嵌套豆的春季依赖注入

Question

I'm fighting with Spring Dependency Injection and nested beans: There are two beans and one of them is nested in the other. When inspecting the outer bean, I can see, that the inner bean isn't injected.

The main class:

public class Main {

  public static void main(String[] args) {
    AnnotationConfigApplicationContext ctx
      = new AnnotationConfigApplicationContext("org.acme");

    MyService myService = ctx.getBean(MyService.class);
    // do something with myService
  }
}

The outer bean:

@Component
public class MyService {

  @Inject // javax.inject.Inject
  private MyDao dao;

  public MyService() {
    System.out.println(dao);
  }
}

The inner bean:

@Component
public class MyDao {

  public MyDao() {
    System.out.println("dao is alive");
  }
}

There is no error when starting the application, but I see null getting printed out by the constructor of MyService and dao is alive . I had the same issue when trying with a @Configuration class. It seems like the outer beans depedencies won't be injected.

Thx!

Answer 1

As fields and methods parameters are injected after the constructor is called, you cannot use injected member variables in the constructor.

reference

Answer 2

I made it work with constructor injection .

@Component
public class MyService {

  private MyDao dao;

  @Inject // javax.inject.Inject
  public MyService(MyDao dao) {
    System.out.println(dao);
  }
}