Use EJBs in Webdynpro

Dear All,
We have the following scenareio to be achieved,
Use Database of the WAS Java engine and table creation using NWDS. - this can be done using data dictionary
Use EJBs Data Updation - we have created a EJB project. One ear project which can be deployed to j2ee engine.
In webdynpro we can able to create a java bean model. But when try execute this applicaiton, it leads to null pointer exception.
Any idea what could be the reason for this.
Thanks,

Thanks for your immediate reply.
Sharing reference: sap.com/QuickCarRentalEar.
Finished with warnings: development component 'Frames'/'local'/'LOKAL'/'0.2008.06.12.18.12.16'/'0':Caught exception during application startup from SAP J2EE Engine's deploy service:java.rmi.RemoteException: Error occurred while starting application local/Frames and wait. Reason: Clusterwide exception: server ID 13390350:com.sap.engine.services.deploy.container.DeploymentException: Clusterwide exception: Failed to prepare application ''local/Frames'' for startup. Reason=Clusterwide exception: Failed to start application ''local/Frames'': The referenced application ''sap.com/QucikCarRentalEar' can''t be started. Check the causing exception for details. Hint: Is the referenced application deployed correctly on the server?
Any inputs?...
Can any one throw some lights on internally how this webdynpro calls ejb and process completes.
Thanks..

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How to Retrive data from db using EJB in WebDynpro

hi...
i m using EJB's for backend connection in WebDynpro .in which i m able to store data in sapdb .for this i followed one tutorial which i have mentioned bellow which works perfectly.Now in the same Tutorial i want to retrive the data from database and disply it in WebDynpro
i .e i want to disply bonus when i give ssn no and also i want to disply all data in db.
Please help me as i m totaly new to this environment and also first time i m working on EJB.its very urgent
Thanks and Regards
Sonal<a href="https://www.sdn.sap.comhttp://www.sdn.sap.comhttp://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/docs/library/uuid/1f5f3366-0401-0010-d6b0-e85a49e93a5c">https://www.sdn.sap.comhttp://www.sdn.sap.comhttp://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/docs/library/uuid/1f5f3366-0401-0010-d6b0-e85a49e93a5c</a>

hi...
i m using EJB's for backend connection in WebDynpro .in which i m able to store data in sapdb .for this i followed one tutorial which i have mentioned bellow which works perfectly.Now in the same Tutorial i want to retrive the data from database and disply it in WebDynpro
i .e i want to disply bonus when i give ssn no and also i want to disply all data in db.
Please help me as i m totaly new to this environment and also first time i m working on EJB.its very urgent
Thanks and Regards
Sonal<a href="https://www.sdn.sap.comhttp://www.sdn.sap.comhttp://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/docs/library/uuid/1f5f3366-0401-0010-d6b0-e85a49e93a5c">https://www.sdn.sap.comhttp://www.sdn.sap.comhttp://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/docs/library/uuid/1f5f3366-0401-0010-d6b0-e85a49e93a5c</a>

Accessing database using EJBs in WebDynpro

Im using EJBs to access database...data is getting stored in the database...but i dnt know how to retrieve it...webDynpro is a totally new environment for me..it would be a great help if someone can help me solve my problem...
regards,
Sonal

- start with "import JavaBean model" (importing model)
- put model in Used Models
- bind model with controller (web dynpro components-> double click on <application name>
- bind view with controller (same vindow)
- apply template (table for reading data) in view
and you are redy for start.
Eq
your EJB is MyEJB, and there is some function myFunction() with Vector as return (Vector contains MyEJB objects)
now in controller put (eq in wdDoInit())
MyEJB myObject = new MyEJB()
wdContext.current<NodeName>.bind(myObject.myFunction());
good luck

Tutorial "Using EJBs in Web Dynpro Applications" ClassCastException

Hi,
I went through the tutorial "Using EJBS in WebDynpro Applications" step-by-step.
If I run the application I always get the following error message:
java.lang.ClassCastException:com.sap.engine.interfaces.cross.ObjectReferenceImpl
if I try to make a lookup to the SessionBean.
I use the following code:
InitialContext ctx = new InitialContext();
facadeHome = (FacadeHome) ctx.lookup("FacadeBean"); <- the error is related to this line
facade = facadeHome.create();
I have nothing more to provide to be more specifiv.
What did I forget to specify or to define?
Thanks for any help.

