In the first part of this series I introduced basic IoC functionality. In this part we will cover @PostConstruct methods and Constructor Injection.

Consider the following scenario:

public class Car {
  @Inject
  private Engine engine;  

  public Car() {
    engine.initialize();  
  }
  ...
}  

Since Car has to be instantiated prior to field injection, the injection point engine is still null during the execution of the constructor, resulting in a NullPointerException.

This problem can be solved either by JSR-330 Dependency Injection for Java constructor injection or JSR 250 Common Annotations for the Java @PostConstruct method annotation.
Continue reading Understanding Dependency Injection – Part 2 PostConstruct and Constructor Injection →