I have a entity class called Customer, I am using this entity object in another class to set the data. When I use this object below like
#Autowired
Customer customer
Spring is complaining that please configure the bean in your classes.
Can we use auto wiring with entity objects?
You can only autowire only those beans whose life-cycle are managed by Spring IoC container.
These beans are defined in xml form with </bean> tag, or with some special annotations like #Bean, #Component, #Service, #Repository etc.
On the other hand,
in simple terms, entities are some java objects that you will need to create, update by yourself according to your business logic and save/update/remove them in/from DB. Their life-cycle cannot be managed by Spring IoC container.
So, you should never feel like you need to autowire an entity if you are doing it right!
In fact, Spring support #Autowire only for Spring Beans. A java class becomes Spring Bean only when it is created by Spring, otherwise it is not.
A workaround might be to annotate your class with #Configurable but you would have to use AspectJ
Please look in the Spring documentations on how to use #Configurable
Also, I wonder why you would autowire an entity class ?
I would warn you not to mix Spring Bean and JPA entities in one class/usecase because:
Spring Beans are instantiated and managed by Spring
Entities are managed by JPA provider
If you mean JPAs #Entity-annotation, Spring is simply telling you, that there isn't a bean in its context.
On startup/runtime classes in the application will be scanned and each class annotated with spring annotations like #Component, #Service etc. will be instantiated as beans and put into a global context (Spring applicationcontext).
This context is then used to lookup and inject those beans into other beans when #Autowired is found during scanning.
Opposed to this, #Entity is used during the creation of the Persistence-Context of JPA (as far as I remember) which isn't aware of Spring and it's context.
Most of the solutions to make both contexts aware of each other a mostly a little bit hacky.
Related
I have a Spring 3 project which acts as a Rest API, and wanted to wire a spring bean I have into an unmanaged class for logging purposes.
After trying many different things, what worked was marking my unmanaged class with the annotation #Configurable.
Like:
#Configurable
public class ClassNotManagedBySpring {
#Autowired
#Qualifier("myBean")
private MyBean myBean;
}
#Service("myBean")
public class MyBean {
#Autowired
#Qualifier("someOtherBean")
private SomeOtherBean someOtherBean;
}
And then in my beans.xml:
<context:spring-configured/>
So now let's say that ClassNotManagedBySpring.java, is one of 6 classes that all do something similar, except 3 of them ARE managed by spring because they have the #Component annotation.
But all 6 of these classes need to #Autowire MyBean.java and only some need the #Configurable annotation.
To note, I was already previously using AspectJ in this app for multiple other purposes.
I want to know what is the risk in my spring application by all of a sudden wiring spring managed dependencies into un managed classes in this way?
Can there be performance issues? Risks of errors at runtime?
If this isn't the best way of wiring a spring managed bean into an unmanaged class, what is?
I've been using #Configurable for years without issues, it's a very easy solution if you need app instantiated beans configured by Spring. My use cases were all in the UI tier. I also used #Configurable(preConstruction = true) whenever I needed autowired values already in the constructor. Of course, if you make millions of #Configurable objects it might be a performance issue, otherwise I wouldn't worry too much about it. The only small aesthetic problem I had was Eclipse giving me some red underlines at class definitions extending #Configurable classes, complaining that the hierarchy of class SomeClass is inconsistent, but it compiled them nevertheless, no errors in the Problems view or at runtime whatsoever.
I have this interface:
public interface liteRepository extends CrudRepository<liteEntity, Long>, JpaSpecificationExecutor<liteEntity> {...}
It works, all is well.
However, intellij does not register this class as a spring component. If I annotate this interface with #Component, then intellij recognizes this as a spring bean and I can #Autowire this repository in my integration tests.
My code still works after annotation, but I'm not confident that I am not messing with things that I should not be messing with.
Question:
Is there any harm in adding the #Component annotation to this interface?
The only thing that #Component annotation means is that the class is eligible for becoming a Spring bean during Spring's component-scan.
So, if you want it to be a Spring bean and you did not define it as a Spring bean anywhere else, you can safely add the #Component annotation.
Of course, this will only work if you have the actual component scan configured somewhere(for, example <context:component-scan base-package="..."> in some Spring config file), which I am assuming you already heave, since the bean is properly getting autowired after you add the annotation.
I am new to Spring framework.While reading dependency injection i found out two ways to inject beans anotationbased and xml based.
In xmlBased it is quite simple that you define one bean inside your application context xml file.
eg.
<bean id="wild" class="com.javapapers.spring.ioc.Wolf" />
<bean id="zoo" class="com.javapapers.spring.ioc.Zoo">
<property name="wild" ref="wild" />
</bean>
but in Annotation based configuration we just have to write
<context:component-scan base-package="com.javapapers.spring.ioc" />
I want to know how it will load "wild" and "zoo" .
Does it means it will load all beans or only specific which is written under #Service annotation..???
I also want to know how it is loaded ..??? is all beans gets initialized when application is loaded..??
Thanks ...!!
When you use <context:component-scan base-package="com.javapapers.spring.ioc" />, spring will instanciate all classes that are in the "com.javapapers.spring.ioc" package and have one of this annotation :
#Service
#Controller
#Repository
...
And yes, all beans gets initialized when you launch your application.
You can have more info in this page : here
Beans get initialized through an ApplicationContext, which is also a BeanFactory. With an XML configuration, you would need an implementation of that interface, ClassPathXmlApplicationContext. Your application needs to create such a class, register your XML file(s), and refresh the context. When that is done, Spring will start creating your beans by reading the configuration.