Hi holger,
try to do it like this
InitialContext ctx = new InitialContext();
Object obj = ctx.lookup("FacadeBean");//where FacadeBean is your jndi name
facadeHome = (FacadeHome)PortableRemoteObject.narrow (obj,FacadeHome.class);
facade = facadeHome.create();
hope this helps,
regards,
rahul.

Why to Use EJB rather then Direct Connection To Oracle Thru webDynpro?

Hi
Experts,
I want to know that why to use EJB to connect to oracle rather then direct connection via WebDynpro.
Please Give Me References to how to connect to oracle with EJB or WebDynpro.I want to tell you that i know JDBC,JAVA and basic web Dynpro.
Please Reply Me Dear Friends...ASAP.

EJB are better for a project beacuse the application is scalable, have less maintainence and have better performance.
Have you gone throght these:
Connect Oracle 9.2 DB to Web AS 6.40
web dynpro - database connection
web Dynpro application connecting to oracle
/people/ramesh.jandhyala/blog/2007/01/02/webdynpro-and-oracle-using-dtos
Regards,
Ashwani Kr Sharma

WebDynpro using EJBs

Hi,
Does anybody know how to connect to local database to WebDynpro using EJBs?
Is there any tutorial or gelp that makes use of different prespectives like Dictionary,Java,J2ee and WebDynpro?
I have gone through one tutorial Usings EJBs,but im facing some problem because i think there's something missings in that tutorail...
<a href="https://www.sdn.sap.comhttp://www.sdn.sap.comhttp://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/com.sap.km.cm.docs/library/webdynpro/using%20ejbs%20in%20web%20dynpro%20applications.pdf">https://www.sdn.sap.comhttp://www.sdn.sap.comhttp://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/com.sap.km.cm.docs/library/webdynpro/using%20ejbs%20in%20web%20dynpro%20applications.pdf</a>

From an architecture viewpoint I don't think it's a good idea to access EJBs from the J2EE presentation tier with SOAP, I'm afraid.
First, I'm assuming you have a local architecture anyway, that is, the presentation tier and the business (EJB) tier are not distributed. Using distributed access for a local architecture introduces considerable performance overhead. Using XML encoding introduces even more overhead.
Second, using web services technologies for access between J2EE tiers, you lose transportation of for example security and transaction contexts etc between the presentation tier and the business tier.
Rather, you should get access to your EJBs (it might be valuable to consider the session facade pattern btw) via JNDI. I don't know if WebDynpro allows for accessing the JNDI namespace, but as a workaround, you could do so from within a Servlet/JSP for example (workaround only !).
You might have the situation that exposing EJBs as web services makes sense to you anyway though, but then you are likely to have a distributed architecture and/or different client technologies accessing the business tier. Still, for a J2EE client accessing the EJB tier, I'd chose RMI/IIOP over SOAP/HTTP.
Matthias

