MVC + EJB?

I�m beginning to learn EJB and trying to get a clear picture of how EJBs fit into the Model View Controller design pattern. I currently design web applications as follows;
View � JSP
Controller � Servlets
Model � POJO in the Servlet Container.
Persistence � JDBC and Sun�s DAO pattern.
Using EJBs my thoughts are that my designs would need to change to;
View � JSP [no change]
Controller � Servlets [no change]
Model � data passed to Transfer Objects from EJB.
Persistence � EJB.
Is this correct?? If it is, does this mean there is now no business logic in my Model layer (it is all done at the Persistence/EJB layer?) Surely this can�t be right as this would mean the Model layer makes no business decisions and that EJBs effectively act as the Model AND Persistence layer?
I would appreciate your opinions.

View � JSP [no change]
Controller � Servlets [no change]
Model � data passed to Transfer Objects from EJB.
Persistence � EJB.
Is this correct?No. Code for the Model is implemented with EJB in the Business Tier.
Workflow is implemented using Session EJB and business entities are modelled with Entity EJB. The Integration Tier is where the relational database resides. The combination of the relational database, Entity EJB and EJB container handle the data storgage (persistence of the application).
Take note that there is no character "P" in the MVC acronym.
With EJB implementation you are free to change relational databases with ease and not have to alter any of the Entity EJB code. It is all handled declaratively with the Application Server. Check out Sun App Server and Weblogic.
If you want to save to file, you need to implement Data Access Object design pattern, so that no changes on business logic will be required.

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I would like to begin experimenting with JSP and the struts framework. I'm a java newbie but a relatively quick learner.
First, what products do I need to use struts/JSP ?
I have 9iAS standard edition release 1.0.2.1 and an oracle database std edition without the JVM installed. Do I need the JVM in the database ? Can JSP use a JVM outside the database ? Do I need enterprise edition ?
Do I need Jdevelopper 9i or can I learn to use JSP with simple tools (HTML editor) first ?
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Thanks a lot
You can reply to [email protected]

Thanks for your response.
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Thanks in advance.

Mvc structure in the ejb layer

hello
i am familiar with the mvc structure in the web layer,but i wonder how can i implement the mvc struction in the ejb layer.
i can use the stateless session bean as the controller,but in the web layer,i can use the url to identify the different request,and path information,but in the ejb container,it seem like there isn't such machanism,how can the controller(session bean) reforward the different request?where can i find the sample code of the sessin bean controller?is it included within the petstore?
thank you!

Hi,
If u have got the code for the same, please let me know.
Seetesh

Problems using JAAS with EJB 3.0 on JBoss 4.0.4-GA

Hello all,
I am trying to build a very simple JavaEE application with JAAS, but I getting mad.
I have an EAR packed with a WAR module an EJB JAR module and a JAR with other classes. Struts is the MVC framework and EJB 3.0 is been used.
First of all, I configured the "login-config.xml" file within /conf directory in JBoss, like this:
<application-policy name="exemplo1">
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          </login-module>
     </authentication>
</application-policy>Next I configured the "web.xml" file like this:
<security-constraint>
     <web-resource-collection>
          <web-resource-name>Restricted</web-resource-name>
          <description>Declarative security tests</description>
          <url-pattern>*.do</url-pattern>
     </web-resource-collection>
     <auth-constraint>
          <role-name>xxx</role-name>
     </auth-constraint>
     <user-data-constraint>
          <description>no description</description>
          <transport-guarantee>NONE</transport-guarantee>
     </user-data-constraint>
</security-constraint>
<login-config>
     <auth-method>FORM</auth-method>
     <realm-name>exemplo1</realm-name>
     <form-login-config>
          <form-login-page>/login.jsp</form-login-page>
          <form-error-page>/loginErro.jsp</form-error-page>
     </form-login-config>
</login-config>
<security-role>
     <description>Role xxx</description>
     <role-name>xxx</role-name>
</security-role>Notice that I am using the "xxx" role to protect the "*.do" URL pattern.
The "jboss-web.xml" is like this:
<?xml version="1.0"?>
<jboss-web>
     <security-domain>java:/jaas/exemplo1</security-domain>
</jboss-web>As it is, it works perfectly, which means, every time I try to access a "*.do" URL it verifies whether I am authenticated and have authroization or not. If not, the login page shows up.
Now I wanna to be able to also protect my EJBs.
My Stateless Session Bean is implemented as follow:
@RolesAllowed("yyy")
@Stateless(name="UserManagement")
public class UserManagementBean implements UserManagement {
     public void add(User user) {
}When I run all this, the container simply igoners the @RolesAllowed("yyy") annotation and allow the EJB execution.
If I add the "jboss.xml" file, like this:
<?xml version="1.0"?>
<jboss>
     <security-domain>java:/jaas/exemplo1</security-domain>
</jboss>I start getting this stack trace:
ERROR [UsersRolesLoginModule] Failed to load users/passwords/role files
java.io.IOException: No properties file: users.properties or defaults: defaultUsers.properties found
at org.jboss.security.auth.spi.Util.loadProperties(Util.java:313)
at org.jboss.security.auth.spi.UsersRolesLoginModule.loadUsers(UsersRolesLoginModule.java:186)
at org.jboss.security.auth.spi.UsersRolesLoginModule.createUsers(UsersRolesLoginModule.java:200)
at org.jboss.security.auth.spi.UsersRolesLoginModule.initialize(UsersRolesLoginModule.java:127)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
... Am I missing something? What do I have to do to get JAAS working fine with my EJBs? Do I have to also configure and/or provide "ejb-jar.xml" ???
Thanks
Daniel