When it hits the <component-scan> element, Spring will scan your declared packages for any classes annotated with #Component or its specializations. From the docs:
In Spring 2.0 and later, the #Repository annotation is a marker for
any class that fulfills the role or stereotype (also known as Data
Access Object or DAO) of a repository. Among the uses of this marker
is the automatic translation of exceptions.
Spring 2.5 introduces further stereotype annotations: #Component,
#Service, and #Controller. #Component is a generic stereotype for any
Spring-managed component. #Repository, #Service, and #Controller are
specializations of #Component for more specific use cases, for
example, in the persistence, service, and presentation layers,
respectively.
Therefore, you can annotate your component classes with #Component,
but by annotating them with #Repository, #Service, or #Controller
instead, your classes are more properly suited for processing by tools
or associating with aspects. For example, these stereotype annotations
make ideal targets for pointcuts.
Thus, if you are choosing between using #Component or #Service for
your service layer, #Service is clearly the better choice. Similarly,
as stated above, #Repository is already supported as a marker for
automatic exception translation in your persistence layer.
When it finds those classes, it will create an instance of each of them.
As for how it does this, it's a little more complicated. The overall strategy is with reflection. However, because of your configuration, Spring will sometimes generate (java or cglib) proxies instead of clear instances so that it can add behavior.
All the steps are described in detail in the official documentation.
Will be loaded all beans annotated with
#Controller
#Component
#Service
#Repository
which are inside a packages com.javapapers.spring.ioc, and its subpackages.
I am trying to understand the javax.inject package and I am not clear what the javax.inject.Named annotation is supposed to be used for. The Javadoc does not explain the the idea behind it.
Javadoc is at http://download.oracle.com/javaee/6/api/javax/inject/Named.html
I am using Spring 3.0 to write some sample programs, by putting #Named on a bean it seems to add it to the bean factory but the Javadoc description is so light I can't tell if that is the standard behavior or Spring specific behavior.
My questions are:
What is the difference between #Named and #Qualifier
How are you supposed to tell the Runtime system a class should be injectable in other classes what's the annotation for that? The equivalent of #Component in Spring?
Update 1 there is an excellent explanation of #Named and #Qualifier at Nice article about #Named and #Qualifier https://dzone.com/articles/java-ee6-cdi-named-components thanks #xmedeko for linking to it the comment below.
Use #Named to differentiate between different objects of the same type bound in the same scope.
#Named("maxWaitTime")
public long maxWaitTimeMs;
#Named("minWaitTime")
public long minWaitTimeMs;
Without the #Named qualifier, the injector would not know which long to bind to which variable.
If you want to create annotations that act like #Named, use the #Qualifier annotation when creating them.
If you look at #Named, it is itself annotated with #Qualifier.
#Inject instead of Spring’s #Autowired to inject a bean.
#Named instead of Spring’s #Component to declare a bean.
Those JSR-330 standard annotations are scanned and retrieved the same way as Spring annotation (as long as the following jar is in your classpath)
Regarding #2, according to the JSR-330 spec:
This package provides dependency
injection annotations that enable
portable classes, but it leaves
external dependency configuration up
to the injector implementation.
So it's up to the provider to determine which objects are available for injection. In the case of Spring it is all Spring beans. And any class annotated with JSR-330 annotations are automatically added as Spring beans when using an AnnotationConfigApplicationContext.
The primary role of the #Named annotation is to define a bean for the purpose of resolving EL statements within the application, usually through JSF EL resolvers. Injection can be performed using names but this was not how injection in CDI was meant to work since CDI gives us a much richer way to express injection points and the beans to be injected into them.
If I create an EJB3 bean (say a stateless session bean) in an application using Spring 2.5 for DI, how should I inject dependencies from Spring into the bean without coupling the bean to Spring?
I don't know if you consider applying an interceptor as coupling but that's to my knowledge the standard approach. From the Chapter 18. Enterprise Java Beans (EJB) integration of the documentation:
18.3.2. EJB 3 injection interceptor
For EJB 3 Session Beans and
Message-Driven Beans, Spring provides
a convenient interceptor that resolves
Spring 2.5's #Autowired annotation
in the EJB component class:
org.springframework.ejb.interceptor.SpringBeanAutowiringInterceptor.
This interceptor can be applied
through an
#Interceptors
annotation in the EJB component class,
or through an interceptor-binding XML
element in the EJB deployment
descriptor.
#Stateless
#Interceptors(SpringBeanAutowiringInterceptor.class)
public class MyFacadeEJB implements MyFacadeLocal {
// automatically injected with a matching Spring bean
#Autowired
private MyComponent myComp;
// for business method, delegate to POJO service impl.
public String myFacadeMethod(...) {
return myComp.myMethod(...);
}
...
}
SpringBeanAutowiringInterceptor by
default obtains target beans from a
ContextSingletonBeanFactoryLocator,
with the context defined in a bean
definition file named
beanRefContext.xml. By default, a
single context definition is expected,
which is obtained by type rather than
by name. However, if you need to
choose between multiple context
definitions, a specific locator key is
required. The locator key (i.e. the
name of the context definition in
beanRefContext.xml) can be
explicitly specified either through
overriding the
getBeanFactoryLocatorKey method in a
custom
SpringBeanAutowiringInterceptor
subclass.
The only other option I'm aware of (extending the EJB 2.x support classes) is much worse from a coupling point of view (and thus doesn't answer your question).
See also
Default Injecting Spring bean to EJB3 SLSB without #Autowired Annotation