I've been developing my first Java EE app, which has a number of JPA entity classes, each of which have a corresponding EJB class for dealing with the business logic. What I've done is changed one of those beans from Stateless to SessionScoped, so I can use it to allow a user to work their way through a series of form fields, all of which are rendered on a JSF form.
However, I'm starting to think this is clearly wrong, as I'm doing things like implementing methods such as "submitStep1" and "goBackToStep2" in my EJB. These methods set indicators which are used by render elements of various tags on the JSF page, so they are clearly "presentation logic".
My question is, how should I re-structure my code? I'm thinking that I should just have one SessionScoped (or should that be stateful?) bean, which deals with the presentation logic of my JSF page, and is able to use all the other ejbs (and by extension my JPA classes). This bean would be in the presentation-tier level of my app, meaning my business logic tier wouldn't need any Session Scoped Session Beans.
Now this all makes sense to me, and is what I am probably going to do. However the reason for my question is that on my JSF xhtml pages I use JSF EL tags a lot to refer to EJB content. Are there any JPA-related pitfalls I need to watch out for when writing presentation tier classes?
I know my question is pretty vague, and not really related to a specific example. And although I've found quite a lot out about Stateful v Stateless beans on this and other sites I just want to know my intended structure is the best one.
Why don't you use backing beans for presentation purpose, as they are intended for it, and you can easyly configure its scope, and leave the EJBs to business tier?
When using entities directly on the presentation tier, you should be aware of the transaction scope, specially regarding lazy relationships. That is, normally it is used one transaction per request, what will mean that amongst different requests, the entities will become detached, so you will need to reatach them to be able to load lazy relationships. You could use a filter that does it automatically each request or handle it by hand. You could also keep the same transaction during different requests but a long transaction is normally not a good idea, specially if there are updates/creations in the DB during this transacion.
Related
I am not sure whether my approach with the MVC environment in JSF is the best way to go. Since I am trying to get the most out of JSF I would like to know how my Service Layer (or Model, speaking in MVC terms) should be 'designed'.
I know the View-Controller ratio should be 1 to 1 (exceptions ruled out).
Now in what way should I design my Service Layer? Should I use one big service (don't think so)? If not, based on what should I split my services?
Note, my Service will be called from the Beans (Controllers in MVC terms) and the Service itself will call DAO's using JPA when necessary.
Thanks in advance
The service layer (the business model) should be designed around the main entity (the data model). E.g. UserService for User, ProductService for Product, OrderService for Order, etc. You should absolutely not have one huge service class or so. That's extreme tight coupling.
As to the service layer API itself, Java EE 6 offers EJB 3.1 as service layer API. In the dark J2EE ages, long time ago when EJB 2.0 was terrible to develop with, Spring was more often been used as service layer API. Some still use it nowadays, but since Java EE 6 has incorporated all the nice lessons learnt from Spring, it has become superfluous. Note that EJB (and JPA) is not available in barebones servletcontainers such as Tomcat. You'd need to install for example OpenEJB on top of it (or just upgrade to TomEE).
Regardless of the service layer API choice, best would be to keep your JSF backing bean (action)listener methods as slick as possible by performing the business job entirely in the service layer. Note that the service layer should by itself not have any JSF dependencies. So any (in)direct imports of javax.faces.* in the service layer code indicates bad design. You should keep the particular code lines in the backing bean (it's usually code which adds a faces message depending on the service call result). This way the service layer is reuseable for other front ends, such as JAX-RS or even plain servlets.
You should understand that the main advantage of the service layer in a Java EE application is the availability of container managed transactions. One service method call on a #Stateless EJB counts effectively as a single DB transaction. So if an exception occurs during one of any DAO operations using #PersistenceContext EntityManager which is invoked by the service method call, then a complete rollback will be triggered. This way you end up with a clean DB state instead of a dirty DB state because for example the first DB manipulation query succeeded, but the second not.
See also:
Creating master-detail pages for entities, how to link them and which bean scope to choose
When is it necessary or convenient to use Spring or EJB3 or all of them together?
JSF Controller, Service and DAO
The 1:1 ratio between services and model entities maybe not bad if you have few entities in your app. But if it is a big app, there would be too much services.