Using @SecurityDomain("exemplo1") in my EJB and NOT providing jboss.xml, it works.
@SecurityDomain("exemplo1")
@RolesAllowed("yyy")
@Stateless(name="UserManagement")
public class UserManagementBean implements UserManagement {
public void add(User user) {
}Damn! This is some serious shit... I don�t want to configure this in every single EJB.
EJB 3.0 is nice, but some small trivial details like this and others, that was forgotten by Sun, piss me off!

MVC Design Help, Single Servlet, How do I access the Model and DB

Hi all. New here and looking for some help.
I am currently writing a website that allows the creation of users, that may upload articles and post comments on articles. Im trying to develop using MVC. I have a single controller servlet that processes POST actions throughout the site (eg. InsertArticle, DeleteArticle, ModifyArticle, etc..)
Now my problem is, just how do I retrieve the articles from the database? .. for example, if I load up a page http://localhost/articles.jsp which should display all the articles currently in the site.. I would have a function say getAllArticles() which should return a collection of all the articles. I can then iterate through the articles in the jsp page.
I am trying to use <jsp:useBean...etc.> BUT.. my articles bean constructor takes a databaseconnection object as a parameter. If I use useBean I cant pass the databaseconnection object to the bean and I get an error because it cannot create the bean.
Any help on this would be appreciated as well as any tutorial links. I also looked at the petstore blueprint program on the sun website, but that program has me completely lost with all the xml. I would prefer not to use custom tags or struts for now. I would like to keep it simple with snippets of java code in the jsp pages for data retrieval and display while keeping all the business logic in the beans of the model. I would also like to keep this relatively secure. I am developing using Oracle Jdeveloper 10g.
Thanks
Jazz

Hey steve, thanks for that.. but thats exactly what i
dont want to do. I also realize that ive been writing
the ejb's incorrectly to begin with and have begun to
rewrite them. However maybe I can make it easier..
what im trying to do is precisely what is in this
diagram..
http://gsraj.tripod.com/jsp/jsp.html
the problem im having is where it passes data back to
the jsp page.. entity beans cant (or shouldnt?) be
accessed directly from jsp pages.. which means i
create a session bean which interacts with the entity
bean and can return information to the jsp page.. i
understand what i have to do.. i just dont know how to
do it.. been searching for google for tutorials and
etc.. this site is the closest ive come but .. as you
can see it says "more to come" ..
thanks again guys really appreciate itAhhh. EJBs. Enterprise Java Beans and JavaBeans are two completely different beasts. I know nothing about EJBs, except:
1) They are much harder to use (and serve a different purpose I assume) then JavaBeans
2) Tomcat (the server I use) doesn't support them.
Sorry I can't be of more help.

How can i use tag library in the mvc?

hello
in some tag libraris such as jakarta tag library and jrun tag library,there is database
access tag, it provide convenient function to access database from jsp page,but i wonder how can i use such a tag within MVC architecture.
as we know,in MVC architecture,all requests from the jsp pages are submit to the controller servlet,then the controller manipulate ejb to access database,it don't allow the database access from the jsp page.
who can tell me how can i combine the tag library with mvc architecture appropriately?
thank you!

You can't! If you decide to limit the JSP to be part of the View component, obviously you should not include tags that directly access the database. If the strict MVC architecture is less important to you, then the tags can save coding time. It's your choice.

