How to use @Inject in CDI managed beans compliant with SonarQube rule S3306

Question

I'm working on a JSF project using CDI. We are using SonarQube to manage the code quality. One of the issues that popped up after running a scan on our project is S3306: "Constructor injection should be used instead of field injection".

It was triggered by injects we are using in our beans, for example:

@Named
@ViewScoped
public class AccountsController extends AbstractController<Account> {

  @Inject
  private AccountsFacade accountsFacade;

  public AccountsController() {
    super(Account.class);
  }

  ...
}

Injected are facades like:

@Stateless
public class AccountsFacade extends AbstractFacade<Account> {

  @PersistenceContext(unitName = "...")
  private EntityManager entityManager;

  public AccountsFacade() {
    super(Account.class);
  }

  ...
}

The info on this issue provided by SonarQube:

Field injection seems like a tidy way to get your classes what they need to do their jobs, but it's really a NullPointerException waiting to happen unless all your class constructors are private. That's because any class instances that are constructed by callers, rather than instantiated by the Spring framework, won't have the ability to perform the field injection.

Instead @Inject should be moved to the constructor and the fields required as constructor parameters.

This rule raises an issue when classes with non-private constructors (including the default constructor) use field injection.

The suggested solution:

class MyComponent {

  private final MyCollaborator collaborator;

  @Inject
  public MyComponent(MyCollaborator collaborator) {
    Assert.notNull(collaborator, "MyCollaborator must not be null!");
    this.collaborator = collaborator;
  }

  public void myBusinessMethod() {
    collaborator.doSomething();
  }
}

Since managed beans are created using a constructor with no arguments, is there any way to comply with the SonarQube rule?

Edit: I think this is relevant: we are using CDI. I'm not sure if the previous link (Oracle documentation) applies here.

Edit 2: I just tried the suggested solution after I've read documentation on WELD injection points. But that gives me this error:

WELD-001435: Normal scoped bean class ...AccountsController is not proxyable because it has no no-args constructor

Edit 3: The error in edit 2 is indeed (see comments at the question) caused by the @Inject of the AccountsController in an other controller. See also the answer.

Answer 1

The suggested solution does work for injecting @Stateless classes into CDI beans with Payara 4.1.1 163. I have been experiencing problems with GlassFish 4.1 though.

Additionally, when you apply this solution when injecting beans into other beans like:

@Named
@ViewScoped
public class OtherController extends AbstractController<Other> {

  private final AccountsController accountsController;

  @Inject
  public OtherController(AccountsController accountsController) {
    Assert.notNull(accountsController, "accountsController must not be null!");
    this.accountsController = accountsController;
  }

}

.. you'll get this error (as mentioned in edit 2 of the question):

WELD-001435: Normal scoped bean class ...AccountsController is not proxyable because it has no no-args constructor

N.B. AccountsController was modified as suggested.

I resolved this issue by using OmniFaces Beans:

@Named
@ViewScoped
public class OtherController extends AbstractController<Other> {

  private final AccountsController accountsController;

  public OtherController() {
    this.accountsController = Beans.getInstance(AccountsController.class);
  }

}

... or, for something completely different, you could also just suppress the warning on your (CDI) managed beans:

@SuppressWarnings("squid:S3306")