Can I somehow group a set of annotations on an abstract class, and every class that extends this class has automatically assigned these annotations?
At least the following does not work:
#Service
#Scope(value = BeanDefinition.SCOPE_PROTOTYPE)
class AbstractService
class PersonService extends AbstractService {
#Autowired //will not work due to missing qualifier annotation
private PersonDao dao;
}
The answer is: no
Java annotations are not inherited unless the annotation type has the #Inherited meta-annotation on it: https://docs.oracle.com/javase/7/docs/api/java/lang/annotation/Inherited.html.
Spring's #Component annotation does not have #Inherited on it, so you will need to put the annotation on each component class. #Service, #Controller and #Repository neither.
The short answer is: with the annotations that you mentioned in your example, no.
The long answer: there is a meta-annotation called java.lang.annotation.Inherited. If an annotation itself is annotated with this annotation, then when a class is annotated with it, its subclasses are also automatically annotated with it by implication.
However, as you can see in the spring source code, the #Service and #Scope annotation are not themselves annotated with #Inherited, so the presence of #Service and #Scope on a class is not inherited by its subclasses.
Maybe this is something that can be fixed in Spring.
I have this piece of code in my project and it works just fine, although it's not annotated as Service:
public abstract class AbstractDataAccessService {
#Autowired
protected GenericDao genericDao;
}
and
#Component
public class ActorService extends AbstractDataAccessService {
// you can use genericDao here
}
So you don't need to put annotation on your abstract class but even if you do you will still have to put annotation on all subclass as #Component or #Service annotations are not inherited.
Related
Can I somehow group a set of annotations on an abstract class, and every class that extends this class has automatically assigned these annotations?
At least the following does not work:
#Service
#Scope(value = BeanDefinition.SCOPE_PROTOTYPE)
class AbstractService
class PersonService extends AbstractService {
#Autowired //will not work due to missing qualifier annotation
private PersonDao dao;
}
The answer is: no
Java annotations are not inherited unless the annotation type has the #Inherited meta-annotation on it: https://docs.oracle.com/javase/7/docs/api/java/lang/annotation/Inherited.html.
Spring's #Component annotation does not have #Inherited on it, so you will need to put the annotation on each component class. #Service, #Controller and #Repository neither.
The short answer is: with the annotations that you mentioned in your example, no.
The long answer: there is a meta-annotation called java.lang.annotation.Inherited. If an annotation itself is annotated with this annotation, then when a class is annotated with it, its subclasses are also automatically annotated with it by implication.
However, as you can see in the spring source code, the #Service and #Scope annotation are not themselves annotated with #Inherited, so the presence of #Service and #Scope on a class is not inherited by its subclasses.
Maybe this is something that can be fixed in Spring.
I have this piece of code in my project and it works just fine, although it's not annotated as Service:
public abstract class AbstractDataAccessService {
#Autowired
protected GenericDao genericDao;
}
and
#Component
public class ActorService extends AbstractDataAccessService {
// you can use genericDao here
}
So you don't need to put annotation on your abstract class but even if you do you will still have to put annotation on all subclass as #Component or #Service annotations are not inherited.
I have a classA which implements an interfaceA, with a methodA, then I have a classB in which I call classA with an #Autowired to be able to use methodA, but it gives me a warning that I must create a method for classA. Why is this happening? Doesn't #Autowired work like this in this case? Should I just instantiate classA? Thank you very much for your answers.
ClassA
#RequiredArgsConstructor
public class RepositoryImpl implements IRepository {
#Autowired
private final TransactionDataMapper transactionDataMapper;
#Autowired
private SpringDataColminvoice springDataColminvoice;
#Override
public <S extends TransactionDto> S save(S s) {
Colm colm = transactionDataMapper.toEntity(s);
//methodA
springDataColminvoice.save(colm);
return null;
}
}
InterfaceA
public interface IRepository extends IRepository<TransactionDto, Integer> {}
ClassB
#Service
#RequiredArgsConstructor
public class ServiceImpl implements IInvoiceService {
#Autowired
private RepositoryImpl repositoryImpl;
#Override
public void save(CMessage cMessage) throws HandlerException {
try {
TransactionDto transactionDto = cMessage.getTransaction();
// methodA
repositoryImpl.save(transactionDto);
} catch (Exception e) {
throw new HandlerException(e.getMessage());
}
}
}
Exception
Action:
***************************
APPLICATION FAILED TO START
***************************
Description:
Field RepositoryImpl in com.st.ms.yyu.d.binvoce.infraestructure.rest.spring.services.impl.InvoiceServiceImpl required a bean of type 'com.st.ms.yyu.d.binvoce.infraestructure.db.springdata.repository.impl.ServiceImpl' that could not be found.