The number of services depends upon the use cases of the app you are designing. Once you have identified them in the analysis phase, you must group them in several groups according to their functionality. Each group of use cases will be a Service, and each use case will be a method in that service. Each Service can manage several model entities (and you have to inject in it the DAOs it needs to perform its functionality). Usually the uses cases of a Service manage model entities inter-realationated in the class diagram of the model. The Services might follow the good practice of "max cohesion / min coupling".
The ratio between DAOs and model entities is 1:1. Each DAO perform CRUD operations and queries of its entity. If a method needs to query 2 relationated entities, put it in the more suitable DAO depending on the business concepts.
In the JSF presentation layer I neither have a 1:1 ratio between pages and controllers, that would be too much controllers. I group into one contrller all the pages needed to perform the use cases of each service. So the ratio 1:1 is between controllers and services, injecting each service in the controller whose pages perform its use cases.
Of course, these are general principles. You may have some particular cases in the app that broke them, but they are few.
You might not have too much services and controllers, but not too few neither because then they would have too much logic and fields. You must acchieve a compromise.
I'm a little confused by the mixed use of JSF2+Spring+EJB3 or any combination of those. I know one of the Spring principal characteristics is dependency injection, but with JSF managed beans I can use #ManagedBean and #ManagedProperty anotations and I get dependency injection functionality. With EJB3 I'm even more confused about when to use it along with JSF or if there is even a reason to use it.
So, in what kind of situation would it be a good idea to use Spring+JSF2 or EJB3+JSF2?
Until now I have created just some small web applications using only JSF2 and never needed to use Spring or EJB3. However, I'm seeing in a lot of places that people are working with all this stuff together.
First of all, Spring and EJB(+JTA) are competing technologies and usually not to be used together in the same application. Choose the one or the other. Spring or EJB(+JTA). I won't tell you which to choose, I will only tell you a bit of history and the facts so that you can easier make the decision.
Main problem they're trying to solve is providing a business service layer API with automatic transaction management. Imagine that you need to fire multiple SQL queries to perform a single business task (e.g. placing an order), and one of them failed, then you would of course like that everything is rolled back, so that the DB is kept in the same state as it was before, as if completely nothing happened. If you didn't make use of transactions, then the DB would be left in an invalid state because the first bunch of the queries actually succeeded.
If you're familiar with basic JDBC, then you should know that this can be achieved by turning off autocommit on the connection, then firing those queries in sequence, then performing commit() in the very same try in whose catch (SQLException) a rollback() is performed. This is however quite tedious to implement everytime.
With Spring and EJB(+JTA), a single (stateless) business service method call counts by default transparently as a single full transaction. This way you don't need to worry about transaction management at all. You do not need to manually create EntityManagerFactory, nor explicitly call em.getTransaction().begin() and such as you would do when you're tight-coupling business service logic into a JSF backing bean class and/or are using RESOURCE_LOCAL instead of JTA in JPA. You could for example have just the following EJB class utilizing JPA:
#Stateless
public class OrderService {
#PersistenceContext
private EntityManager em;
#EJB
private ProductService productService;
public void placeOrder(Order newOrder) {
for (Product orderedproduct : newOrder.getProducts()) {
productService.updateQuantity(orderedproduct);
}
em.persist(newOrder);
}
}
If you have a #EJB private OrderService orderService; in your JSF backing bean and invoke the orderService.placeOrder(newOrder); in the action method, then a single full transaction will be performed. If for example one of the updateQuantity() calls or the persist() call failed with an exception, then it will rollback any so far executed updateQuantity() calls, and leave the DB in a clean and crisp state. Of course, you could catch that exception in your JSF backing bean and display a faces message or so.
Noted should be that "Spring" is a quite large framework which not only competes EJB, but also CDI and JPA. Previously, during the dark J2EE ages, when EJB 2.x was extremely terrible to implement (the above EJB 3.x OrderService example would in EJB 2.x require at least 5 times more code and some XML code). Spring offered a much better alternative which required less Java code (but still many XML code). J2EE/EJB2 learned the lessons from Spring and came with Java EE 5 which offers new EJB3 API which is even more slick than Spring and required no XML at all.