Using EJBs in Web Dynpro

I have recently started to develop Web applications using the Web Dynpro framework. Coming from a pure J2EE world, I must admit that Web Dynpro has a few innovative features that I find interesting for user interface development. The use of component & view contexts, for example, is not unlike the ActionForms that one may find in a Struts application, but pushed a bit further. No complaints here.
What I do have some problems with is the whole CommandBean paradigm that is put forth by SAP (refer to the document <a href="https://www.sdn.sap.comhttp://www.sdn.sap.comhttp://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/com.sap.km.cm.docs/library/webdynpro/using%20ejbs%20in%20web%20dynpro%20applications.pdf">Using EJBs in Web Dynpro</a>).
I do understand the usefulness of defining a model that will be used to generate and eventually bind to Context data structures. That's fine. What I do object to is the use of a so-called CommandBean to play that role. Again, coming from a J2EE world, I am familiar with the BusinessDelegate pattern - which would typically be used by a client application to invoke business logic on the server side. I would propose that a better, cleaner way of integrating EJBs with the Web Dynpro framework would be to use a BusinessDelegate for invoking business logic, and importing a separate and distinct ModelBean (instead of a CommandBean) to be used for defining and binding to Context data.
I have built one Web Dynpro application thus far. Instead of using a CommandBean, I created a ModelBean that extends my business object DTO (Data Transfer Object) (which is quite appropriate for that role, given that it implements all the get & set methods that are required for the business data that I need to model). My Web Dynpro application also makes use of an independant BusinessDelegate that is packaged with my EJB DC - this is a standard best practice on J2EE projects. I have been asked by the people working with me to modify this architecture to bring it more in line with the SAP way of doing things. I am open-minded and willing to learn and accept new ways of thinking and doing things. However, I fail to understand the usefulness of merging structure and behaviour by resorting to CommandBeans:
- It violates the MVC paradigm by having one object (the CommandBean) serve as both model AND controller as far as the Web Dynpro application is concerned. The CommandBean is obviously a model - since it is literally imported as such into the Web Dynpro application. It is ALSO a controller from the Web Dynpro's application perspective, since all calls to the back-end go thru the CommandBean via one or more of its execute_xxx methods. In contrast, the use of a business delegate by the Web Dynpro application clearly separates the model (the CommandBean... or rather, a more suitably named ModelBean) from the controller (BusinessDelegate).
- Doesn't carry its own weight. In other words, I haven't yet been provided with any valid justification for going thru the extra effort of coding the CommandBean's execute methods. It's been proposed to me that it somehow serves as an abstraction layer between the Web Dynpro application and the business logic. I would argue that it is the BusinessDelegate's role to abstract away the back-end logic from clients. If one does have a BusinessDelegate available, I would argue there's no need to code execute methods in a separate CommandBean. To prove my point, I would simply point out that all of the CommandBean examples that I have seen so far, either in How-To documents, or in production code, all follow the same pattern....
CommandBean.execute_doSomething() calls BusinessDelegate.doSomething()
Not a heck of an "abstraction" layer... I would in fact argue that it is worse than useless. If some major change occurs in the business logic that requires changing the doSomething() operation, we expect of course to modify the BusinessDelegate. The Web Dynpro client will also presumably need to be modified - that's to be expected, and unavoidable. But then, we'll also need to go about and change the CommandBean's execute_doSomething() method - again, extra work for no apparent benefit. Adding and removing business methods has the same implication. All this for an layer that simply adds the prefix execute_ in front of all business method calls... Is this "abstraction layer" worth the cost of creating and maintaining it ??
- Unnecessarily complicates error handling. I have been told that for technical reasons, it is recommended that all exceptions thrown by the CommandBean be of type WDException or WDRuntimException. But what if the client application needs to react differently to different failure scenarios ? When I create a business object, I might wish to provide the user with an error messages if connection is lost to the backend, and with a different error message if an object already exists in the database with the same attributes. In order to do that, I will have to catch the WDException, extract the cause, and continue processing from there... possible, yes, but clearly less standard and more labor intensive than the classical try/catch mechanism.
To say nothing about the fact that SAP's own API documentation clearly states that applications using Web Dynpro can reference and catch WDExceptions, but THEY MUST NOT THROW OR EXTEND IT !
- Produces unnecessary DCs. Page 6 of the aforementioned document presents an architectural view of a Web Dynpro project that uses a CommandBean. Why an extra DC for the CommandBean ?? I created my ModelBean class right inside the Web Dynpro project (in the Package view). That, to me, is where this class should reside, because it is created for no other reason that to be used by this particular Web Dynpro application. What is the benefit of placing it in its own independant DC ?
- Not a typical application of the Command pattern. The well-documented command pattern (Design Patterns - Gang of Four) has been devised mainly to enable encapsulation of request as objects, thereby making it possible to:
- specify, queue and execute requests at different times
- decouple execution of a command from its invoker
- support undo operations
- support logging changes so that they can be reapplied in case of system crash making it possible to assemble commands into composite commands (macros), thereby structuring a system around high-level operations built on primitive operations.
None of this applies to the way the SAP CommandBeans are being used. Not that much of an issue to people new to J2EE and/or OO development... but quite confusing for those already familiar with the classic Command pattern.
At this point, I fail to understand the advantage of merging structure (model) and behaviour (execute methods) through the use of a unique CommandBean object. Am I missing something ?

