The Java EE specification states that an EJB injection like this:
#EJB MyInterface myBean;
will create en entry in the Enterprise Naming Context, viz. java:comp/env/<FQN>.MyInterface/myBean. It is up to the deployer to bind this context entry to a real value and to inject this value in the myBean field.
Now I have the feeling I am missing something here:
Why is the context entry necessary? An instance of the requested EJB will be injected, so why is the entry in the context needed? Why does the injection has to happen via the context entry?
All the received answers did not address the issue: why is an ENC entry needed if the injection annotation gives enough information to resolve the injection (so my first thought was that it was redundant).
The answer is that the injection can be overridden in the deployment descriptor. This is because the EJB standard defines developer roles.
It assumes that the "bean provider" can request an injection, even provide default values. But the "application assembler" can override these values. The "bean provider" is assumed to use annotations or XML, and the "assembler" is assumed to mainly use the XML.
That is why the EJB standard defines this relation between the ENC and an injection.
I think if you need to inject an Stateful Session Bean you gonna need some context that knows the relation between your EJB instance and some previously injected EJB dependency (to that instance).
It is to allow you lookups by somehow obtained string.
Related
I'm trying to setup a Weld-JUnit4 Test for a JavaEE Bean which uses a TimerService. The Application runs in a Wildfly Application Server an So the TimerService is injected into the bean via #ResourceAnnotation.
In Weld-JUnit I have to bind Resources via:
WeldInitiator.from(<Some class).bindResource(nameOfRessource, <TimerServiceMock>)
But this doesn't work. The mock will not be injected.
So I tried #Resouce(name = "myTimer")in the JEE Bean. This doesn't work too.
So I tried #Resouce(lookup = "myTimer")in the JEE Bean. This works in my Testcase. But in ProductionCode this will change the lookupbehaviour. So it is no valid solution.
How it is possible to Mock the TimerService in a WeldJunitTest? Is there any kind of default lookup for the java.ejb.TimerService?
Thank you for your help.
EJB Spec states
16.14 TimerService References
The container must make the TimerService interface available either through injection using the Resource annotation or in JNDI under the name java:comp/TimerService, in addition to through the EJBContext interface. The authenticationType and shareable elements of the Resource annotation must not be specified.
So it should work if you use that name with the lookup attribute.
Alternatively:
16.2.2 Annotations for Environment Entries
[...]
A field of the bean class may be the target of injection. The field must not be final. By default, the name of the field is combined with the name of the class in which the annotation is used and is used directly as the name in the bean’s naming context. For example, a field named myDatabase in the class MySessionBean in the package com.acme.example would correspond to the JNDI name java:comp/env/com.acme.example.MySessionBean/myDatabase. The annotation also allows the JNDI name to be specified explicitly.
So you can also bind the JNDI-name that corresponds to the name of the field. It would allow you to get away with even less overhead in the EJB itself, but at the cost of breaking the test whenever you rename the field.
My app is being deployed on to IBM WebSphere. I have a simple service and I'd like to know how dependency injection works in this case.
// stateless EJB
#Stateless
public class UserService {
private UserDAO userDAO;
// btw, UserDAO is stateless EJB as well
#Inject
public UserService(UserDAO userDAO) {
this.userDAO = userDAO;
}
// biz methods ...
}
It fails with the following error:
[ERROR ] CWWKZ0002E: An exception occurred while starting the
application my-app. The exception message was:
com.ibm.ws.container.service.state.StateChangeException:
com.ibm.ws.cdi.CDIException:
com.ibm.wsspi.injectionengine.InjectionException:
com.ibm.ejs.container.EJBConfigurationException: EJB class
com.demo.app.UserService must have a
public constructor that takes no parameters
I remember there was something in EJB spec that says: the class must have a public constructor that takes no parameters and it makes sense for me that the bean instance is first instantiated by the container and afterward dependency injection is done.
On the other hand, I've found this in WELD docs:
First, the container calls the bean constructor (the default
constructor or the one annotated #Inject), to obtain an instance of
the bean.
And I am confused a little bit, why my EJB cannot be instantiated.
How is the EJB instance being created and dependencies injected when we have constructor injection point?
