Following are my code
#RestController
public class EmployeeController {
#Autowired
EmployeeService empService;
public EmployeeController (EmployeeService Impl empServiceImpl) {
super();
this.empService = empServiceImpl;
}
}
#Service
public interface EmployeeService {
public List<EmployeeDTO> getAllEmployeeDetails()
}
public class EmployeeServiceImpl {
public List<EmployeeDTO> getAllEmployeeDetails(){
//methods business logic and repo call goes here
}
}
When I start my server I am getting below error.
Parameter 1 of constructor in
com.app.in.controller.EmployeeController required a bean of type
'com.app.in.service.EmployeeServiceImpl' that could not be found
My understanding might be wrong. If I annotate the EmployeeSeriveImpl class also with #Service then it working.Is that is the correct way to do it ? My question is the service interface is annotated with #Service still why its implementation is also required to annotation. Please let me know if I miss something in that ? What is the standard method to solve this issue ?
You can get your dependency injected using a constructor. And #Autowired is optional in this case.
This is your example, but with a few corrections:
#RestController
public class EmployeeController {
// private final is a good practice. no need in #Autowire
private final EmployeeService empService;
// this constructor will be used to inject your dependency
// #Autowired is optional in this case, but you can put it here
public EmployeeController (EmployeeService empServiceImpl) {
this.empService = empServiceImpl;
}
}
I assume you have an interface EmployeeService and class EmployeeServiceImpl which implements that interface and is Spring Bean.
Something like this:
#Service
public class EmployeeServiceImpl implements EmployeeService {}
Why this #Service is needed? When you put this annotation on your class, Spring knows this is a bean that Spring should manage for you (container will create an instance of it and inject it wherever it is needed).
Check Spring docs to get more details about Dependency Injection.
The Spring team generally advocates constructor injection, as it lets you implement application components as immutable objects and ensures that required dependencies are not null.
what is the purpose of #Autowired annotation on a constructor? What is the difference between non-annotated and annotated constructor? Thank you.
Autowiring feature enables you to inject the object dependency implicitly.
Without autowiring you have to initiate the object like:
public class SomeOperation() {
private CarService carService;
public SomeOperation() {
carService = new CarServiceImpl();
}
}
But if you annotate with #Autowired you don't have to initiate the object. The framework will bring the class which implements the carService and initiate your object with it.
public class SomeOperation() {
private CarService carService;
#Autowired
public SomeOperation(CarService carService) {
this.carService = carService;
}
}
What is the difference between non-annotated and annotated
constructor?
In Spring 3 or below, the annotation on the constructor is mandatory to make Spring consider the constructor as the way to instantiate the bean and inject dependencies provided in parameters.
Spring 4 and above versions don't require the annotation to do that.
You just need to declare the constructor with any parameter to achieve that.
So in recent Spring versions, don't clutter the code with the annotation :
public Foo(Bar bar){
this.bar = bar;
}
I'm working on a project that uses SpringBoot 2.0.5 version, Spring Data JPA to persists and retrieve records using JPA. I autowired SimpleJpaRepository in the service layer. But while starting my application, it failed with
"NoSuchBeanDefinitionException"- No qualifying bean of type
'org.springframework.data.jpa.repository.support.SimpleJpaRepository<?, ?>'
available: expected at least 1 bean which qualifies as autowire candidate.
My controller, service and DAO are like below
Controller class:
#Controller
public class MyController{
#Autowired
private MyService<Person,PersonPK> service;
Service layer as
public interface MyService<V,K>{
methods defined
}
#Service("service")
public class MyServiceImpl<V,K> implements MyService<V,K>{
#Autowired
private SimpleJpaRepository<V,K> repository; // This dependency is failing
}
Application as :
#SpringBootApplication (exclude = {SecurityAutoConfiguration.class})
#EnableJpaRepositories
public class MyApplication {
public static void main(String[] args) {
SpringApplication.run(MyApplication.class, args);
}
}
Is my approach incorrect? Is that not the correct way of autowiring the SimpleJpaRepository.