MVC model in Web systems and applications

MVC model in Web systems and applications
Object-oriented design model is experience, MVC idea is a user interface for the original. This article discusses how the major application areas in the new Web design patterns and the use of MVC framework. The article first introduced the concept of design patterns and characteristics, and MVC architecture design concepts and analysis of the MVC framework contains several key models. Based on the characteristics of Web applications on how to use patterns and MVC framework made some design ideas.??
1. Introduction
1.1 design model
Object-oriented technology and the emergence of software applications has greatly enhanced the trusted and software quality. Object-oriented programming than previous models to various programming simple and efficient, but the object-oriented design methodology than the previous design methods to complex and much more skill, a good design should be both on the issue of gender, but also to take full account of the problems and needs sufficient interoperability. In the past 10 years, people in the object-oriented technology and the practical application of research to explore certain issues in relation to the creation of a number of good solutions, the so-called object-oriented design patterns. Object-oriented technology is one of the purposes of enhancing the software trusted, and to design model, design programmes in important positions from a deeper sense of meaning and essence embodies trusted. There are many people in the design model definition, which cited Christopher Alexander is the largest design model definition : Each design model is a tripartite rule, which expresses a contextual environment (Context), a problem and a solution. Design models generally following basic elements : model name, the purpose solution effect 1995-1998 code and related design models. There are several classifications design patterns can be divided into a model based on the purpose (Creational), structural type (Structural) and the type of behaviour (Behavioral) three. It is mainly used in the creation of a model-based object model-based structure to deal primarily with the category or combination of objects, used to describe behavior-based model is the main target for the category or how stress and how to allocate responsibilities. Design patterns can be divided into categories based on the scope and target mode model type model dealing with the relationship between the categories and sub-categories, these relations through the establishment of succession in Translation moment to be finalized, are static. Model is targeted at addressing the relationship between the moment of change these relations in the operation, more dynamic. Model features : through the experience acquired in a structured format to write down, avoid encountering the same problems on the first design, exist in different abstract level, in continuous improvement, can be trusted artificial product for the design and best practice in the world to be combined to address larger issues.
1.2 MVC framework
MVC was first used in a user interface Smalltalk-80 China. M representative models Model, representatives maps View V, C representatives controller Controller. MVC trusted code with the aim of increasing the rate of data reduction expressed, the data describing the operation and application coupled degrees. Also makes software Keweihuxing, restorative, expansionary, flexibility and packaging of greatly enhanced. Single-user applications are usually incident-driven user interface to the organizational structure. Staff development tool with an interface painting of a user interface interface code based on user input and then prepare to implement the corresponding moves, many interactive development environment encouraged to do so, because it emphasizes first and then a functional interface. Some software design model is the strategy that will be fixed before the code into the regular system of the final. Result is that the procedures and organizations around the user interface elements in the user interface elements of those moves, data storage, applications and functions of the code is used to indicate the way intertwined. In single-user system code structure can be so, because the system will not demand frequent changes. But for a large system such as large Web systems, or e-commerce systems to be applied. Model by incorporating data from a variety of access and control data can be separated to improve distributed system design. MVC design pattern is composed of three parts. Model is the application object, no user interface. Type in the screen showing that it represents the flow of data users. Controller user interface definition response to user input, the users responsible for the action against the Model into operation. Model View data updated to reflect the adoption of data changes.
2. MVC design pattern,
An MVC framework for the design of the system includes many models, but with MVC is most closely related to the following three models : Observer, Cambridge and Strategy.
2.1 Observer models
MVC through the use of purchase / notification form and the separation of the Model View. View to ensure that their content accurately reflected Model and state. Once Model content changes, there must be a mechanism to allow notification to the relevant Model View, View can be made relevant at the appropriate time updating of data. This design is also more general problems can be solved, the target separation, making a change to the target audience affect others, which targets those who do not know the details of the object being affected. This is described as Observer in the design model. Model type : Observer model is the object-oriented model, it is behaviour-based model. Model purposes : definition of hierarchical dependence relations between objects, or when a target value of the state change, all its dependent relationship with the object are notified and automatically updated. There are a variety of data may show a way, in different ways and may also show. When a way through a changed data, then the other should be able to show immediately that the data change and do accordingly.
Effect :
1. Abstract coupling. I only know that it has a target audience of some observers, the observers met each abstract Observer category simple interface, does not know their specific affiliation categories. This makes the coupling between goals and observers smallest and abstract.
2. Support radio communications. Needless to notify designated observers goals, how to deal with the observer informed decisions.
3. Possible accidents updated. We update logic, avoiding mistakes updated.
2.2 Faculty model
MVC is an important feature of View can nest. Nest can be used for any type of combination of local maps available, but also management of type nest. This thinking reflects the type and mix of components will be equal treatment design. This object-oriented design ideas in the area of Cambridge has been described as a design model. Model types : Cambridge model is the object-oriented model, it is also the structure type model. Model purpose : to target portfolio into tree structures to express "part-whole" level structure. Prepared for the use and combination of individual target audiences with the use of consistency.
Effect :
1. Definition of a target portfolio includes simple objects and the structure of the category level. Simple objects may be complex combinations of objects, and can be targeted portfolio mix. This customer-code used in the target areas can use simple combinations target.
2. Simplify customer-code. Needless to know their customers - a mix of target audiences is a simple target or can use these items in a consistent manner.
3. Easier to add new types of components. New components can easily be changed to a combination of customer-targeted codes.
2.3 Strategy model
