Is it enough to convert a POJO like Util class to an EJB session bean by putting an annotation (#Stateless or #Stateful) and using injected EntityManager in it?
Yes, #Stateless in enough. Your bean will then become an EJB bean.
The only other requirement is that you can't create such a bean with new. You have to inject it using #EJB in another managed bean (JSF managed bean, Servlet, etc). Or if you aren't yet in any kind of managed bean, you can bootstrap a bean using a JNDI lookup.
Also, EJBs indeed greatly reduce the boilerplate code of starting and committing transactions when working with JPA.
Well It is enough but still few things need to be taken Care,
1) Mark your Entity manager and other new variables to Transient if POJO is used to persist some object.
2) It is better not to do so, as If u need to make it as EJB better to Create Some New Class for it as it is suggested way to not to create complexity.
Related
I need to declare a Spring bean using Annotation-based config, which will be available throughout the runtime of the Application Server (in my case, JBoss). I should be able to write and read the data to/from the bean across multiple requests. I have read about the global session scoped bean, but couldn't find any concrete examples. Is there a way to implement this and what are the thread-safety concerns with this kind of bean?
Best Regards,
Chandra.
I am using EJB in order to take advantages of:
Concurrent (instead of creating 2 threads, I divided the work into 2
EJB beans).
Pooling (I use stateless EJB a lot and I love the idea that the pool
contains a specific number of bean). This way, I am not afraid of
running out of memory. Memory usage is more predictable).
Asynchronous processing (all I need is just an annotation).
Well, the problem is I am using it with MongoDB so I don't need any transaction. I can use #TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED) and #TransactionAttribute(TransactionAttributeType.NEVER) annotations but... it means I must specify it everywhere?
Is there anyway to disable EJB transaction by default?
In an EJB 3.0 container, annotate your EJB (or EJB method) with:
#Stateless
#TransactionManagement(TransactionManagementType.BEAN)
#TransactionAttribute(value=TransactionAttributeType.NEVER)
public class YourBean
for BEAN management. For CONTAINER management instead:
#Stateless
#TransactionManagement(TransactionManagementType.CONTAINER)
#TransactionAttribute(value=TransactionAttributeType.NEVER)
public class YourBean
The default value is managed by the container but if you dont specify nothing to do i think you solve your problem.
Or annotate all the Ejb to don´t support transaction
#Stateless
#TransactionManagement(TransactionManagementType.NEVER)
public class YourBean
Remember that the ejb transactions are executed in a hierarchical way, ie if the first method being invoked does not support methods "children methods" are handled in the same way
I would like to know the difference between creating an DAO Object with constructor like :
myDaoObject = new MyDaoObject();
and creating it by EJB injection :
#EJB
MyDaoObject myDaoObject;
Is there a difference in the running and/or performance ?
thanks.
Well...you really can't create EJBs with constructor because you would lose the functionality offered by the container (dependency injection, pooling, calling of #PostConstruct, transactions, ...). So only correct way is
#EJB
MyDaoObject myDaoObject;
P.S. Or, in case you are using CDI, #Inject instead of #EJB
I have Enterprise Java Bean which is Statefull and it holds current user instance
I want to get this instance from few different baking beans (SessionScoped managed beans) but when Im using:
#EJB
UserSessionBean usb;
(...)
usb.getUser();
I am getting null pointer exceptions in the ManagedBean (seems that every managedbean is getting new instance of UserSessionBean EJB. Why is that? I thought one instance of that bean would be shared among all Beans for that session...
if UserSessionBean is the implementation class or interface?
I think you should use the interface to create an instance of your EJB.
also take a look at #statefull and #singlton annotations.
We all know that in the web tier there is the possibility that only a single instance of a given Servlet exists which services multiple requests. This can lead to threading issues in instance variables.
My question is, is it safe to inject an EJB using the #EJB annotation into a servlet as an instance variable?
My initial instinct would be no, under the assumption that the same instance of the EJB would service multiple requests at the same time. It would seem that this would also be the instinct of a number of other programmers: Don't inject to servlets
However have I jumped to the wrong conclusion. Clearly what is injected into the servlet is a proxy, under the hood does the container actually service each request with a different instance and maintain thread safety? As this forum would suggest: Do inject to servlets
There seems to be a lot of conflicting opinions. WHICH IS CORRECT???
It is safe to inject an EJB in a Servlet as a Servlet instance variable, as long as the EJB is Stateless. You MUST NEVER inject a Stateful Bean in a Servlet.
You must implement your EJB stateless in that it doesn't hold any instance variable which itself holds a stateful value (like Persistence Context). If you need to use the persistence context, then you must get an instance of it IN the methods of the EJB. You can do that by having a PersistenceContextFactory as a EJB instance Variable and then you get an instance of the entity manager from the Factory in the method of the EJB.
The PersistenceContextFactory is thread-safe, thus it can be injected in an instance variable.
As long as you comply to the above mentioned rules, it should be thread-safe to inject a Stateless Bean in a Servlet
Your reference "Don't inject to servlets" mentions nothing about ejbs or #ejb annotation. It talks about not thread safe objects such as PersistenceContext.
Per EJB spec you can access ejbs from variety of remote clients including servlets (EJB 3.0 Specification (JSR-220) - Section 3.1). Injecting ejb using #EJB annotation is a method of obtaining EJB interface via dependency injection (section 3.4.1) which is alternative to looking up ejb objects in the JNDI namespace. So there is nothing special about #EJB annotation with respect to EJBs obtained.
So, based on EJB 3.0 Spec, it's a standard practice to obtain ejbs from servlets using #EJB annotation.
It's a mixed bag.
Stateless session beans may be injected and are safe. This is because even if a single instance of a stub is used, access to the methods will be serialized by the container.
I think what inferreddesign says is not true. It doesn't matter if the stateless session bean uses a persistence context. Only one caller will ever access a single bean instance at the same time, so even though the persistence context is not thread safe, the EJB guards against multiple access to it. Think of it as if every session bean method has the synchronized keyword applied to it.
The main problem with injecting an EJB in a Servlet I think is performance. The single stub instance will become a major area of contention when multiple requests are queuing up while waiting for a session bean method to be executed for them.
I think the simple answer is that you aren't guaranteed that it is safe.
The reason for this is that there is nothing explicit in the EJB specification that says EJB home interfaces have to be thread safe. The spec outlines the behaviour of the server side part only. What you will probably find is that the client skeletons are actually thread safe but you would need to look at how they are implemented by the library you are using. The annotation part will just expand into a service locator so that doesn't buy you anything.