There is no need for me to extend SimpleJpaRepository as Spring provided JPARepository is good for me, for now.
Thanks
You still need to create a repository interface that extends JpaRepisitory, or the spring repository type of your choice.
To quote the spring data documentation:
1.2.1 Defining repository interfaces
As a first step you define a domain class-specific repository interface. The interface must extend
Repository and be typed to the domain class and an ID type. If you
want to expose CRUD methods for that domain type, extend
CrudRepository instead of Repository.
Once you do create a new repository type, you will autowire by that type rather than the SimpleJpaRepository.
One way to get an implementation of the SimpleJpaRepository is by using a Configuration class to create an instance as a bean that you will use inside your service.
#Configuration
public class PersistanceConfiguration {
#PersistenceContext
private EntityManager entityManager;
#Bean
public SimpleJpaRepository<YourEntity, Long> getYourEntitySimpleRepository() {
return new SimpleJpaRepository<>(YourEntity.class, entityManager);
}
}
And inject it to your service as you would do with a JpaRepository, for example:
#Service
public class YourEntityServiceImpl<YourEntity, Long> implements YourEntityService {
private JpaRepository<YourEntity, K> repository;
private SimpleJpaRepository<YourEntity, K> simpleRepository;
#Autowired
public YourEntityServiceImpl(YourEntityRepository repository, SimpleJpaRepository<YourEntity, Long> simpleRepository) {
this.repository = repository;
this.simpleRepository = simpleRepository;
}
}
You should create a repository interface that extending JpaRepisitory.
#Repository
public interface MyRepository extends JpaRepisitory<T, ID> {
//
}
And the you should Autowired in your service class.
#Service("service")
public class MyServiceImpl<V,K> implements MyService<V,K>{
#Autowired
private MyRepository myRepository;
}
Trying to inject bean in a class which has field with #Any annotation. But getting error as -
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'javax.enterprise.inject.Instance' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {#javax.inject.Inject(), #javax.enterprise.inject.Any()}
#Named
#Singleton
public class ProcessorFactoryImpl implements ProcessorFactory {
#Inject #Any
private Instance<Processor> processorList;
}
Interface is
public interface Processor {
some method
}
And implementing class is :
#Named
#Singleton
#Default
public class ProcessorImpl implements Processor {
}
For now, I have only one implementation so did not create qualifiers.
You are mixing Spring DI and CDI which are not made to work together.
Choose one of them but not both.
If you choose CDI
#Named
#ApplicationScoped
public class ProcessorFactoryImpl implements ProcessorFactory
{
#Inject
private Processor processor;
}
and
#Dependent
#Default
public class ProcessorImpl implements Processor {
// etc ...
}
In this case, the processor attribute is not a List ! You should think about what you expect. If you want a List<Processor>, you will have to use a CDI Producer instead.
If you choose Spring DI
#Component
public class ProcessorFactoryImpl implements ProcessorFactory
{
#Inject // or #Autowired
private Processor processor;
}
and
#Scope("prototype")
public class ProcessorImpl implements Processor
{
// etc ...
}
Mixing Spring and CDI
As written in the comments below, Spring can use #Inject and #Named as theses annotations are part of JSR-330.
The trouble is that too much framework mixing and using #Inject on an Instance<T>field cannot be achieved like that with Spring as it is a CDI feature.
To use the same feature, use #Provider from Spring.
Example :
CDI
#Inject
private Instance<MyClass> lazyInstance;
usage :
MyClasse instance = lazyInstance.get();
Spring
#Inject // or #Autowired
private Provider<MyClass> lazyInstance;
usage (same as CDI):
MyClasse instance = lazyInstance.get();
Have you tried List instead of Instance?
#Autowired
private List<Processor> processorList;
I'm developing an application using Spring. I need to use the #Service annotation. I have ServiceI and ServiceImpl such that ServiceImpl implements ServiceI. I'm confused here as to where should I keep the #Service annotation.
Should I annotate the interface or the implementation with #Service? What are the differences between these two approaches?
