Could not instantiate bean : Constructor threw exception; nested exception is java.lang.NullPointerException

Question

package baseDao;

public interface BaseDao {

    public void create(Object obj);
    public void delete(Object obj);
    public void update(Object obj);
    public void         


        

Answer 1

The problem is here:

@Autowired
private  SessionFactory usermanagementSessionFactory;
private  Session session = usermanagementSessionFactory.getCurrentSession();

The sessionFactory needs to be autowired, but this only happens after construction. Construction involves the second line being executed - which uses the unset factory. Hence you get a null pointer exception.

Even though your class doesnt have a constructor, construction of an instance can still thow an exception as a result of field initialisation, as in this case.

Answer 2

Move the session initialization to below method

@PostConstruct
public void init(){
      session = usermanagementSessionFactory.getCurrentSession();
}

Answer 3

You are trying to initialize session object, when usernameSessionFactory object is not initialized yet.

In a class, all Spring @Autowired objects are initialized just after the construction of the instance of such class is done.

private  Session session = usermanagementSessionFactory.getCurrentSession();

But if an instance decleared in a way like the above code, will be initialized earlier than construction, in a way that they can even be used as parameters of construction.

@Autowired
private  SessionFactory usermanagementSessionFactory;
private  Session session;

@PostConstruct
public void init() {
    session = usermanagementSessionFactory.getCurrentSession();
}

Above code, will initialize session object after the construction, which means usermanagementSessionFactory is ready and not null.

Hopefull it helps..