In normal Spring, when we want to autowire an interface, we define it's implementation in Spring context file.
What about Spring boot?
how can we achieve this?
currently we only autowire classes that are not interfaces.
Another part of this question is about using a class in a Junit class inside a Spring boot project.
If we want to use a CalendarUtil for example, if we autowire CalendarUtil, it will throw a null pointer exception. What can we do in this case? I just initialized using "new" for now...
Use #Qualifier annotation is used to differentiate beans of the same interface
Take look at Spring Boot documentation
Also, to inject all beans of the same interface, just autowire List of interface
(The same way in Spring / Spring Boot / SpringBootTest)
Example below:
#SpringBootApplication
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
public interface MyService {
void doWork();
}
#Service
#Qualifier("firstService")
public static class FirstServiceImpl implements MyService {
#Override
public void doWork() {
System.out.println("firstService work");
}
}
#Service
#Qualifier("secondService")
public static class SecondServiceImpl implements MyService {
#Override
public void doWork() {
System.out.println("secondService work");
}
}
#Component
public static class FirstManager {
private final MyService myService;
#Autowired // inject FirstServiceImpl
public FirstManager(#Qualifier("firstService") MyService myService) {
this.myService = myService;
}
#PostConstruct
public void startWork() {
System.out.println("firstManager start work");
myService.doWork();
}
}
#Component
public static class SecondManager {
private final List<MyService> myServices;
#Autowired // inject MyService all implementations
public SecondManager(List<MyService> myServices) {
this.myServices = myServices;
}
#PostConstruct
public void startWork() {
System.out.println("secondManager start work");
myServices.forEach(MyService::doWork);
}
}
}
For the second part of your question, take look at this useful answers first / second
You can also make it work by giving it the name of the implementation.
Eg:
#Autowired
MyService firstService;
#Autowired
MyService secondService;
Assume that you have a GreetingService
public interface GreetingService {
void doGreetings();
}
And you have 2 implementations HelloService
#Service
#Slf4j
public class HelloService implements GreetingService{
#Override
public void doGreetings() {
log.info("Hello world!");
}
}
and HiService
#Slf4j
#Service
public class HiService implements GreetingService{
#Override
public void doGreetings() {
log.info("Hi world!");
}
}
Then you have another interface, which is BusinessService to call some business
public interface BusinessService {
void doGreetings();
}
There are some ways to do that
#1. Use #Autowired
#Component
public class BusinessServiceImpl implements BusinessService{
#Autowired
private GreetingService hiService; // Spring automatically maps the name for you, if you don't want to change it.
#Autowired
private GreetingService helloService;
#Override
public void doGreetings() {
hiService.doGreetings();
helloService.doGreetings();
}
}
In case you need to change your implementation bean name, refer to other answers, by setting the name to your bean, for example #Service("myCustomName") and applying #Qualifier("myCustomName")
#2. You can also use constructor injection
#Component
public class BusinessServiceImpl implements BusinessService {
private final GreetingService hiService;
private final GreetingService helloService;
public BusinessServiceImpl(GreetingService hiService, GreetingService helloService) {
this.hiService = hiService;
this.helloService = helloService;
}
#Override
public void doGreetings() {
hiService.doGreetings();
helloService.doGreetings();
}
}
This can be
public BusinessServiceImpl(#Qualifier("hiService") GreetingService hiService, #Qualifier("helloService") GreetingService helloService)
But I am using Spring Boot 2.6.5 and
public BusinessServiceImpl(GreetingService hiService, GreetingService helloService)
is working fine, since Spring automatically get the names for us.
#3. You can also use Map for this
#Component
#RequiredArgsConstructor
public class BusinessServiceImpl implements BusinessService {
private final Map<String, GreetingService> servicesMap; // Spring automatically get the bean name as key
#Override
public void doGreetings() {
servicesMap.get("hiService").doGreetings();
servicesMap.get("helloService").doGreetings();
}
}
List also works fine if you run all the services. But there is a case that you want to get some specific implementation, you need to define a name for it or something like that. My reference is here
For this one, I use #RequiredArgsConstructor from Lombok.
As mentioned in the comments, by using the #Qualifier annotation, you can distinguish different implementations as described in the docs.