I never put #Component (or #Service, ...) at an interface, because this make the interface useless. Let me explain why.
claim 1: If you have an interface then you want to use that interface for the injection point type.
claim 2: The purpose of an interface is that it define a contract that can been implemented by several implementations. On the other side you have your injection point (#Autowired). Having just one interface and only one class that implement it, is (IMHO) useless, and violates YAGNI.
fact: When you put:
#Component (or #Service, ...) at an interface,
have multiple classes that implements it,
at least two classes become Spring Beans, and
have an injection point that use the interface for type based injection,
then you will get and NoUniqueBeanDefinitionException
(or you have a very special configurations setup, with Environment, Profiles or Qualifiers ...)
Conclusion: If you use #Component (or #Service, ...) at an interface then you must violate at least one of the two clains. Therefore I think it is not useful (except some rare scenarios) to put #Component at interface level.
Spring-Data-JPA Repository interfaces are something complete different
Basically annotations like #Service, #Repository, #Component, etc. they all serve the same purpose:
auto-detection when using annotation-based configuration and classpath
scanning.
From my experience I am always using #Service annotation on the interfaces or abstract classes and annotations like #Component and #Repository for their implementation. #Component annotation I am using on those classes which serves basic purposes, simple Spring beans, nothing more. #Repository annotation I am using in the DAO layer, for e.g. if I have to communicate to the database, have some transactions, etc.
So I would suggest to annotate your interface with the #Service and other layers depending on the functionality.
I used #Component, #Service, #Controller and #Repository annotations only on the implementation classes and not on the interface. But #Autowired annotation with Interfaces still worked for me. If there's only one implementation of your interface Spring component scan automatically finds it with just #Autowired annotation. In case you have multiple implementations, you will need to use the #Qualifier annotation along with #Autowired to inject the correct implementation at the injection point.
1. #Service on Interfaces
#Service
public interface AuthenticationService {
boolean authenticate(String username, String password);
}
Normally, that's fine, but there's a drawback. By putting Spring's #Service on interfaces, we create an extra dependency and couple our interfaces with an outside library.
Next, to test the autodetection of our new service beans, let's create an implementation of our AuthenticationService:
public class InMemoryAuthenticationService implements AuthenticationService {
#Override
public boolean authenticate(String username, String password) {
//...
}
}
We should pay attention that our new implementation, InMemoryAuthenticationService, doesn't have the #Service annotation on it. We left #Service only on the interface, AuthenticationService.
So, let's run our Spring context with the help of a basic Spring Boot setup:
#SpringBootApplication
public class AuthApplication {
#Autowired
private AuthenticationService authService;
public static void main(String[] args) {
SpringApplication.run(AuthApplication.class, args);
}
}
When we run our app, we may get the infamous NoSuchBeanDefinitionException, and the Spring context fails to start.
Therefore, placing #Service on interfaces isn't enough for the auto-detection of Spring components.
2. #Service on Abstract Classes
Using the #Service annotation on abstract classes isn't common.
We'll start by defining an abstract class from scratch and putting the #Service annotation on it:
#Service
public abstract class AbstractAuthenticationService {
public boolean authenticate(String username, String password) {
return false;
}
}
Next, we extend AbstractAuthenticationService to create a concrete implementation without annotating it:
public class LdapAuthenticationService extends AbstractAuthenticationService {
#Override
public boolean authenticate(String username, String password) {
//...
}
}
Accordingly, we also update our AuthApplication, to inject the new service class:
#SpringBootApplication
public class AuthApplication {
#Autowired
private AbstractAuthenticationService authService;
public static void main(String[] args) {
SpringApplication.run(AuthApplication.class, args);
}
}
After we run our AuthApplication, the Spring context doesn't start. It ends up with the same NoSuchBeanDefinitionException exception again.
So, using #Service annotation on abstract classes doesn't have any effect in Spring.
3. #Service on Concrete Classes
Contrary to what we've seen above, it's quite a common practice to annotate the implementation classes instead of abstract classes or interfaces.
In this way, our goal is mostly to tell Spring this class is going to be a #Component and mark it with a special stereotype, which is #Service in our case.