Another important characteristic is the MVC can not change the View of changes View response to user input. This often requires a change in response to the logic of the system is very important. MVC to respond to the logic involved in the Controller. Controller of a category level structure could easily change to the original Controller appropriate, a new Controller. View Controller son used to achieve a specific example of such a response strategy. To achieve different response strategy, as long as examples of the use of different types of replacement will Controller. Also in the running time by changing the View Controller for users to change View of response strategies. This View-Controller relationship was described as an example of Strategy design pattern. Model types : Strategy model is the object-oriented model, it is behaviour-based model. Model purposes : definition of a series of algorithms, and their packaging, and ensure that they can replace each other, making algorithms can independently use its customer-change.
Effect :
1. Strategy category levels for Context definition of the relevant algorithms can be trusted or behaviour.
2. Alternative methods of succession. If the direct successor Context, with different acts will be added Context act, the realization of which would algorithm mixed up with Context, Context hard to preserve and expand, but can not dynamically changing algorithms. Will be enclosed in a separate Strategy category algorithms to enable algorithm independent Context change easily cut over expansion.
3. Can provide the same acts different date.
4. Strategy-must understand what customers between different.
5. Context and Strategy communications between costs.
6. An increase in the number of targets.
3. MVC in Web application system
Now some of the distributed systems such as Web-based B2B e-commerce system, suitable for use MVC framework. Through analysis from the perspective of high-level applications can be a target divided into three categories. Category is shown for the target audience consists of a group of commercial rules and data, there is a category that is receiving requests to control commercial target to complete the request. These applications often need to change is shown, such as web style, color, but also need to demonstrate the contents of the display. And the business rules and data to be relatively stable. Therefore, said that the frequent need to change the View objects that the business rules and data model to be relatively stable target, and that the control of the Controller is the most stable. When the system is usually issued after the View objects by artists, designers or HTML/JSP system managers to manage. Controller target applications development personnel from the development and implementation of rules for commercial and business development personnel from the target data, database managers and experts in the field of common completed. Show in Web?? or customers - control logic can be Servlet or JSP, dynamically generated Html. Generally used Servlet better than using JSP. JSP will be better with the Html code of separate codes for page designers and developers of separation efficiency. Servlet and JSP can complete all complete functions, actually JSP eventually converted into a Servlet. And control of the target system exists in every level, the coordination of cross-layer moves. Contain business rules and data objects exist in the EJB layer (EJB-centred model) or Web?? (Web-centred model).
3.1 View in the Web application system
View of the system shows that it fully exist in Web??. General by JSP, Java Bean and Custom Tag. JSP can generate dynamic web content using Java Custom Tag easier Bean, but it can show the logic of packaging, and more conducive to modular trusted. Some well-designed in a number of JSP Custom Tag can even be used in different system duplication. Model for control of JSP and Java Bean objects. JSP through Java Bean objects to retrieve the data model, the Model and Controller object is responsible for updating the data on Java Bean. In general, can we devise all possible screen that users can see all the elements of the system. Based on these elements, to identify the public part of passive components and dynamics. Can consider the use of templates means to separate the content generated JSP public, also need to change their generation Html or JSP from a JSP templates to dynamically introduce these different parts (include methods). Another issue to consider is screen option, when dealing with End users request template automatically available to show that the concern that users must know what is the screen components. So can consider all screens on the definition of a centralized document, such as a document or text document java. Taking into account the possibility of changes in future document definition screens, the best use of text documents such as a XML document, so future changes to the recompilation. According to the URL and user input parameters to shine upon the results of a screen, of course, likely to be made on the basis of the outcome of the implementation of actions to choose different results screen. Therefore, the need for a request for matching resources with document (XML), if a URL request several different results, it must specify in the document need to control the flow (a controller object), as well as the corresponding screen different flows.
3.2 Model in the Web application system
Model objects represent business rules and business data exist in EJB layer and Web??. In J2EE norms, the system needs some data stored in the database, such as user account information (account model), the company's data (company model), some not recorded in the database. If a user browsing the current catalogue (catalog model), the contents of his shopping (shopping cart model). Which one of these models exist in the data according to their life cycle and scope to decide. In Web?? a HttpSession and ServletContext and Java Bean objects to store data in the EJB layer is a data storage and logic EJB to. Web?? the Java Bean objects stored in the model layer model of the EJB object data copy. Because there are many different EJB tier model targets, so Web?? through a ModelManager to control the EJB layer object model in ModelManger background model can be used for packaging methods. In the EJB layer and the rules have all the data into EJB model is inappropriate. If the database can visit the Dao object model into objects. Dao can be encapsulated and the specific details of the database in the world, if we can write a different table, a number of databases, or even multiple databases. If the orders can be a model for OrderDAO, it may have to deal with Order table, table and OrderItemLines OrderStatus table. Value can also consider the use of targets. Value can be a target of securing long-range targets, because every time the remote object attributes could be a long-range redeployment process will consume network resources. EJB objects in the distance can be used instead target. In the distance, one-time items to be targeted instead of the value of all attributes.
3.3 Controller in Web application system
Coordination with the Model View Controller object to the request of users into the system to identify incidents. In Web?? generally a MainServlet (or Main.jsp), and receiving all requests, it can use screen flow management devices (ScreenFlowManger) decided next screen. There is a general request processors RequestProcessor contains all requests are needed to be done to deal with logic, such as the request translated into system events (RequestToEvent). Acting processors usually also includes a request for ClientControlWebImpl, it is logical to deal with the EJB layer in Web?? Acting. In EJB layer, a layer for EJB tier Web ClientController provide the CD visit. Another StateMachine used to create and delete ejb handle Web?? sent to the incident. Controller Another important function is synchronous View and Model data. ModelManger contained in a ModelUpdateManger, it puts events into a Model System assembly that all the needs of synchronous Model, and then notify Listeners do synchronous operation.
4. Concluding remarks
In recent years, with the Internet technology development and the emergence of new business models, the Web is based on a large number of applications. On how to design these systems architecture, and gradually there has been some convergence of opinion, the most important point is that its structure should be rational in the open. Demand than ever faster development of technology and design concepts, systems for the future, the cost of upgrading the smallest, research software systems architecture still very useful and necessary.