For testing, you can use also do the same. For example:
#RunWith(SpringRunner.class)
#SpringBootTest
public class MyClassTests {
#Autowired
private MyClass testClass;
#MockBean
#Qualifier("default")
private MyImplementation defaultImpl;
#Test
public void givenMultipleImpl_whenAutowiring_thenReturnDefaultImpl() {
// your test here....
}
}
There are 2 approaches when we have autowiring of an interface with multiple implementations:
Spring #Primary annotation
In short it tells to our Spring application whenever we try to autowire our interface to use that specific implementation which is marked with the #Primary annotation. It is like a default autowiring setting. It can be used only once per cluster of implementations of an interface. → #Primary Docs
Spring #Qualifier annotation
This Spring annotation is giving us more control to select the exact implementation wherever we define a reference to our interface choosing among its options. → #Qualifier Docs
For more details follow the links to their documentation.
public interface SomeInterfaces {
void send(String message);
String getType();
}
kafka-service
#Component
public class SomeInterfacesKafkaImpl implements SomeInterfaces {
private final String type = "kafka";
#Override
public void send(String message) {
System.out.println(message + "through Kafka");
}
#Override
public String getType() {
return this.type;
}
}
redis-service
#Component
public class SomeInterfacesRedisImpl implements SomeInterfaces {
private final String type = "redis";
#Override
public void send(String message) {
System.out.println(message + "through Redis");
}
#Override
public String getType() {
return this.type;
}
}
master
#Component
public class SomeInterfacesMaster {
private final Set<SomeInterfaces> someInterfaces;
public SomeInterfacesMaster(Set<SomeInterfaces> someInterfaces) {
this.someInterfaces = someInterfaces;
}
public void sendMaster(String type){
Optional<SomeInterfaces> service =
someInterfaces
.stream()
.filter(service ->
service.getType().equals(type)
)
.findFirst();
SomeInterfaces someService =
service
.orElseThrow(() -> new RuntimeException("There is not such way for sending messages."));
someService .send(" Hello. It is a letter to ....");
}
}
test
#SpringBootTest
public class MultiImplementation {
}
#TestInstance(TestInstance.Lifecycle.PER_CLASS)
class SomeInterfacesMasterTest extends MultiImplementation {
#Autowired
private SomeInterfacesMaster someInterfacesMaster;
#Test
void sendMaster() {
someInterfacesMaster.sendMaster("kafka");
}
}
Thus, according to the Open/Closed principle, we only need to add an implementation without breaking existing code.
#Component
public class SomeInterfacesRabbitImpl implements SomeInterfaces {
private final String type = "rabbit";
#Override
public void send(String message) {
System.out.println(message + "through Rabbit");
}
#Override
public String getType() {
return this.type;
}
}
test-v2
#TestInstance(TestInstance.Lifecycle.PER_CLASS)
class SomeInterfacesMasterTestV2 extends MultiImplementation {
#Autowired
private SomeInterfacesMaster someInterfacesMaster;
#Test
void sendMasterV2() {
someInterfacesMaster.sendMaster("rabbit");
}
}
If we have multiple implementations of the same interface, Spring needs to know which one it should be autowired into a class. Here is a simple example of validator for mobile number and email address of Employee:-
Employee Class:
public class Employee {
private String mobileNumber;
private String emailAddress;
...
/** Getters & Setters omitted **/
}
Interface EmployeeValidator:
public interface EmployeeValidator {
public Employee validate(Employee employee);
}
First implementation class for Mobile Number Validator:
#Component(value="EmployeeMobileValidator")
public class EmployeeMobileValidator implements EmployeeValidator {
#Override
public Employee validate(Employee employee) {
//Mobile number Validation logic goes here.
}
}
Second implementation class for Email address Validator:
#Component(value="EmployeeEmailValidator")
public class EmployeeEmailValidator implements EmployeeValidator {
#Override
public Employee validate(Employee employee) {
//Email address validation logic goes here.
}
}
We can now autowired these above validators individually into a class.
