effects as the way to go, when they could have simply settled for raisng an exception when relationships semantics were broken. So we still have a way to go before EJB specification is something simple and unitary.

If there were "EJB experts" indeed, EJBs should have been something mature and robust after more than two years in the public. Maybe I'm missing something here.


  1. Bibliographic Information?
  2. Henry Sidgwick - Eye of the Universe: An Intellectual Biography?
  3. Bibliographic Information?
  4. If you want to make N different beans you will work very hard to make them the same logical object, and I'm not sure if it is at all possible. And it is something that we're missing in Java more then we miss any other particular JSR out there. Not to mention that you could also vote for the Generic type support, which is also something far more important for developers then any JSR we have at the moment.

    Interesting debate. I have just two points really. And I guess thats what the designers had in mind. This would give you the scalablity and distributed server farm architecture. And indeed Billy's system could be designed that way, with all the layers being called within a single EJB transaction. And in these scenarios, the order may well matter.

    Cites per any

    A create order must happen before an amend which must happen before a delete. Billy can make this synchronous by not using JMS and completeing an EJB create before an EJB amend before an EJB delete, but there may be reasons of proximity, or interfacing with existing systems, why these need to go in as feeds.

    I therefore agree that it is a shortcoming in the spec. So far, I've only used session beans, but I'd one day like to be able to purchase a simple off the shelf EJB workflow component that is application server and database independent. I don't want to buy a whole new Workflow server along with its own separate GUIs, database and message queuing applications that we have to support on top of the servers we currenlty use. This is where a single. Sure, its currently got performance problems, but thats where I'm hoping things will get beter, and even today, it'll probably be as fast as a monster of a workflow server, if not faster.

    The same problem appears again and again, with discussion servers, with time tracking applications, with CRM applications, helpdesk monitoring etc. It would be nice to not have to buy huge monster applications for each of these tasks. And thats where I see Entity beans being useful, certainly not on performance compared to coding it in session beans.

    In solving this type of problem, we have employed a J2EE workflow engine which runs inside our EJB server, so it does not add enormous deployment complexities on top of what we already have with J2EE. The workflow definition is used to define the order in which events must be processed. The workflow definition tool supports AND and OR as well, so you can do things like "the create event must happen first, followed by either a cancel event or a fulfillment event".

    Events are delivered into the workflow engine. The engine forwards them to specific instances of workflow, but they are not processed unless the workflow is in a state where it is ready for that event. If the workflow is not ready for that event, it is still waiting for one of the preceding events. Out of order events are held inside the WfMS and delivered to the workflow instance when it is ready for them. Billy, There are a lot of aspects to be considered and in some of those, the approach you are offering is flawed.

    I don't want to go too much into details as it would take much more space and time than I can afford, but I'll try to explain it briefly. It's pretty much established since Waldo et. First, if you are not convinced, I urge you to read this paper. Even though it's old ! This paper is hard to find, so I took the liberty to copy it to my Web site.

    Assuming we agree on the premises of this paper, it is clearly dangerous to expose only one interface that can transparently apply to local and remote objects. While it is something that most application servers have been providing as a non-standard feature for some time now including Weblogic , there are very clear gotchas associated with it, and developers need to be aware of them. It would be very easy for a bean provider to read the EJB specification carefully while overlooking the vendor's documentation, and find out the hard way that calls are made with pass-by-reference semantics.

    In that respect, Local interfaces are a definite progress since they separate both semantics very clearly.

    Another positive aspect of Local interfaces IMO is that they delineate more clearly the roles and responsibilities of relations. That being said, Local interfaces can also be viewed as a needless burden, forcing bean providers to freeze design choices very early on in the process of implementing their beans.

    What used to be a simple switch to activate in a deployment descriptor becomes now a radical change in the development process and forces more associated boiler-plate classes to be supplied as part of the bean. Time will tell if this issue matters that much, but my guess is that certain tools such as EJBGen ;- will alleviate this burden somehow. Okay, that was longer than I initially planned. Let me know if you'd be interested in a more in-depth analysis and I'll try to write up some kind of white paper expanding on these ideas.

    Hi Cedric, Finally, I'm provoking some debate here.. Good to hear from you. I never said objects should only have a single interface What I did say was use java beans for all local invocations and if it needs to be distributed, use a session bean as a fascade for it and any related beans. That's at least two interfaces. A local one and an optional remote one. The problem with my approach is that it is similar to the pre POA Corba world. Local calls short circuited the entire mechanism, i. As for relationships in EJB 2. Taking your argument that I may not care for switching vendor then what advantage did putting them in the spec server anyway given I have a reasonable implementation now in any case?

    Your sidebar on server state replication is exactly what I'm at. I have a messaging system where I cluster message containers. The container provides a proxy topic to subscribe to for the message bean and the container makes sure only m of n of the message beans are consuming work. The real topic does indeed carry both system and user messages, hence the proxy topic to filter system messages before the user code. The others are backups. The state is identical in all message beans on the same "Topic" otherwise the result is indeed chaos as you say.