The injection point has the following annotations:
- #org.springframework.beans.factory.annotation.Autowired(required=true)
Action:
Consider defining a bean of type 'com.st.ms.yyu.d.binvoce.infraestructure.db.springdata.repository.impl.RepositoryImpl' in your configuration.
(posting this as an answer since I do not have enough reputation to comment)
As others have pointed out already, a code sample would help tremendously.
That being said, though, it sounds like you're missing implementation for "ClassA".
If you have an interface that "ClassA" implements, you have to implement the interface's methods in "ClassA" before you can use them.
I assume your code currently looks somewhat like this?
public interface InterfaceA {
void methodA();
}
public class ClassA implements InterfaceA {
}
public class ClassB {
#Autowired
ClassA classA; // Cannot use {#link InterfaceA#methodA} because the class does not implement the function
}
If this is your code, make sure you add an implementation for your "methodA()" function in "ClassA". Somewhat like so:
public class ClassA implements InterfaceA {
#Override
public void methodA() {
}
}
Additionally, in order to autowire in Spring (Boot), you need to ensure that the class you'd like to autowire is marked as such. You can autowire beans.
To make "ClassA" in the example eligible for autowiring, make sure to instantiate it either as:
A bean (using the #Bean annotation).
A component (using the #Component annotation).
A service (using the #Service annotation).
Any of the other annotations that may match your use case the best.
In our example, this would look somewhat like this:
#Component // Or #Service / whatever you may need
public class ClassA implements InterfaceA {
#Override
public void methodA() {
}
}
Hope you've found any of this helpful. All the best!
-T
As what I have understood, #Autowire means injecting the value/instance of the specific property where you put the annotation #Autowire. In this case, #Autowire only happens when there is defined/created Bean within your basePackage of your Spring Boot project that can match it, i.e. where your #Autowire referred to (meaning there is no conflict issue like ambiguity, etc. and the DataType(Class) can be implicitly casted). In your example, first you treat the IRepository and/or RepositoryImpl as Repository without using the #Repository annotation to inform the Spring Boot default configuration that this is a Repository bean. As you didn't put the POM.xml or posted the related code, I presumed you are creating your own repository class. I think it's much better to post your dependencies here.
But as what others pointed out. You need to create a bean that can match the #Autowired you've put on TransactDataManager & SpringDataColminvoice. You need also to inform the Spring Boot or register it that your class A is a Bean by annotating
#Bean - defining a regular bean,
#Component - a Component in the Project,
#Service - a Service in the Project,
#Repository - a Repository (if you're using Spring JPA), etc.
#<Other Annotations depending of what other Spring Project/Dependencies your using>
Since newer versions of Spring is moving to annotation based from XML mapping, we need to put proper annotation for each class/object that we want to be auto injected/instantiated from #Autowired using the above sample annotations depending on the role/purpose of your class/object is.
I suggest if you're not sure. Then create a typical bean using common annotation #Bean. So your class A might be
#Component //Insert proper Annotation for your class if necessary. This is just a sample
#RequiredArgsConstructor
public class RepositoryImpl implements IRepository {
#Autowired
private final TransactionDataMapper transactionDataMapper;
#Autowired
private SpringDataColminvoice
springDataColminvoice;//segunda
#Override
public <S extends TransactionDto> S save(S s) {
//Some implementation
}
#Bean
private TransactionDataMapper getTransactionDataMapper(<Some parameters if needed>){
return <an instance for TransactionDataManager>;
}
#Bean
private SpringDataColminvoice getSpringDataColmInvoice(<Some parameters if needed>){
return <an instance for SpringDataColminvoice>;
}
}
Note that 2 beans definition are optional if there are already a Beans define on outside class or if it was marked by other annotation like #Service, #Component or other proper annotations and the other one bean is just a reference parameter for the other bean in order to properly instantiated.