Employee Service Interface:
public interface EmployeeService {
public void handleEmployee(Employee employee);
}
Employee Service Implementation Class
#Service
public class EmployeeServiceImpl implements EmployeeService {
/** Autowire validators individually **/
#Autowired
#Qualifier("EmployeeMobileValidator") // Autowired using qualifier for mobile validator
private EmployeeValidator mobileValidator;
#Autowired
#Qualifier("EmployeeEmailValidator") // Autowired using qualifier for email valodator
private EmployeeValidator emailValidator;
#Override
public void handleEmployee(Employee employee) {
/**You can use just one instance if you need**/
employee = mobileValidator.validate(employee);
}
}
I have a very simple code comprising of Service -> RequestProcessor -> DAO having 2-3 classes (interface, abstract, concrete) in each layer.
Service layer:-
public interface Service {
public void saveOrUpdate(Object entity, String operationName);
}
}
public abstract class AbstractService implements Service{
public abstract ReqProcessor getRP();
#Override
public void saveOrUpdate(Object entity, String operationName) {
ReqProcessor hiberTestRP = getRP();
hiberTestRP.saveOrUpdate(entity, operationName);
}
}
#Component
public class ServiceImpl extends AbstractService {
#Autowired
public ReqProcessor hibertestRPImpl;
#Override
public HiberTestRP getRP() {
return hibertestRPImpl;
}
}
ReqProcessor layer:-
public interface ReqProcessor {
public void saveOrUpdate(Object entity, String operationName);
public void saveObject();
}
}
public abstract class AbstractReqProcessor implements ReqProcessor {
#Override
public void saveOrUpdate(Object entity, String operationName) {
saveObject();
}
}
#Component
public class ReqProcessorImpl extends AbstractReqProcessor {
#Autowired
public CustomHibernateDao customWSDaoImpl;
#Override
#Transactional(value="transactionManagerWS", propagation=Propagation.REQUIRED)
public void saveObject() {
// object created //
customWSDaoImpl.saveOrUpdate(object); // exception is thrown at this line
}
}
DAO layer:-
public interface CustomHibernateDao {
public void saveOrUpdate(Object entity, String operationName);
}
#Repository
#Transactional(value="transactionManagerWS", propagation=Propagation.MANDATORY)
public class CustomWSDaoImpl implements CustomHibernateDao {
#Autowired
public SessionFactory sessionFactoryWS;
protected Session getCurrentSession() {
return sessionFactoryWS.getCurrentSession();
}
#Override
public void saveOrUpdate(Object entity, String operationName) {
Session session = getCurrentSession();
session.saveOrUpdate(entity);
}
}
I get the following exception at the commented line :
Exception in thread "main" org.springframework.transaction.IllegalTransactionStateException: No existing transaction found for transaction marked with propagation 'mandatory'
at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:359)
at org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:447)
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:277)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:213)
at com.sun.proxy.$Proxy37.saveOrUpdate(Unknown Source)
The code works absolutely fine when the abstract classes are removed, with only interfaces and their implementing classes remaining. But with the above setup, the transaction is not being propagated from ReqProcessor layer to the DAO layer. Please help. (Dont mind the 'public' accessors everywhere, it's just for testing)
I have also searched on SO and other forums but couldnt find a solution.
As #m-deinum has mentioned, Spring uses proxies to add "transactional" functionality, and this feature does not work when you call method annotated with #Transactional from another method of the class.
You have two ways to fix the problem:
In AbstractReqProcessor autowire ApplicationContext and then use it to get a bean of CustomHibernateDao type. On this retrieved object you can call saveObject - then the transactional magic happens.
The more preferred way is to annotate method saveOrUpdate of class AbstractService with #Transactional annotation too - then it will work again.
But I think you know the cause of the problem now and you can find another - more suitable for you - way.
When i call a service layer from controller,data are being saved in database.
My controller is:
#RestController
#RequestMapping("/api")
public class ApiController {
#Autowired(required = true)
PersonService personService; //This is service layer class
#RequestMapping("/add")
public void add(){
person.setLastName("Rahim");
person.setFirstName("Uddin");
person.setAddress("Dhaka");
person.setCity("Dhaka");
personService.add(person);
}
}
Service layer is:
#Service
#Transactional
public class PersonServiceImpl implements PersonService {
#Autowired
PersonDao personDao;
#Override
public void addPerson(Person person) {
personDao.addPerson(person);
}
}
Till now everything is ok.