    The container decides which m beans are active and I get a useful service from my J2EE server, i. Clustered in the sense, highly available rather than performance. Given BEA have already implemented this basically for handling HTTP Session failover and now stateful session beans, why not extend it to message beans?

    Why can't WebLogic's container pick a 'master' message bean and when it can't continue then promote another. My particular problem allowed non transactional semantics, BTW. Only user messages are received by the message bean. System messages are hidden by the container. The remaining nodes in the cluster then promote a shadow bean to master. The messages sent from the clients needs to be processed in order. No messages must be lost during failover but it's ok if a message is processed twice. For the moment, we're only concerned with handling app server failures, lets ignore the JMS component for now.

    Sorry to get a little off topic. I am interested in getting people's repsonse to the following. I do believe that Entity Beans do have some merit despite being non-portable. To do this I will have to write a fancy build procedure which will jar-up the appropriate CMP-type deployment descriptor.

    Розширений пошук

    I think that this is a 'bearable' task considering the marketing benefit. For this irksome task I get a good level of indirection between my database schema and my session beans the Entities provide this.

    Could they be faster - yes, could they be more portable - yes again. I've written quite a lot of BMP Entities and it was like pulling teeth trying to keep them in step with a constantly shifting db schema. People talk a lot about the non-portability of EJB but I think that they tend to consider portability of the bytecode too much. Just my 2c. Some doubts about local interface.

    Is there any other advantage besides pass by reference? Why not fix in the communication layer.. Also the spec says local interface requires the client and server colocated within the same VM Isn't that too low level? I agree remote call should not be treated transparently, but from the previous post, local interface also share the same container overhead as the remote interface.. If so,probably it is better to use normal java class in the first place?

    Do I miss something? Pramati's Server 3. Server 3. I planned in a project to group business use cases and place each group in an appropriate service session bean. Because I intend to offer exchangable business components being dynmically deployable I can do this only whith EJB-components, don't I? How could I build components of plain Java object and hot deploy these non EJB-component in an appserver. With Weblogic 6.

    If this is true then I can only dou this by wrapping these java components by fine grained session beans. So the design should provide services like yours but flexible local components which are called in the service layer. What is your opinion? Well, The session beans are coupled with the normal Java objects they wrap. You could deploy the java objects with a dummy session bean for example as a workaround, just package the classes in the ear file. Alternately, when the normal java business objects need to be updated then package them with the session beans wrapping them.

    Hi guys- A couple of points. I can't elaborate as to the exact date, but it's in lieu of upcoming product releases. I think we could debate Toby's suggestion for a long time. I think that would have been the easiest implementation. By forcing new developers to places methods in a component interface or local interface, it will cause them to provide additional thought into their design and what actually will be occurring at runtime. I suspect that developers will ultimately end up with better designs initially than using the DD specification approach.

    Of course, I know everyone will argue the fact that a component should ideally only have one business interface. Of course that's true and I'll just concede that point now. The more research that I do on local interfaces, however, the happier I get. I, too, am very excited about getting my hands on an implementation. Trust me in that it will be sooner than later.

    Tyler, Playing devils advocate here but whats the advantage of local interfaces over the approach I outlined. Develop your bean as a straight Java bean with a normal rich fine interface. If it needs to be accessible remotely then make a session bean that ties or delegates to it. This seems equivalent for me and I avoid the need to involve the J2EE descriptors etc. Any component interfaces will likely be a fascade wrapping the functionality of several 'local' ones.

    It seems like a poor fit, no, there doesn't appear to be a one to one mapping between local components and a distributed one. Will EJB 2. With "Local Interfaces" you will have the transactional control, object pooling, security, etc etc If you do not want that, then it may be better to use the approach that you outlined right? Well, I have that with the session bean fronting my normal bean in any case, no? Given a lot of parameters are cheap to copy then the cost of going through the container for security, pooling and transactions is still significant.

    I can turn off the copying for local objects in any case in WebSphere and as indicated by someone else in WebLogic and iPlanet. Maybe, Tyler can indicate some numbers for performance improvements but if this is the case then it appears to be hardly worth the effort. This overhead of going through the container is mostly still there for the majority of calls and especially if we're caching data then thats still going to be significant enough to probably stop you using them in any case if you're really worried about performance.

    Billy, I have the same concerns that you do. The specification to me is a little ambiguous as to whether or not local interface invocations can bypass transactional and security control. Obviously, by default, they'll have to have the same overhead as component interfaces -- I'm not fond of that at all. Billy, I think the architecture that you lined out was perfectly fine as well. At this stage of my understanding of local interfaces, I'm only making guesses as to whether or not they'll truly work. I want to now observe months of field implementation to get a better grasp of the limitations.

    Tyler, To tell you the truth, do we even need 6 months? Isn't it pretty obvious what the result will be? This is just due diligence but the answer is now clear. Overall, I'm now pretty underawed with EJB 2. It appears all that we will get from it now are MessageBeans and the ability to officially support pass by reference calls. Even the message beans are limiting. Whose idea was it to make them only stateless?