Thanks for your reply and your suggestion. I have posted in the Web Dynpro Java forum... and suggest those wishing to participate in this thread to refer to the Web Dynpro Java forum.
As for your answer, I'm afraid it doesn't satisfy me.
Reuse is hardly an issue, since the CommandBean is specifically tailor-made for the Web Dynpro application that needs to use it. I could hardly imagine building another application that would just happen to have the exact same needs as far as data structure and processing is concerned...
As for the right Eclipse environment... the CommandBean is not an EJB artifact - it is an EJB client. The aforementioned tutorial in fact suggests creating it in the Java perspective.
But thanks anyway for your time and suggestion

Using EJBs in Web Dynpro Applications

I have recently started to develop Web applications using the Web Dynpro framework. Coming from a pure J2EE world, I must admit that Web Dynpro has a few innovative features that I find interesting for user interface development. The use of component & view contexts, for example, is not unlike the ActionForms that one may find in a Struts application, but pushed a bit further. No complaints here.
What I do have some problems with is the whole CommandBean paradigm that is put forth by SAP (refer to the document <a href="https://www.sdn.sap.comhttp://www.sdn.sap.comhttp://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/com.sap.km.cm.docs/library/webdynpro/using%20ejbs%20in%20web%20dynpro%20applications.pdf">Using EJBs in Web Dynpro Applications</a>).
I do understand the usefulness of defining a model that will be used to generate and eventually bind to Context data structures. That's fine. What I do object to is the use of a so-called CommandBean to play that role. Again, coming from a J2EE world, I am familiar with the BusinessDelegate pattern - which would typically be used by a client application to invoke business logic on the server side. I would propose that a better, cleaner way of integrating EJBs with the Web Dynpro framework would be to use a BusinessDelegate for invoking business logic, and importing a separate and distinct ModelBean (instead of a CommandBean) to be used for defining and binding to Context data.
I have built one Web Dynpro application thus far. Instead of using a CommandBean, I created a ModelBean that extends my business object DTO (Data Transfer Object) (which is quite appropriate for that role, given that it implements all the get & set methods that are required for the business data that I need to model). My Web Dynpro application also makes use of an independant BusinessDelegate that is packaged with my EJB DC - this is a standard best practice on J2EE projects. I have been asked by the people working with me to modify this architecture to bring it more in line with the SAP way of doing things. I am open-minded and willing to learn and accept new ways of thinking and doing things. However, I fail to understand the usefulness of merging structure and behaviour by resorting to CommandBeans:
- It violates the MVC paradigm by having one object (the CommandBean) serve as both model AND controller as far as the Web Dynpro application is concerned. The CommandBean is obviously a model - since it is literally imported as such into the Web Dynpro application. It is ALSO a controller from the Web Dynpro's application perspective, since all calls to the back-end go thru the CommandBean via one or more of its execute_xxx methods. In contrast, the use of a business delegate by the Web Dynpro application clearly separates the model (the CommandBean... or rather, a more suitably named ModelBean) from the controller (BusinessDelegate).
- Doesn't carry its own weight. In other words, I haven't yet been provided with any valid justification for going thru the extra effort of coding the CommandBean's execute methods. It's been proposed to me that it somehow serves as an abstraction layer between the Web Dynpro application and the business logic. I would argue that it is the BusinessDelegate's role to abstract away the back-end logic from clients. If one does have a BusinessDelegate available, I would argue there's no need to code execute methods in a separate CommandBean. To prove my point, I would simply point out that all of the CommandBean examples that I have seen so far, either in How-To documents, or in production code, all follow the same pattern....
CommandBean.execute_doSomething() calls BusinessDelegate.doSomething()
Not a heck of an "abstraction" layer... I would in fact argue that it is worse than useless. If some major change occurs in the business logic that requires changing the doSomething() operation, we expect of course to modify the BusinessDelegate. The Web Dynpro client will also presumably need to be modified - that's to be expected, and unavoidable. But then, we'll also need to go about and change the CommandBean's execute_doSomething() method - again, extra work for no apparent benefit. Adding and removing business methods has the same implication. All this for an layer that simply adds the prefix execute_ in front of all business method calls... Is this "abstraction layer" worth the cost of creating and maintaining it ??
- Unnecessarily complicates error handling. I have been told that for technical reasons, it is recommended that all exceptions thrown by the CommandBean be of type WDException or WDRuntimException. But what if the client application needs to react differently to different failure scenarios ? When I create a business object, I might wish to provide the user with an error messages if connection is lost to the backend, and with a different error message if an object already exists in the database with the same attributes. In order to do that, I will have to catch the WDException, extract the cause, and continue processing from there... possible, yes, but clearly less standard and more labor intensive than the classical try/catch mechanism.
To say nothing about the fact that SAP's own API documentation clearly states that applications using Web Dynpro can reference and catch WDExceptions, but THEY MUST NOT THROW OR EXTEND IT !
- Produces unnecessary DCs. Page 6 of the aforementioned document presents an architectural view of a Web Dynpro project that uses a CommandBean. Why an extra DC for the CommandBean ?? I created my ModelBean class right inside the Web Dynpro project (in the Package view). That, to me, is where this class should reside, because it is created for no other reason that to be used by this particular Web Dynpro application. What is the benefit of placing it in its own independant DC ?
- Not a typical application of the Command pattern. The well-documented command pattern (Design Patterns - Gang of Four) has been devised mainly to enable encapsulation of request as objects, thereby making it possible to:
- specify, queue and execute requests at different times
- decouple execution of a command from its invoker
- support undo operations
- support logging changes so that they can be reapplied in case of system crash making it possible to assemble commands into composite commands (macros), thereby structuring a system around high-level operations built on primitive operations.
None of this applies to the way the SAP CommandBeans are being used. Not that much of an issue to people new to J2EE and/or OO development... but quite confusing for those already familiar with the classic Command pattern.
At this point, I fail to understand the advantage of merging structure (model) and behaviour (execute methods) through the use of a unique CommandBean object. Am I missing something ?