But when i call the service layer through another class, null pointer exception is being shown.
At that time:
My controller is:
#RestController
#RequestMapping("/api")
public class ApiController {
#Autowired(required = true)
PersonService personService; //This is service layer class
#RequestMapping("/add")
public void add(){
MiddleClass m=new MiddleClass();
m.create();
}
}
My MiddleClass is:
public class MiddleClass {
#Autowired
PersonService personService;
public void create(){
Person person=new Person();
person.setLastName("Rahim");
person.setFirstName("Uddin");
person.setAddress("Dhaka");
person.setCity("Dhaka");
personService.addPerson(person);//this time same service layer
//is showing null pointer exception here
}
}
WHY?????????? is it for lacking of any annotation in MiddleClass?
You're creating the MiddleClass instance yourself, using new. So Spring has no way to know that it has to inject the service into the MiddleClass instance. It can only inject beans into other beans it creates itself.
So, MiddleClass must be a Spring bean, and it must be autowired into the controller, just like the service is.
I receive the following exception during program execution:
org.hibernate.ObjectDeletedException: deleted instance passed to merge: [ns.entity.Category#<null>]; nested exception is java.lang.IllegalArgumentException: org.hibernate.ObjectDeletedException: deleted instance passed to merge: [ns.entity.Category#<null>]
The following code throws exception:
importer.foo();
Importer service:
#Service
#Transactional
public class Importer {
#Autowired
private UserService userService;
#Autowired
private CategoryService categoryService;
#Transactional
public void foo() {
User user = userService.findByLogin("max");
categoryService.delete(user.getCategories());
}
}
UserService (uses CrudRepository):
#Service
#Repository
#Transactional
public class UserServiceImpl implements UserService {
#Autowired
private UserRepository repository;
#Override
#Transactional(readOnly = true)
public User findById(Long userId) {
return repository.findOne(userId);
}
}
CategoryService (uses CrudRepository):
#Service
#Repository
#Transactional
public class CategoryServiceImpl implements CategoryService {
#Autowired
private CategoryRepository repository;
#Override
#Transactional
public void delete(Set<Category> categories) {
repository.delete(categories);
}
}
The following code snippet in CategoryServiceImpl.delete() works without exception:
for (Category category : categories) {
Category newCat = findById(category.getCategoryId());
if (newCat != null) {
delete(newCat);
}
}
From what I understand two different transactions are used (one read only and one for deletion). Is it possible to re-use the transaction for all calls? Removing (readOnly = true) from UserServiceImpl.findById() does not help.
I thought that just one transaction should be used for all three methods (Importer.foo(), UserServiceImpl.findById(), CategoryServiceImpl.delete()) according to Spring documentation.
I was wondering if this recipe does not use Open Session in View or Dozer works (the scenario is a spring, jsf, hibernate application):
I have this in back-end module:
public abstract class AbstractMap<E extends Serializable> implements Mapper<E> {
public abstract E map(E e) ;
public List<E> map(List<E> l) {
List<E> map = new ArrayList<E>();
for (E t : l) {
map.add(this.map(t));
}
return map;
}
}
#Component
public class PersonService extends AbstractService<Person>{
#Autowired
PersonDAO personDao;
#Transacted
public List<Person> findPeople(Mapper<Person> m, PersonFilter filter) {
return m.map(personDao.findByFilter(filter));
}
}
In front-end I have this jsb bean:
#Component
#Scope("session")
public class PersonBean {
#Autowired
PersonService personService;
PersonFilter personFilter;
List<Person> getPeople() {
return personService.findPeople(new AbstractMap<People>() {
public Person map(Person person) {
Person dto = new Person();
dto.setName(person.getName());
dto.setAddresses(new AbstractMap<Address>() {
public Address map(Address a) {
Address dto = new Address();
dto.setStreet(a.getStreet());
return dto;
}
}.map(person.getAddresses()));
return dto;
}
}, personFilter);
}
}
From my point of view has some advantages:
front-end must to indicate that it want to retrieve every invocation to back-end.
if need use a mapper in more than a place, I can move map code to a external class.
back-end open and close transaction.
don't need duplicate code to define DTOs for Person and Address.
What problems that could cause this proposed solution?