Therefore, Spring will autodetect those classes from the classpath and automatically define them as managed beans.
So, let's put #Service on our concrete service classes this time around. We'll have one class that implements our interface and a second that extends the abstract class that we defined previously:
#Service
public class InMemoryAuthenticationService implements AuthenticationService {
#Override
public boolean authenticate(String username, String password) {
//...
}
}
#Service
public class LdapAuthenticationService extends AbstractAuthenticationService {
#Override
public boolean authenticate(String username, String password) {
//...
}
}
We should take notice here that our AbstractAuthenticationService doesn't implement the AuthenticationService here. Hence, we can test them independently.
Finally, we add both of our service classes into the AuthApplication and give it a try:
#SpringBootApplication
public class AuthApplication {
#Autowired
private AuthenticationService inMemoryAuthService;
#Autowired
private AbstractAuthenticationService ldapAuthService;
public static void main(String[] args) {
SpringApplication.run(AuthApplication.class, args);
}
}
Our final test gives us a successful result, and the Spring context boots up with no exceptions. Both of the services are automatically registered as beans.
You might have a look at this page for the other explanations.
Pros of putting annotation on #Service is that it gives a hint that it is a service. I don't know if any implementing class will by default inherit this annoation.
Con side is that you are coupling your interface with a specific framework i.e. Spring, by using spring specific annotation.
As interfaces are supposed to be decoupled from implementation, I would not suggest using any framework specific Annotations or object part of your interface.
I would put #Service on your class but put the name of the interface as a parameter to the annotation e.g.
interface ServiceOne {}
#Service("ServiceOne")
class ServiceOneImpl implements ServiceOne{}
By doing that you get all the benefits and can still inject the interface but get the class
#Autowired
private ServiceOne serviceOne;
So your interface is not tied to spring framework and you can change the class at any time and not have to update all your injection points.
So if I wanted to change the implementation class I could just annotate the new class and remove from the first but that's all that is required to be changed. If you inject the class you could have a lot of work when ever you want to change the impl class.
One benefit of spring is to easily switch Service (or other) implementation.
For this, you need to annotate on the interface and declare variable like this :
#Autowired
private MyInterface myVariable;
and not :
#Autowired
private MyClassImplementationWhichImplementsMyInterface myVariable;
Like the first case, you can activate which implementation to inject from the moment it is unique (only one class implements the interface).
In the second case, you need to refactor all your code (the new class implementation has another name).
As a consequence, the annotation needs to be on the interface as much as possible. Furthermore, JDK proxies are well suited for this : they are created and instantiated at application startup because runtime type is known by advance, contrary to CGlib proxies.
interface MyService {}
#Service
class MyServiceImpl implements MyService{}
#Autowired
private MyService myService;
My testing result on spring-boot 2.7.4 is:
Adding #Service ONLY to interface doesn't create spring bean named MyService. It will error on Autowired.
#Service will need to be added to implementation class to create bean com.*.service.impl.MyServiceImpl $$EnhancerBySpringCGLIB$$9140ae19 Spring will wire it to private MyService myService;
There are 5 annotations which could be used for making spring beans. List in below of answers.
Do you really need an interface? If you are going to have one implementation for each service interface, just avoid it, use only class. Of course, if you don't have RMI or when interface proxy is required.
#Repository - use for injecting your dao layer classes.
#Service - use for injecting your service layer classes. In service layer also you might need to use #Transactional annotation for db transaction management.
#Controller - use for your frontend layer controllers, such as JSF managed beans injecting as spring beans.
#RestController - use for spring rest controllers, this would help you to avoid every time to put #ResponseBody and #RequestBody annotations in your rest methods.
#Component - use it in any other case when you need to Inject spring bean which is not controller, service, or dao class
To put it simply:
#Service is a Stereotype annotation for the service layer.
#Repository is a Stereotype annotation for the persistence layer.
#Component is a generic stereotype annotation used to tell Spring to create an instance of the object in the Application Context. It's possible to
define any name for the instance, the default is the class name as camel case.