In your class B is the following:
public class ClassB {
#Autowired
ClassA classA;
/*Note: ignore this Bean definition if Class A is annotated with #Component,
#Service, or other proper #Annotation for Class A.
*/
#Bean
private ClassA getClassA(<Some Parameters if Needed>){
return <Instance of Class A>
}
}
Take note that, you don't need to put a Bean definition inside the Class B if you put a proper annotation for your Class A like #Component, #Service, etc.
Are #Component, #Service and #Repository optional in Spring Boot 2?
Example If have a controller class called FirstController annotated with #Controller, #RestController and #RequestMapping. I also have service classes called FirstService and SecondService and a repository called FirstRespository.
I didn't annotate any of the class except FirstController but still my application works.
Does this mean that those stereotype annotations are not required for your app to make it work? You just need it for convention and if you need to modify behaviour like scope etc.
Thanks for answering in advance.
They are not required in order for your application to work BUT they will not be picked up by Spring on your application launch nor you will have benefits of that annotation specification
#Component - generic stereotype for any Spring-managed component
#Repository - stereotype for the persistence layer
#Service - stereotype for service layer
Any code can pass when you write your Spring application, but annotation helps Spring to understand what should be created as a bean or a component and for which use.
Consider this:
#Service
public class MyService {
private IComponent component;
#Autowired
public MyService(IComponent component) {
this.preparingService = preparingService;
}
}
In order to autowire a class implementing IComponent, you need to have that class decorated with #Service or #Component in order for Spring to inject it into MyService when MyService is itself of course injected in your controller.
I have a hierarchy of classes. I want mark them with #Component. I'm trying to mark only the parent class. I expect Spring will mean childs as components too. But it doesn't happen.
I tried to use custom #InheritedComponent annotation like described here. It doesn't work.
I wrote an unit test. It fails with: "No qualifying bean of type 'bean.inherit.component.Child' available". Spring version is 4.3.7.
#Target(ElementType.TYPE)
#Retention(RetentionPolicy.RUNTIME)
#Component
#Inherited
public #interface InheritedComponent {}
#InheritedComponent
class Parent { }
class Child extends Parent {
}
#Configuration
#ComponentScan(basePackages = "bean.inherit.component")
class Config {
}
#RunWith(SpringJUnit4ClassRunner.class)
#ContextConfiguration(classes = Config.class)
public class InheritComponentTest {
#Autowired
private Child child;
#Test
public void name() throws Exception {
assertNotNull(child);
}
}
You can use a ComponentScan.Filter for this.
#ComponentScan(basePackages = "bean.inherit.component",
includeFilters = #ComponentScan.Filter(InheritedComponent.class))
This will allow Spring to autowire your Child, without you having to attach an annotation to Child directly.
To answer the question posed under the accepted answers "How do do in XML"
This is taken from Spring in Action with a trivial example by me.
Annotate the base class with component, add a qualifier
#Component
#InstrumentQualifier("TUBA")
public class Instrument {}
Qualify the subclass - NOTE- No need for #component
#InstrumentQualifier("GUITAR")
public class Guitar extends Instrument {}
Inject it like so
#Autowired
#InstrumentQualifier("GUITAR")
public void setInstrument(Instrument instrument) {this.instrument =instrument;}
In context.xml, add an include filter for assignable type
<context:component-scan base-package="some.pkg">
<context:include-filter type="assignable" expression="some.pkg.Instrument"/>
</context:component-scan>
The type and expression work as define the strategy here.
You could also use the type as "annotation" and the expression would be the path to where the custom qualifier is defined to achieve the same goal.
I am learning struts+spring, I have a struts action class:
public class Testction{
private String type;
private TestService service;
//...ignore getters and setters here
public String test(){
// action method
}
}
Can Spring inject different TestService implementation according to type parameter ? TestService is just a interface.
If this is possible, where shoud I put #service annotation? on interface or implementation class ?
If that is impossible or hard to go, how to do it in code ?
Spring helps us a lot, but also can make me confused when I want to think deeper.Take above code as example, "type" seems injected by struts, and "service" is injected by spring if TestService is annotated by #service.
so complex...
You can define a #Service annotation on the TestService implementation class.
put #Service annotation on implementation class.you can use #Inject inject TestService into TestAction Class.please remember use javax.inject package.