Spring also offers IoC/DI (inversion of control; dependency injection) out the box. This was during the J2EE era configured by XML which can go quite overboard. Nowadays Spring also uses annotations, but still some XML is required. Since Java EE 6, after having learned the lessons from Spring, CDI is offered out the box to provide the same DI functionality, but then without any need for XML. With Spring DI #Component/#Autowired and CDI #Named/#Inject you can achieve the same as JSF does with #ManagedBean/#ManagedProperty, but Spring DI and CDI offers many more advantages around it: you can for example write interceptors to pre-process or post-process managed bean creation/destroy or a managed bean method call, you can create custom scopes, producers and consumers, you can inject an instance of narrower scope in an instance of broader scope, etc.
Spring also offers MVC which essentially competes JSF. It makes no sense to mix JSF with Spring MVC. Further Spring also offers Data which is essentially an extra abstraction layer over JPA, further minimizing DAO boilerplate (but which essentially doesn't represent the business service layer as whole).
See also:
What exactly is Java EE?
JSF Controller, Service and DAO
#Stateless beans versus #Stateful beans
There's no real easy answer here as Spring is many things.
On a really high level, Spring competes with Java EE, meaning you would use either one of them as a full stack framework.
On a finer grained level, the Spring IoC container and Spring Beans compete with the combination of CDI & EJB in Java EE.
As for the web layer, Spring MVC competes with JSF. Some Spring xyzTemplate competes with the JPA interfaces (both can use eg Hibernate as the implementation of those).
It's possible to mix and match; eg use CDI & EJB beans with Spring MVC, OR use Spring Beans with JSF.
You will normally not use 2 directly competing techs together. Spring beans + CDI + EJB in the same app, or Spring MVC + JSF is silly.
This question probably does not fit SO rules, but I'll ask it anyway. Answers might help other people struggling with JSF.
We are using JSF (MyFaces, PrettyFaces, PrimeFaces and Spring) on one of our biggest project for two years now (migrated from Tapestry 3). I can say that we are "recovering" from this migration to this day.
In my opinion one of our major mistakes was misunderstanding of JSF's VIEW SCOPE. JSF offers two basic mechanisms how you can persist VIEW STATE - CLIENT and SERVER. We went for the SERVER method, which was our first mistake as ViewExpiredException never stopped coming from that moment on. The next mistake was to store data on VIEW SCOPE as that prevented us from easily switching to CLIENT state saving method.
So I was thinking whether there are some best practices and guidelines on what should and shouldn't be stored on VIEW SCOPE (and thus serialized into VIEW STATE). Official documentation and specification does not provide that. But I came to a quite nice conclusion:
You should only store on VIEW SCOPE such information that you would normally (without JSF) pass as request parameters.
When you have a basic CRUD application without JSF, you would do this:
state of the form is preserved between requests by form values in POST parameters
state of the list (filtering, sorting, paging) is preserved between requests by query parameters
Is my conclusion correct? Do you have any other guidelines on what to store and what to never store inside VIEW SCOPE? Do any component frameworks have such guidelines?
i use the following Guidelines:
avoid VIEW SCOPE as it is only available for Faces Manages Beans.
better: avoid the usage of Faces Managed Backing Beans. use CDI Managed Backing Beans to ensure portability. (sure, this is only possible if you have any cdi container available... in Java EE 6 and newer...)
avoid AJAX with JSF. (or only use it with caution for simple UIs...)
I am using ZK Framework right now in one of my application. ZK Framework supports MVC as well as MVVM design pattern. Now for a new project I would like to use JSF. Does JSF support the both the design patterns or only MVC?
No, MVVM design pattern not supported by jsf only MVC support.It is used only desktop application.JSF also know as MVC fremework.
From http://blog.oio.de/2011/12/05/jsf-and-mvvm/:
The first M in MVVM stands for Model, and it is the very same model that we use in our MVC approach. In fact MVVM does not replace MVC, I rather prefer to see it as an additon to MVC, so there is nothing new here.
The first V in MVVM stands for View and again, there is nothing new to this part. It is the component that takes care of the client side representation. So there wont be any notable change to our views since we will continue to define them using Facelets.
VM in MVVM stands for the ViewModel, our client side model. The ViewModel is bound to the Model but it is exisitent only on the client side, though you are free to sync it whenever needed with the Model on the server side. But, more important is, that you can do whatever you want on the client side without having to send callbacks to the server.