Hi Romeo,
You would be disappointed, this reply ain't anywhere nearby to what you are talking about...
I wanted to mail you, but you have not mentioned your email in your profile.
I am really impressed by your flair for writing. It would be far better had you written a blog on this topic. Believe me, it would really be better. There is a much wider audience waiting out there to read your views rather than on the forums. This is what I believe. To top it, you would be rewarded for writing something like this from SDN. On the blogs too, people can comment and all, difference being there you would be rewarded by SDN, here people who reply to you would be rewarded by you. Doesn't make much a difference.
Anyways the ball is still in your court
As far as I am concerned, it has still not been much time since I have started working on Web Dynpro. So can't really comment on the issue...
Bye
Ankur

How to call jsp/ejb in webdynpro applications

Hi
Is It Possible to call jsp and EJB in webdynpro applications.If it is please let me know..
Regards
Chandra

Hi,
You can call JSp and serlvets using suspend and resume plugs
/people/bertram.ganz/blog/2006/07/03/web-dynpro-java-foundation--whats-new-in-sap-netweaver-2004s
http://help.sap.com/saphelp_nw04s/helpdata/en/42/bb8c6cc7131d67e10000000a1553f6/frameset.htm
For EJbs you can create a DTO and try to make use of the model import available in Webdynpro.
Regards
Ayyapparaj

Importing an EJB into WebDynpro

Hi all,
I am trying to import an existing stateless session bean into my webdynpro application.I have gone through the tutorials and other threads about bean model inthis forums.("https://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/com.sap.km.cm.docs/library/webas/webdynpro/using ejbs in web dynpro applications.pdf")but is it necessary to have another access layer as bean importer to acces the ejb.Since creating another layer is not suggestible in my scenario, I have tried importing the bean directly, it says "no beans available".
Also I would like to know how can i bind those values returned by business methods of bean to the UI elements.
Please suggest favourably.
KSK

Hi,
You can directly call the methods in the bean without using bean model
see this thread
Webdynpro and Oracle
Regards
Rohit