Bravo. And your point is?

I need a clarification : Can I use EJBs instead of helper classes for better performance and less network traffic?

My application was designed based on MVC Architecture. But I made some changes to HMV base on my requirements. Servlet invoke helper classes, helper class uses EJBs to communicate with the database. Jsps also uses EJBs to backtrack the results.
I have two EJBs(Stateless), one Servlet, nearly 70 helperclasses, and nearly 800 jsps. Servlet acts as Controler and all database transactions done through EJBs only. Helper classes are having business logic. Based on the request relevant helper classed is invoked by the Servlet, and all database transactions are done through EJBs. Session scope is 'Page' only.
Now I am planning to use EJBs(for business logic) instead on Helper Classes. But before going to do that I need some clarification regarding Network traffic and for better usage of Container resources.
Please suggest me which method (is Helper classes or Using EJBs) is perferable
1) to get better performance and.
2) for less network traffic
3) for better container resource utilization
I thought if I use EJBs, then the network traffic will increase. Because every time it make a remote call to EJBs.
Please give detailed explanation.
thank you,
sudheer

<i>Please suggest me which method (is Helper classes or Using EJBs) is perferable :
1) to get better performance</i>
EJB's have quite a lot of overhead associated with them to support transactions and remoteability. A non-EJB helper class will almost always outperform an EJB. Often considerably. If you plan on making your 70 helper classes EJB's you should expect to see a dramatic decrease in maximum throughput.
<i>2) for less network traffic</i>
There should be no difference. Both architectures will probably make the exact same JDBC calls from the RDBMS's perspective. And since the EJB's and JSP's are co-located there won't be any other additional overhead there either. (You are co-locating your JSP's and EJB's, aren't you?)
<i>3) for better container resource utilization</i>
Again, the EJB version will consume a lot more container resources.

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:
- <b>It violates the MVC paradigm</b> 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).
- <b>Doesn't carry its own weight.</b> 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 ??
- <b>Unnecessarily complicates error handling</b>. 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 !
- <b>Produces unnecessary DCs</b>. 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 ?
- <b>Not a typical application of the Command pattern</b>. 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:
- <b>It violates the MVC paradigm</b> 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).
- <b>Doesn't carry its own weight</b>. 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 ??
- <b>Unnecessarily complicates error handling</b>. 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 !
- <b>Produces unnecessary DCs</b>. 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 ?
- <b>Not a typical application of the Command pattern</b>. 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

Best way to call EJB - Servlet or Tag Library

Hi,
What is the best way to call an EJB from a JSP? We are using Weblogic 7.0(moving to 8.1 beta). WE have a form on a JSP that needs to get data from an EJB. Our flow goes from JSP --> Controller servlet or tag library -->EJB "Bean" Controller ---> EJB. The specfic EJB we need to populate drop downs and fields will be called by a bean controller. Is it better to call the bean controller using a tag library in the jsp or go to the controller servlet to get the data? If servlet is the answer, where do I lookup the EJB Home and call the create from within the servlet? Any help would be greatly appreciated!!
Thanks!

