Accessing injected dependency in managed bean constructor causes NullPointerException

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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("[email protected]");
}

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