I have a custom annotation that is declared as a Spring managed Service:
#Service
public #interface MyServiceAnnotation {
// my service url
String url();
}
The above declaration enables my services to be autowired as Spring Managed beans.
#MyServiceAnnotation(url="/path/serviceLocation")
public class SomeService {
doWork();
}
However, there are certain services that have their bean definitions in an applicationContext.xml. Adding the #MyServiceAnnotation to such beans makes them both Autowiring enabled, as well as inject dependecy through the xml file.
Due to issues related to legacy code, I don't want to remove the xml bean definitions and make them all autowired.
So, is there a way in which I could turn off autowiring in this case, and still use #MyServiceAnnotation? Ideally I would like to have the #Service annotation on MyServiceAnnotation, the existing services would still use the #MyServiceAnnotation but would get their dependencies injected based on the xml. All the new services would be autowired without the xml bean definitions.
One possible approach is to create NonSpringManagedMyServiceAnnotation that is same as MyServiceAnnotation, but without the #Service annotation on it. The downside of this is that I'd have to duplicate rest of the code from MyServiceAnnotation, which I don't want to.
This is one approach, may not be that optimal though. I am assuming you would have specified a component-scan tag in your xml to scan the classes having the Spring stereotype annotations, these tags support a exclude-filter sub-tag to ignore specific patterns. If the files that you specify follow a specific pattern(specific packages, specific names etc) then you may simply be able to specify this sub-tag to ignore classes holding your annotation.
<context:component-scan base-package="mypackage">
<context:exclude-filter type="regex" expression=".*ToBeIgnoredNaming"/>
</context:component-scan>
I think you should try to maintain separation of concern.
Adding #Service on your annotation makes it a de facto Spring service : since this is not the behavior you want, you may simply have a simple #MyAnnotation (with url property) on each services (legacy and new).
Then you add Spring's #Service annotation on each new service to enable bean registration by annotation.
Related
I have a collection of classes which I want to be injected into the Spring application context. However, these classes can only be guaranteed to be annotated with one of a group of annotations I have written - i.e. I can assume it will be annotated with #MyAnnotation, but not #Component.
However, #MyAnnotation forms part of an API for my project, and I don't want to state an explicit dependency of this API on Spring. Thus, I can't annotate #MyAnnotation with #Component in order to have it be transitively picked up by Spring.
Is there a way to tell Spring to additionally include #MyAnnotation in its classpath scanning without adding this dependency to my API?
Currently I'm manipulating the bean definition registry to 'manually' add each class annotated with #MyAnnotation, but I'd prefer to rely on Spring's inbuilt support.
Thanks in advance.
It's possible if you create your own BeanDefinitionRegistryPostProcessor to register your own beans. If you implement the postProcessBeanDefinitionRegistry method, you can add beans to the registry by yourself, for example:
#Component
public class FooFactoryBean implements BeanDefinitionRegistryPostProcessor {
#Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
registry.registerBeanDefinition(..);
}
}
To obtain these bean definitions, you can use the ClassPathScanningCandidateComponentProvider class, which will create BeanDefinition objects for all classes found for a specific filter. In this case, an AnnotationTypeFilter will work:
ClassPathScanningCandidateComponentProvider scanner = new ClassPathScanningCandidateComponentProvider(false);
scanner.addIncludeFilter(new AnnotationTypeFilter(Foo.class));
Set<BeanDefinition> definitions = scanner.findCandidateComponents("com.example.my");
In this example, it will find all classes annotated with #Foo in the com.example.my package.
#Configuration classes and XML based configuration should work for you. Have a look at this tutorial: https://www.tutorialspoint.com/spring/spring_java_based_configuration.htm
But to get your #MyAnnotations picked up is more difficult (see #g00glen00b's answer), and I'm not sure it makes sense if the above mentioned solutions are available.
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.
Using Spring, one can define classes that implement MessageSourceAware. The container will then inject a MessageSource automatically (see the tail end of this documentation).
Is this a special case or can I use this concept to inject other dependencies too? For instance, can my classes implement the following interface:
public interface MyServiceAware {
void setMyService(MyService service);
}
and then somehow be auto-wired with a suitable bean?
Note: I am using XML configuration exclusively at the moment and I'd be reluctant to move to Java-based annotations.
The *Aware interfaces are handled by a BeanPostProcessor that is automatically registered in the application context (org.springframework.context.support.ApplicationContextAwareProcessor).
You could create and register your own postprocessor to handle MyServiceAware beans.
Remember also that the XML configuration does support autowiring for appropriately configured beans.
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.
I created a custom sterotype #Action, and Spring has managed to detect it in the package scan I configured in the configurations.
The next step I would like to do is to tell Spring that all classes with #Action should be created with prototype, instead of Singleton.
My #Action interface is as follows:
#Target({ElementType.TYPE})
#Retention(RetentionPolicy.RUNTIME)
#Documented
#Component
public #interface Action {
}
I tried to mark it with #Scope("prototype") but that does not seem to help.
Is what I desire possible?
Kent
The context:component-scan can be configured with a custom scope-resolver, which implements org.springframework.context.annotation.ScopeMetadataResolver.
I created a custom scope-resolver that not only checks the bean for a #Scope annotation (with the default resolver of org.springframework.context.annotation.AnnotationScopeMetadataResolver), but looks up annotations of annotations too (recursively).
One thing to note though, that looking up annotations recursively might go into an endless loop, as java.lang.annotation.Documented is annotated with java.lang.annotation.Documented. Best to maintain a table that indicates which annotation has been looked up already.
Unfortunately not with spring 2.5.X. Your #Component-annotation describes the role of the bean while the scope is a separate axis, so a role and scope descriptor typically have to be applied separately to the implementation class. When viewed in this way it makes some sense (edit: at least it did so for a few seconds, anyway)
I don't know how this will change i spring 3.x, which is not too far away. There seems to be some room for improvement.