First of all we need a next-generation-JSF-implementation, which supports the MVVM concept. The ViewModel would be created by this yet to come JSF implementation before a requested view is delivered to the client. Our ViewModel will be created from one or more JSF Managed Beans that form the Model. I can think of a nice set of class- and field-level annotations to tell JSF what parts of our model should make up the ViewModel on the client side. Once the view is delivered to the client, the ViewModel will be manipulated by client side scripts upon the form is submitted. Then, in the following iteration of the request processing lifecycle, JSF has to deal with resynchronization between ViewModel and Model. Admittedly, this might be the most tricky part, but I’m confident that the Next-Gen JSF Impl will manage to do that ;-)
From Understanding JSF as a MVC framework:
The nodes M, V and C are a maximum connected graph, meaning each part can communicate with every other part. E.g. if the model changes, it can push this change to the view. This is particularly visible in case there are multiple representations of the view in a desktop application. Change one, and see the other update in real-time.
Due to the client/server and request/response nature of web applications, classic MVC doesn't map 1:1 to most web frameworks.
More information find this link: http://www.tutorialspoint.com/jsf/jsf_architecture.htm
I disagree with user2860053's answer because it makes unnecessary assumptions about MVVM. MVVM is not about client and server responsibilities. The blog post cited only argues that a specific web application scenario involving a combination of client-side MVVM (as implementend by knockout.js) with server-side MVVM doesn't work well with JSF. It doesn't say anything about server-side MVVM.
In my understanding (which IMO corresponds to the original definition that is also referred to by the ZK documentation), the core ideas of MVVM are:
a) to keep a distinction between the UI's concrete structure, controls and layout (i.e. the view) and its state and behaviour (i.e. the viewmodel), and
b) link these using a two-way data binding.
Figuratively speaking, starting from "MVC", part a) adds the "VM", and part b) removes the "C" so we yield "MVVM":
In MVC, the controller is written for a specific view class/interface, and it's the controller's responsibility to read user input from the view, convert it and write it to the model, and to invoke business logic according to the user's action.
In contrast, MVVM doesn't have any controllers that are tightly coupled with view or model. Instead, there is a generic mechanism which uses declarative two-way data bindings for filling the view with data and converting user input and feeding it to the model, and for binding controls to business code (or presentation-only actions from the viewmodel).
So how does this apply to JSF?
In JSF, you don't write a controller for every Facelets page you write, but let the JSF lifecycle do the work of filling model elements with data from submitted forms and invoking methods according to the user's actions according to EL bindings, so the second property b) always holds for JSF.
As for the first property a), it's up to the programmer to implement high-level view state and behaviour in separate classes.
JSF puts more focus on creating components for view state and behaviour.
Viewmodels are made specifically for one kind of view, and model the whole abstract state and behaviour of the view, so I think that even "light-weight" composite components are too generic to take the role of a viewmodel. But there is nothing to prevent the developer from creating his own classes for this, i.e. write one's own viewmodel classes and bind them in the EL context.
In conclusion, JSF is not made specifically for MVVM, but contains mechanisms that can be used for implementing (server-side) MVVM.
I have looked at several JavaEE 6 login tutorials using servlet 3.0 and JSFtechnology. Often it shows a request scoped credentials bean and a user manager session bean. Most do not provide packaging info or for simplicity sake create everything in one package. I have been struggling with the packaging between the web tier and the business logic. I do not know if backing bean, controller, manager, and facade are all talking about the same thing or not. A short answer could tell me how to package a user manager session bean and the credentials bean, but a more appreciated answer would help me navigate the web tier and the business logic. Thanks in advance.
For packaging I like to break first by functionality (like core, gui) and then by business unit level.
for e.g
com.comp.db.beans // place your database beans here (if using any orm )
com.comp.web.ui.controller // place your controller, managedbeans here, this can be again broken into functionality wise like login, processing e.t.c.
com.comp.web.ui.beans //you place your vo here
In order to start packaging you have to first write down the different functionality of your system.
Then break them into business unit wise
Then break those into more finer level, to distinguish if functionality is going to be very specific to ui, or does it belong to core.