IMO, if you are following some design patterns, like the MVC framework, the best thing is to populate the model(entities that contain the business data) and call the respective getXX methods from the model on the JSP page. The reason for doing so is to keep JSP pages away from any other work other than to just display the business data contained in the respective business entities.
The model can be populated in the servlet and either set in the request or session attribute as per the requirement.
The EJB can be looked up in the servlet as and when required. I would suggest to make use of the Service Locator Pattern to do a look up for the EJB Remote Interface and accordingly make the business calls.
Hopefully this answers some of your questions.

Connecting to Remote EJB from Servlet in same application

Please help!
I was able to connect to SessionBeans and EJB from my sample java client in OCJ4 but when I try to do same thing from my web application using servlets, I get the below NullPointerException error.
The JNDI lookup works fine using java client but difficult from a servlet.
I am sure there is something I am missing.
Thanks
This is what I do in the servlet:
public void init() throws ServletException, NamingException, CreateException, RemoteException
Context jndiContext = getInitialContext();
SessionCartEJBHome home = (SessionCartEJBHome)jndiContext.lookup("SessionCartEJBBean");
sessionEJB = null;
try{
sessionEJB = (SessionCartEJB) home.create();
}catch (Exception e)
e.printStackTrace();
private static Context getInitialContext() throws NamingException
Hashtable env = new Hashtable();
// Standalone OC4J connection details
env.put(Context.INITIAL_CONTEXT_FACTORY, "com.evermind.server.rmi.RMIInitialContextFactory");
env.put(Context.SECURITY_PRINCIPAL, "admin");
env.put(Context.SECURITY_CREDENTIALS, "admin");
env.put(Context.PROVIDER_URL, "ormi://Princeton/ejb1");
return new InitialContext(env);
And when I call the following procedure, it blow up at the line sessionEJB.getLineItem(new Long(1304));
sessionEJB is a class variable.
void processCatalogPage(HttpServletRequest request,
HttpServletResponse response,
ActionMapping mapping,
HttpSession session
throws ServletException, IOException , Exception, FinderException{
try {
ActionForward actFor = null;
String itemId = request.getParameter("id");
if ( itemId != null ) {
String[] itemIds = new String[1];
itemIds[0] = itemId;
sessionEJB.getLineItem(new Long(1304));
actFor = mapping.findForward("catalog");
return (mapping.findForward("success"));
} catch (Exception ex)
ex.printStackTrace();
System.err.println(ex.toString());
throw new EJBException(ex.toString());
04/12/11 23:45:24 java.lang.NullPointerException
04/12/11 23:45:24 at com.alashoofi.Cart.processCatalogPage(Cart.java:187)
04/12/11 23:45:24 at com.alashoofi.Cart.execute(Cart.java:86)
04/12/11 23:45:24 at org.apache.struts.action.RequestProcessor.processActi
onPerform(RequestProcessor.java:484)
04/12/11 23:45:24 at org.apache.struts.action.RequestProcessor.process(Req
uestProcessor.java:274)
04/12/11 23:45:24 at org.apache.struts.action.ActionServlet.process(Action
Servlet.java:1482)
04/12/11 23:45:24 at org.apache.struts.action.ActionServlet.doGet(ActionSe
rvlet.java:507)
04/12/11 23:45:24 at javax.servlet.http.HttpServlet.service(HttpServlet.ja
va:740)
04/12/11 23:45:24 at javax.servlet.http.HttpServlet.service(HttpServlet.ja
va:853)
04/12/11 23:45:24 at com.evermind.server.http.ServletRequestDispatcher.inv
oke(ServletRequestDispatcher.java:765)
04/12/11 23:45:24 at com.evermind.server.http.ServletRequestDispatcher.for
wardInternal(ServletRequestDispatcher.java:317)
04/12/11 23:45:24 at com.evermind.server.http.HttpRequestHandler.processRe
quest(HttpRequestHandler.java:790)
04/12/11 23:45:24 at com.evermind.server.http.HttpRequestHandler.run(HttpR
equestHandler.java:270)
04/12/11 23:45:24 at com.evermind.server.http.HttpRequestHandler.run(HttpR
equestHandler.java:112)
04/12/11 23:45:24 at com.evermind.util.ReleasableResourcePooledExecutor$My
Worker.run(ReleasableResourcePooledExecutor.java:192)
04/12/11 23:45:24 at java.lang.Thread.run(Thread.java:534)
04/12/11 23:45:24 java.lang.NullPointerException
Dec 11, 2004 11:45:24 PM org.apache.struts.action.RequestProcessor processExcept
ion
WARNING: Unhandled Exception thrown: class javax.ejb.EJBException

