Lazy Injection with javax.inject.Provider 📎
javax.inject.Provider is the minimalistic version of the javax.enterprise.inject.Instance interface. In fact Instance inherits from Provider
For on-demand injection of components / resources inject them as Provider:
@Model
public class Index {
@Inject
Provider<Boundary> boundary;
public String getMessage() {
return boundary.get().message();
}
}
The injected component is unaware about the laziness:
@Stateless
public class Boundary {
public String message() {
return "Good morning";
}
}
Instance comes with additional functionality: see also Interfaces on Demand with CDI and EJB 3.1
[See also an in-depth discussion in the "Real World Java EE Patterns--Rethinking Best Practices" book (Second Iteration, "Green Book"), page 235 in, chapter "Plugin"]
See you at Java EE Workshops at Munich Airport, particularly at: Effective Java EE 7!