ClassCastException using EJB from a service

Hi all,
I developed a DeployService and currently I'm getting a ClassCastException while accessing the a EJB.
I put the lookup within a delegate which is also be used from a webDynpro application. With the WebDynpro App everything work properly, but if I call the delegate from the service a SAPClassCastException I thrown, when I cast the object to the home interface.
The coding is as follows:
 Properties props = new Properties();
 props.put(Context.PROVIDER_URL,"localhost:50004");
 props.put(Context.INITIAL_CONTEXT_FACTORY,
 "com.sap.engine.services.jndi.InitialContextFactoryImpl");
 context = new InitialContext(props);
 Object obj = context.lookup(jndiName);
 EJBHome ejb = EJBHomeFactory.getInstance().lookup(jndiName, ComponentHome.class);
 ComponentHome componentHome = (ComponentHome)ejb;
Thanks a lot for the help.
Falk

Hi Falk,
Hey just tell me that what is the EJBHome and ComponentHome and EJBHomeFactory in your coding.....
You can try the following code for the same.
Object obj =(Object) jndicontext.lookup("<Your JNDI name>");
TestEJBHome home = (TestEJBHome) javax.rmi.PortableRemoteObject.narrow(
 obj,
 TestEJBHome.class);
TestEJB hello = home.create();
Here, TestEJBHome is your Home interface of the EJB and TestEJB is your remote interface. Now you can use hello object to call your business methods of EJB.
Regards,
Bhavik

Thred Safety when Injecting an EJB into servlet using @EJB

Hi , i have read that
when EJBs were injected into servlets using @EJB it is said that there will be no Thread Safety here ??
Is this true.

Hi,
You can directly call the methods in the bean without using bean model
see this thread
Webdynpro and Oracle
Regards
Rohit

Using EJB as model

hi all,
i am new to Java Webdynpros.
I want to work on EJB as model.
Please can anyone give an example/ step by step using EJB as model in NWDS.
Regards,
Somya

Hi somya,
You Can use EJB Model in java Dynpros, Refer to these links you will find all The Process for Developing an application using EJB's.
[Importing Enterprise JavaBean (EJB) Models|http://help.sap.com/saphelp_nwce10/helpdata/en/45/dd45e4bc295595e10000000a1553f7/content.htm]
[Enterprise JavaBeans for Web Dynpro|https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/20b21892-c31c-2a10-f484-fcef1eaf8c4f]
[SAP NetWeaver J2EE Preview: Application Development with the EJB 3.0 Programming Model|https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/0914ef0d-0d01-0010-beb9-d85ef5a6188d]
I Hope This Information might be Helpful for you.
Regards,
Sharma.

How to use ejb methods

hi
i created 8 methods in ejb now
i want to use them in web dyn pro
but to display the response of every method i need to create table i.e in all 8 tables.
each table foe each response
is ther any other way out
can't i use single table for all

Hi Mitesh,
Sorry if I got you wrong, but if you are asking how to use an ejb in WebDynpro this thread may help you https://www.sdn.sap.com/sdn/collaboration.sdn?contenttype=url&content=http%3A//forums.sdn.sap.com/profile.jspa%3FuserID%3D635050 If your question is how to display the retrieved data on the screen, then you yourself will be best person to decide as no one else knows what data is being retrieved and how large they are.
Best Regards,
Nibu.

Exposing WebServices Using EJB Module

Hi,
I am facing problems in exposing Web Services using EJB module. But the same is working fine when i am using webDynpro to expose the services.
I am using the following code which gives error.
                                                                 IUser user = UMFactory.getUserFactory().getUserByLogonID(userID);                                    UWLContext uwlContext = null;
               IUWLService service = null;
               uwlContext = new UWLContext();
               service = UWLServiceHelper.findService();
               uwlContext.setUser(user);
               uwlContext.setLocale(user.getLocale());
any suggestion how to go about it??
Thanks
Utsav

Hello Utsav
I see that you have not been able to find a solution for this.
Can you provide some more information which may help the other SDN posters to assist you?
Thanks
Kenny

Use EJBs in Webdynpro

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