I'm trying to inject a DAO as a managed property.
public class UserInfoBean {
private User user;
@ManagedProperty("#{userDAO}")
private UserDAO dao;
public UserInfoBean() {
this.user = dao.getUserByEmail("test@gmail.com");
}
// Getters and setters.
}
The DAO object is injected after the bean is created, but it is null
in the constructor and therefore causing NullPointerException
. How can I initialize the managed bean using the injected managed property?
Injection can only take place after construction simply because before construction there's no eligible injection target. Imagine the following fictive example:
UserInfoBean userInfoBean;
UserDao userDao = new UserDao();
userInfoBean.setDao(userDao); // Injection takes place.
userInfoBean = new UserInfoBean(); // Constructor invoked.
This is technically simply not possible. In reality the following is what is happening:
UserInfoBean userInfoBean;
UserDao userDao = new UserDao();
userInfoBean = new UserInfoBean(); // Constructor invoked.
userInfoBean.setDao(userDao); // Injection takes place.
You should be using a method annotated with @PostConstruct
to perform actions directly after construction and dependency injection (by e.g. Spring beans, @ManagedProperty
, @EJB
, @Inject
, etc).
@PostConstruct
public void init() {
this.user = dao.getUserByEmail("test@gmail.com");
}
来源:https://stackoverflow.com/questions/10196982/accessing-injected-dependency-in-managed-bean-constructor-causes-nullpointerexce