Any ideas? :)
So what happens is that you do not meet the requirements for initializing EJB beans.
CDI spec has some limitations on constructors - either no-args or one with #Inject.
But there is also this chapter, which specifies that in EE, the set of rules is extended by what EJB session beans require.
And now we are getting into EJB spec which requires a no-arg constructor on a bean.
This should be in chapter Enterprise Bean Class where it states
The class must define a public constructor that takes no arguments.
Now, finally moving on to whether this should work - e.g. can you have an EJB bean using CDI constructor injection?
Well, let's have a look at CDI TCK, a set of tests that all implementation and containers have to pass in order to be able to claim they implement CDI.
There, we can see this bean and this test using it - so yea, this can work, but you need to have both constructors.
EJBs are registered as CDI beans. But first they have to meet the requirements of the EJB spec.
I guess it works just by providing the no-args constructor.
the creation of EJB session beans is done by EJB container but it can choose to use CDI to provide EE resource injection but EJB resolution is delegated to the container
https://docs.jboss.org/weld/reference/2.1.0.Final/en-US/html/ri-spi.html says:
Alternatively, the integrator may choose to use CDI to provide EE
resource injection. In this case, the EE_INJECT environment should be
used, and the integrator should implement the Section A.1.4, “EJB
services”, Section A.1.7, “Resource Services” and Section A.1.5, “JPA
services”.
....
Weld registers resource injection points with
EjbInjectionServices, JpaInjectionServices, ResourceInjectionServices
and JaxwsInjectionServices implementations upfront (at bootstrap).
This allows validation of resource injection points to be performed at
boot time rather than runtime
if you interested in how CDI and EJB are integrated. you can have a look at the code of weld-EJB module and weld-integration(glassfish code)
For various reasons I need to perform a manual lookup of SessionContext. In JBoss5, the solution
InitialContext initialContext = new InitialContext();
SessionContext sessionContext = (SessionContext) initialContext.lookup("java:comp/EJBContext");
has served med well, but from JBoss 7 I instead get a
javax.naming.NameNotFoundException: EJBContext -- service jboss.naming.context.java.global.EJBContext
Has something changed in how context is looked up in JBoss 7.2, or is my deployment lacking anything vital? For reference, standard injection works fine, this is the only lookup that fails. Or am I doing something terribly wrong (besides performing a manual lookup of SessionContext)?
According to specification of Java EJB (this one is for EJB 3.2. but nothing changed about EJBContext from previous one, EJB 3.x), you can inject EJBContext into your components either using annotation #Resource or manually via lookup (section 11.15):
The container must make a component’s EJBContext interface available either through injection
using the Resource annotation or in JNDI under the name java:comp/EJBContext
Standard way of looking up for EJB resource is via EJBContext.lookup method but there is also JNDI way which is the only possibilities if you don't have already EJBContext:
Context initCtx = new InitialContext();
EJBContext ejbCtx = (EJBContext) initCtx.lookup("java:comp/EJBContext");
This is exactly what you did, so what is wrong? There are two things, which one I'm not sure about. First, with manually lookup it's sometime needed to assign resource to component with annotation at class level:
#Resource(name = "EJBContext", type = javax.ejb.EJBContext)
public class MyComponent {
...
}
but I'm not sure is it needed for EJBContext as well, I guess not. The second thing, more important and critical - according to specification once again:
EJBContext objects accessed through the naming environment are only valid within the bean
instance that performed the lookup.
this one is section 11.15.1, and the next one, section 11.15.2:
The Container Provider is responsible for providing an appropriate EJBContext object to the refer-
encing component. The object returned must be of the appropriate specific type for the bean requesting
injection or performing the lookup—that is, the Container Provider must return an instance of the SessionContext interface to referencing session beans and an instance of the MessageDrivenCon-
text interface to message-driven beans.
Those both mean that injection and lookup for EJBContext are only valid in Enterprise Java Beans, so those which are annotated with #MessageDriven, #Stateful, #Singleton or #Stateless (or described as EJBs in deployment descriptor file, also as EJB 2.x Specification). Maybe your component isn't valid EJB and it's why lookup isn't working? This is only suggestion of course.