Avi,
Thanks for your response. I am actually returning a new InitialContext in a function call in the servlet. What I have noticed though is that JDeveloper creates two ear files for the application. One for the ejbs called ejb1.ear and another for the web files webapp1.ear. These are located in the applications subdirectory in OC4J directory.
I know I have two projects in the application, model and viewController. I am just trying to follow the MVC pattern.
In short, I don't think the web and the ejbs are in same ear file. I made the web project depend on the ejbs though. There is an option to set such. I don't know how to tell JDeveloper to put them all in one ear file.
I will appreciate any suggestion.
Thanks
Matilda

Oracle10g Jdbc Drivers issue with EJB on Weblogic 7

Hi there,
We are facing a critical issue on production environment related to Oracle jdbc drivers.
We have a J2EE application with swing client. We are using MVC framework where client calls go to stateless session bean which redirect it to specific POJO which then uses Entity Beans for persistence.
We have following environment.
JDK1.4.2, Weblogic 7 with SP5, Oracle10g on AIX 5.2
Now the problem is that we were using Oracle 8 jdbc driver classes12.zip for our application. Everything was working smoothly. Recently we moved our weblogic and oracle Servers machines locations, after that movement we started to get an exception when weblogic initializing connection pool that makes connection to a different oracle10g database. Oracle supports ask us to upgrade the jdbc driver. So we moved to 10g driver ojdbc14.jar but during testing one functionality is failing with a exception where rest of application seems to be working fine. The exception occurs when we try to post a record and during the creation of a child entity bean the transactions rollback for some unknown reasons. Using the old oracle8 classes12.zip driver the same code working fine again. We have also tried the classes12.zip driver of Oracle10g but error persist. I have checked the code and deployment descriptors but they seems fine. If i comment the creation of that particular entity bean the parent bean get created successfully and transaction commit successfully. Please also note that we have not created any relation b/w both entity beans not even in the database. They both are sort of independent.
Can any one having any idea why Oracle10g driver not working or what might be the problem with our configuration. Any help will be highly appreciated. Please see the Exception below.
<Jan 29, 2008 6:03:10 PM PKT> <Info> <EJB> <010036> <Exception from ejbStore: javax.ejb.NoSuchEntityException: Instance
of bean 'SecurityRatingHistoryPost' with primary key 'com.cdc.fms.server.setup.security.ratinghistory.SecurityRatingHist
oryEntityPK@93e447fa' not found.
javax.ejb.NoSuchEntityException: Instance of bean 'SecurityRatingHistoryPost' with primary key 'com.cdc.fms.server.setup
.security.ratinghistory.SecurityRatingHistoryEntityPK@93e447fa' not found.
at com.cdc.fms.server.setup.security.ratinghistory.SecurityRatingHistoryEntityBean_7x4361__WebLogic_CMP_RDBMS.__
WL_store(SecurityRatingHistoryEntityBean_7x4361__WebLogic_CMP_RDBMS.java:2208)
at com.cdc.fms.server.setup.security.ratinghistory.SecurityRatingHistoryEntityBean_7x4361__WebLogic_CMP_RDBMS.ej
bStore(SecurityRatingHistoryEntityBean_7x4361__WebLogic_CMP_RDBMS.java:2012)
at weblogic.ejb20.manager.DBManager.storeBean(DBManager.java(Compiled Code))
at weblogic.ejb20.manager.DBManager.beforeCompletion(DBManager.java(Compiled Code))
at weblogic.ejb20.internal.TxManager$TxListener.beforeCompletion(TxManager.java(Compiled Code))
at weblogic.transaction.internal.ServerSCInfo.callBeforeCompletions(ServerSCInfo.java(Compiled Code))
--------------- nested within: ------------------
weblogic.transaction.RollbackException: Unexpected exception in beforeCompletion: sync=weblogic.ejb20.internal.TxManager
$TxListener@44a824cd
Instance of bean 'SecurityRatingHistoryPost' with primary key 'com.cdc.fms.server.setup.security.ratinghistory.SecurityR
atingHistoryEntityPK@93e447fa' not found. - with nested exception:
[javax.ejb.NoSuchEntityException: Instance of bean 'SecurityRatingHistoryPost' with primary key 'com.cdc.fms.server.setu
p.security.ratinghistory.SecurityRatingHistoryEntityPK@93e447fa' not found.]
at weblogic.transaction.internal.TransactionImpl.throwRollbackException(TransactionImpl.java(Compiled Code))
at weblogic.transaction.internal.ServerTransactionImpl.internalCommit(ServerTransactionImpl.java(Compiled Code))
at weblogic.transaction.internal.ServerTransactionImpl.commit(ServerTransactionImpl.java(Compiled Code))
at weblogic.ejb20.internal.BaseEJBLocalObject.postInvoke(BaseEJBLocalObject.java(Compiled Code))
at com.cdc.fms.server.common.ConsolidatorSessionBean_fz4673_ELOImpl.processRequest(ConsolidatorSessionBean_fz467
3_ELOImpl.java:57)
at com.cdc.fms.server.common.GatewaySessionBean.processRequest(Unknown Source)
at com.cdc.fms.server.common.GatewaySessionBean_oehtlw_EOImpl.processRequest(GatewaySessionBean_oehtlw_EOImpl.ja
va:407)
at com.cdc.fms.server.common.GatewaySessionBean_oehtlw_EOImpl_WLSkel.invoke(Unknown Source)
<Jan 29, 2008 6:03:10 PM PKT> <Info> <EJB> <010051> <EJB Exception during invocation from home: com.cdc.fms.server.commo
n.GatewaySessionBean_oehtlw_HomeImpl@3e13a4aa threw exception: javax.ejb.EJBException: nested exception is: weblogic.tra
nsaction.RollbackException: Unexpected exception in beforeCompletion: sync=weblogic.ejb20.internal.TxManager$TxListener@
44a824cd
Instance of bean 'SecurityRatingHistoryPost' with primary key 'com.cdc.fms.server.setup.security.ratinghistory.SecurityR
atingHistoryEntityPK@93e447fa' not found. - with nested exception:
[javax.ejb.NoSuchEntityException: Instance of bean 'SecurityRatingHistoryPost' with primary key 'com.cdc.fms.server.setu
p.security.ratinghistory.SecurityRatingHistoryEntityPK@93e447fa' not found.]
javax.ejb.EJBException: nested exception is: weblogic.transaction.RollbackException: Unexpected exception in beforeCompl
etion: sync=weblogic.ejb20.internal.TxManager$TxListener@44a824cd
##################################################################

