So far this series has covered simple IoC dependency injection as well as bean initialization with @PostConstruct and constructor injection.

In this part we will introduce container managed contextual scopes to Voodoo DI.

A scope defines the life-cycle of a bean, allowing state to be preserved and or shared across multiple interactions. DI frameworks offer a fast variety of build-in and add-on scopes, such as @RequestScoped, @SessionScoped, @ApplicationScoped, etc…

So far Voodoo DI simply maps interfaces, supertypes and the target type directly to the concrete implementations.

//Map Interfaces and Supertypes to concrete implementation.
private final Map types = new ConcurrentHashMap<>();
...
public  T instance(Class clazz) {
    T newInstance = null;
    try {
      Constructor constructor = types.get(clazz).getConstructor(new Class[]{});
      newInstance = constructor.newInstance(new Object[]{});
      processFields(clazz, newInstance);
    } catch (Exception ex) {
      Logger.getLogger(Voodoo.class.getName()).log(Level.SEVERE, null, ex);
      throw new RuntimeException(ex);
    }
    return newInstance;
  }
...

Continue reading Understanding Dependency Injection – Part 3 Contexts →