There's one more possibilities to get EJBContext (more correctly SessionContext). Your component should implements SessionBean interface which has setSessionContext(SessionContext sessionContext) method. This method should be invoked by EJB container every time when component is used (injected somewhere, invoked by client or timeout, especially when it's created) and inside this method you should assign sessionContext parameter to bean's field.
I'm writing a service registry class. This service registry will scan packages for annotated classes and then populate some internal map. What I need then, is to be able to query for services (by String name) using some method (let's say Object get(String name)). This method will then search internal map for a service with such name and returns instance.
What I'm doing right now, is having this ServiceRegistryBean implement ApplicationContextAware and BeanDefinitionRegistryPostProcessor and a list of Strings (package names) given on construct.
Then, as soon as the bean is constructed, registry post processor kicks in (see note) and the registry class adds the service classes as new beans (singleton, lazy loaded) to the spring bean registry. Then, getting the service instance is as simple as requesting a bean from context, returning singleton instance.
My question is: is there a better way in Spring to do this? I've looked into bean factories, but it does not seem to me the same. Support for auto-wiring and DI in service instances is essential, that's why I want Spring to instantiate it. Also, I like the idea of Spring taking care of singletons.
Note: I've found out, that when I inline the bean creation in <constructor-arg> (that is, bean is not named and is just an instance passed as constructor argument of other bean - in my case, I'm passing registry as a parameter to other constructor), BeanDefinitionRegistryPostProcessor interface methods (namely public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry)) is not called at all! I'm quite sure, it is some behavior of Spring I don't know about, but I was not able to find proper documentation for the post-processor.
Thank you for any hints or insights!
Scanning for custom annotations it's already supported, you only need to add a include-filter to <context:component-scan> tag, ie
<context:component-scan base-package="org.example">
<context:include-filter type="annotation" expression="some.Annotation"/>
</context:component-scan>
see http://static.springsource.org/spring/docs/current/spring-framework-reference/html/beans.html#beans-scanning-filters
If you turn on default-lazy-init I suppose that the DI Container is ready to use as Service Locator Registry.
About the note, only root bean definitions are taken into account when looking for BeanFactoryPostProcessors, inner beans are ignored.
Usually, scanning and registering beans is done by BeanDefinitionParsers instead because you known when the beans are registered and beans are visible for tools, like STS Spring Bean Explorer, but using a BeanDefinitionRegistryPostProcessor is correct. The interface ensures that beans are defined before other BeanFactoryPostProcessors run.
#SpringBean
PDLocalizerLogic loc;
When using above I receive java.io.NotSerializableException. This is because loc is not serializable, but this shouldn't be problem because spring beans are a serializable proxies.
I'm using wicket-spring library, and as injector SpringComponentInjector, where wrapInProxies is by default set to true, so I think that proxies should be created, but they aren't.
On the page https://cwiki.apache.org/WICKET/spring.html#Spring-AnnotationbasedApproach is written:
Using annotation-based approach, you
should not worry about
serialization/deserialization of the
injected dependencies as this is
handled automatically, the
dependencies are represented by
serializable proxies
What am I doing wrong?
Do you know how the bean is being injected?
Through component initialization (i.e. a Component and being filled in by the SpringComponentInjector)
Some other object using InjectorHolder.getInjector().inject(this)?
Injected directly by spring (i.e. this is a spring bean where the property is being set by Spring configuration)
Cases 1 and 2 would use wicket-spring integration and would wrap the bean with a wicket proxy which is serializable.
Case 3 would only provide you whatever spring passes to you without wrapping.
First, make sure your bean is really proxied. By default spring does not create proxies.
Second, check your proxying strategy - whether it is proxy-target-class="true" or not. If it is false, (afaik) a reference to your object is stored in the invocation handler of the JDK proxy, and is attempted to be serialized.
So you'll need to make your class Serializable as well, if you need it to be.
Can you double check that the instantiation listener is added in your application class:
addComponentInstantiationListener(new SpringComponentInjector(this));
Also, this only works for fields in Wicket components, not arbitrary classes.
See also wicket #SpringBean can not create bean