    Pretty short sighted. I dare anyone to respond and say that for in order messaging, stateless beans are more scalable, just stop, think about it, and smile. It's a big assumption in the spec that people will only ever want out of order messaging. What about financial customers implementing reliable trade feeds, price feeds reference data feeds, I could go on and on some people have said, I do go on and on but that's off topic.

    The EJB 2. It's hard to see the point of entity beans at all now. Get rid of them. Even products with competitive OR mappers BEA basically bugger portability by forcing everyone to use TopLinks API to really get the performance out of it so why both with entity beans at all. CMP is inherently unportable between implementations as so much of what's needed is obviously outside the specification.

    Anyway, sorry for the rant, good weekend Can anybody point me in the direction of a good example of how relationships are implemented in a EJB 1. Billy, Nice to see that this time you are being flamed for criticizing EJB : How's that for a change? Now to Cedric: If you want to build here a bibliography that's very kind of you, but you can start by assuming that people like Billy know what they are talking about.

    This is quite elementary; even if you want to flame people, at least you should be able to do it in a more subtle way. As to your points, you're funny. Billy is right here, probably we need to have statefull message beans and ordered messages also. Probably they were so preocupied to erase the "dependent objects" blunder that they didn't have time to consider message beans more carefully. Now about local interfaces, certainly they are a progress, and I'm glad you're perfectly happy, but Entities have a long way to go before you can use them.

    Especially those relationships you mentioned and the new kid on the query langiages block. And from my point of view I don't see why would should stop at maximu 2 interfaces per EJB and we couldn't choose between 1 and n. Like Microsoft had a very long time ago, and speaking about COM, some interfaces can be dedicated for collaboration between the bean and the infrastructure, just like in COM.

    And if we are in the same process the ORB should shortcircuit the call, and if not he should marshall. It's very simple. If you want protection for your parameters, you can vote for introducing the "const" keyword in future versions of Java. If you are perfectly happy with local interfaces, I'm ok with that, it's a good engineering compromise because they went on the wrong path with dependent objects and probably only had enough time to pick the easiest way at hand.

    But it doesn't mean at all that they are the perfect solution. Cheers, Costin. Cedric, By flaming I meant when you send somebody to do the reading and after that he can comeback to discussion. Now if you don't think dependent objects was a blunder, I'll tell you why they were a blunder. Exactly because they were dependent , then we had to species of animals: EJB and dependent objects, and things will local interface had only to be dependent of something. Now we're back to a unitary and simpler approach where everything is an Entity, except that A BMP cannot be in a "relationship" with a CMP , relationships can be directional, and semantics of relationship assignment proclaimed side effects as the way to go, when they could have simply settled for raisng an exception when relationships semantics were broken.

    So we still have a way to go before EJB specification is something simple and unitary. If there were "EJB experts" indeed, EJBs should have been something mature and robust after more than two years in the public. Maybe I'm missing something here. If you want to make N different beans you will work very hard to make them the same logical object, and I'm not sure if it is at all possible. And it is something that we're missing in Java more then we miss any other particular JSR out there.

    Not to mention that you could also vote for the Generic type support, which is also something far more important for developers then any JSR we have at the moment. Interesting debate. I have just two points really. And I guess thats what the designers had in mind. This would give you the scalablity and distributed server farm architecture. And indeed Billy's system could be designed that way, with all the layers being called within a single EJB transaction.

    And in these scenarios, the order may well matter. A create order must happen before an amend which must happen before a delete. Billy can make this synchronous by not using JMS and completeing an EJB create before an EJB amend before an EJB delete, but there may be reasons of proximity, or interfacing with existing systems, why these need to go in as feeds. I therefore agree that it is a shortcoming in the spec. So far, I've only used session beans, but I'd one day like to be able to purchase a simple off the shelf EJB workflow component that is application server and database independent.

    I don't want to buy a whole new Workflow server along with its own separate GUIs, database and message queuing applications that we have to support on top of the servers we currenlty use. This is where a single. Sure, its currently got performance problems, but thats where I'm hoping things will get beter, and even today, it'll probably be as fast as a monster of a workflow server, if not faster. The same problem appears again and again, with discussion servers, with time tracking applications, with CRM applications, helpdesk monitoring etc. It would be nice to not have to buy huge monster applications for each of these tasks.

    And thats where I see Entity beans being useful, certainly not on performance compared to coding it in session beans. In solving this type of problem, we have employed a J2EE workflow engine which runs inside our EJB server, so it does not add enormous deployment complexities on top of what we already have with J2EE. The workflow definition is used to define the order in which events must be processed. The workflow definition tool supports AND and OR as well, so you can do things like "the create event must happen first, followed by either a cancel event or a fulfillment event".

    http://police-risk-management.com/order/kids/kas-come-vedere-se.php

    EJB Reviews 1996

    Events are delivered into the workflow engine. The engine forwards them to specific instances of workflow, but they are not processed unless the workflow is in a state where it is ready for that event. If the workflow is not ready for that event, it is still waiting for one of the preceding events.