Trying to generate error about Spring's @Autowired field injection for JUnit

Question

I am working with Spring 4.0.7, and with JUnit about testing of course.

About DI Spring offers @Autowired to be used in three locations

constructor
setter
field

I always work through the two first, why never the third option?

Because I remember have read long time ago about field injection should not be used, because it has a negative consequence about Testing. It does JUnit fails.

Note: Only for Testing is the problem. To runtime or production all goes well

Objective: For demonstration/academic purposes I want generate this problem.

I have the following:

Repository

public interface PersonRepository extends JpaRepository<Person, String>{

}

A Service

@Service
@Transactional
@Profile("failure")
public class PersonFailTestServiceImpl implements PersonService {

    private static final Logger logger = ...

    @Autowired
    private PersonRepository personRepository;

Other Service (calling or using the service shown above)

@Service
@Transactional
@Profile("failure")
public class PersonFailTestProcessImpl implements PersonProcess {

    private static final Logger logger = ...

    @Autowired
    private PersonService personService;

How you can see the two services are based on Field Injection.

Now the testing:

How the beans are loaded

    @Configuration
    @ComponentScan( basePackages={"com.manuel.jordan.server.infrastructure"},
                    basePackageClasses={PersonProcess.class,PersonRepository.class, PersonService.class})
    public class CentralConfigurationEntryPoint {

    }

    @ContextConfiguration(classes=CentralConfigurationEntryPoint.class)
    public class CentralTestConfigurationEntryPoint {
    }

Now the two testing classes

@Transactional
@RunWith(SpringJUnit4ClassRunner.class)
@ActiveProfiles({"development","failure"})
public class PersonServiceImplDevelopmentFailureTest extends CentralTestConfigurationEntryPoint {

    @Autowired
    private PersonService personService;

    @Test
    public void savePerson01(){
        Person person01 = PersonFactory.createPerson01();
        personService.save(person01);
        personService.printPerson(personService.findOne("1"));
    }

@Transactional
@RunWith(SpringJUnit4ClassRunner.class)
@ActiveProfiles({"development","failure"})
public class PersonProcessImplDevelopmentFailureTest extends CentralTestConfigurationEntryPoint{

    @Autowired
    private PersonProcess personProcess;

Well all the testing methods pass, all green. I don't know if I am missing something or through Spring 4 the problem has been fixed

score 2 · Answer 1 · answered Oct 03 '14 at 03:11

2

If this was your premise or problem

Because I remember have read long time ago about field injection should not be used, because it has a negative consequence about Testing. It does JUnit fails.

then you thought wrong. There is nothing inherently wrong with using field injection, definitely nothing that would cause JUnit tests to fail in and of itself. If a bean exists, Spring will be able to inject it whether it's in a constructor, a setter method, or a field.

Since you've activated your failure profile, your PersonFailTestServiceImpl bean will be found.

answered Oct 03 '14 at 03:11

Sotirios Delimanolis

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I forget to say some months ago I have watched a demo (not recorded) about how JUnit fails when the `@Autowired` is defined on the field in a service or repository, and how JUnit works when the `@Autowired` is defined in a constructor. Seems the problem is not about how `resolve` bean, is about `reflection`.. about the *reading*, was on some posts. – Manuel Jordan Oct 03 '14 at 03:20
@ManuelJordan That must have been a very specific scenario. – Sotirios Delimanolis Oct 03 '14 at 03:24
Yes. A specific scenario…. the slide contains `Even when field is private – but hard to unit test.` – Manuel Jordan Oct 03 '14 at 03:25
1

@ManuelJordan If you want, please post the exact scenario so we can answer for that. Otherwise, no, in general, field injection will work just as well as constructor or setter injection. The issue here is more from a design perspective. – Sotirios Delimanolis Oct 03 '14 at 03:28
Let me consult with the other student assistant, perhaps he remembers of the case, but I remember was easy, I am wondered why I can't reproduce the same scenario. – Manuel Jordan Oct 03 '14 at 03:31
Was it using `new` for the service bean? – chrylis -cautiouslyoptimistic- Oct 03 '14 at 03:46
No, nothing about `new` – Manuel Jordan Oct 03 '14 at 03:48
Seems the problem should arise with `Mock` http://stackoverflow.com/questions/9807882/unit-testing-a-class-with-autowired-notation-using-junit-and-easymock tomorrow I am going to do some experiments. – Manuel Jordan Oct 03 '14 at 03:48
@ManuelJordan Using constructor or setter _injection_ wouldn't have helped in that case. – Sotirios Delimanolis Oct 03 '14 at 03:59
@SotiriosDelimanolis Can you please assist me with this http://stackoverflow.com/questions/26231165/improve-performance-on-sending-bulk-emails-through-spring-mail/26233308#26233308 – Santhosh Oct 07 '14 at 10:15
@SanKrish Seems like you got an answer. Is there still an issue? – Sotirios Delimanolis Oct 07 '14 at 15:29
@SotiriosDelimanolis would be greatfull if you provide an answer with your suggestion. – Santhosh Oct 08 '14 at 05:20
@SanKrish I don't have much experience in the field of sending batch emails, but the top answers seem very promising. – Sotirios Delimanolis Oct 08 '14 at 05:34

score 1 · Accepted Answer · answered Oct 03 '14 at 14:21

I think I can help. The example code you've posted here is a good example of a system / integration test, not a UNIT test.

If you were UNIT testing PersonFailTestProcessImpl, you would have to set the personRepository dependency yourself through code. But it is private, so how do you do this? You cannot use a constructor or setter since none is provided. This is what is meant by 'hard to unit test'.

Java 5+ provides a way to set private variables like this via reflection (the so-called privileged accessor). Basically, you obtain the class, get the declared field, call its setAccessible method, then you can set its value directly. There are libraries that will do these steps for you, but the point is that this is a pain compared to X.setSomething();

So there is nothing that 'makes jUnit fails' by using @Autowired on a private field. But building an object model without constructors or setters for establishing dependencies is unnecessarily constraining.

Thank You, I see the problem, it is when I must inject *manually* the dependency for a bean or component isolated of others. — Manuel Jordan, Oct 03 '14 at 16:02

Trying to generate error about Spring's @Autowired field injection for JUnit

2 Answers2