weblogic 7? when the current production version is 10.2?
don't play yourself. fund a project to upgrade your weblogic version.
can't tell based on what you've posted, and I fear that the stuff you'll have to post to get an answer here will be too much. this isn't a good place to come for an answer.
%

How to master good design with EJB and JSP?

I use JSP to calling EJB. But the .jsp file is complex and it's difficult to maintain...I just want to work higher efficent with EJB,JSP and JavaBean. I want to know is there a good design with EJB and JSP? and is there any good material about MVC for EJB,JSP and JavaBean?

You should read the J2EE blueprint available on this website. Better download the PDF, and print it for yourself so you can read it anytime.

Oracle or MS SQL Server, EJB Models and Web Dynpro Application

Hi
I've a table in MS SQL database. I've created in Visual Admin, the datasource(jdbc/MyAlias) for the above. SQL Server has Employee Table with EmpId, FirstName, LastName and Description as its Columns.
I want to display, modify , insert and delete entries from the Employee Table using web Dynpro. For this we have used JDBC method by which we create class file which will have JDBC connectivity and logic for getting data from backend. This class file then used for display, update and other operations. And the context is built at design time.
This is not proper method, as this doesn't come under perview of MVC concept.
I want to use EJB Models for this case. But I'm stuck with some problems.
1. How do I implement EJB models in this scenario.
2. How do EJB module (entity bean) connects to external database.
3. What are the most logical steps to be used in this case.
Any pointers for this will greatly appreciated with points?
So far I was able to do create EJB module of Entity Bean type with all interfaces. But beyond this I'm not able to proceed. Do let me know the step wise procedure for this kind of scenario.
Thanks
Srikant

Hi Srikant,
I have worked on similar stuff, but the scenario was a little different. I worked on creating Web Services using EJBs, but the basic part was that, the web service was supposed to interact with the SQL Server database. So maybe I can help you...
First thing which is needed is that you have created the JDBC Connector in your Visual Administrator correctly. If you wish to cross check, you can see my answer in the following thread:
JDBC error
In this thread itself I have given the code which is the solution to your problem (this is what i believe). I am pasting the code again:
<b>InitialContext initialContext = new InitialContext();
DataSource dataSource = (DataSource)initialContext.lookup("jdbc/MyAlias");
java.sql.Connection connection = dataSource.getConnection();</b>
You can use this code in the method of your EJB, and then you can easily use this connection object to access your database tables using SQL queries.
And if by any chance you are looking for a step wise procedure for creating a web service from an EJB, then give me your email address, i will send you the doc.
Bye
Ankur
Do reward points if it helps!!

MVC + EJB?

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