java.lang.NullPointerException in HibernateUtil

Question

I am getting following exception. The exception always comes back to the line:

      Session session = HibernateUtil.getDefaultSession().openSession();

Here is a trimmed version of the stacktrace:

SEVERE: Servlet.service() for servlet [jsp] in context with path [/examAdmin] threw exception [java.lang.NullPointerException] with root cause
java.lang.NullPointerException
    at dao.AddCartDAO.deleteUnknownCartProduct(AddCartDAO.java:105)
    at org.apache.jsp.index_jsp._jspService(index_jsp.java:396)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)

My HibernateUtil looks like--

    public class HibernateUtil {
        private static SessionFactory factory;

        @SuppressWarnings("deprecation")
       private HibernateUtil() {
       try {
            factory = new Configuration().configure().buildSessionFactory();
           } catch (Throwable ex) {
           System.err.println("Failed to create sessionFactory object." + ex);
         throw new ExceptionInInitializerError(ex);
        }
  }

public static SessionFactory getDefaultSession() {
       return factory;
}

And my DAO looks like something

 public void deleteUnknownCartProduct(String uid, String status) {
  Session session = HibernateUtil.getDefaultSession().openSession();
  Transaction tx = null;
  try {
     tx = session.beginTransaction();
     String hql = "Delete AddCart a where a.userid=:userid and a.status=:status";
     Query query = session.createQuery(hql);
     query.setParameter("userid", uid);
     query.setParameter("status", status);
     query.executeUpdate();
     tx.commit();
} catch (HibernateException e) {
     if (tx != null)
     tx.rollback();
     e.printStackTrace();
} finally {
     session.close();
}
}

I have been trying numerous different things and Have tried as stackoverflow suggested however and still get same null-pointer at same line of code..

My folder structure:

pls show deleteUnknownCartProduct method , and what in line : AddCartDAO.java:105 ? — xyz
– xyz, Commented Jun 23, 2017 at 12:31
@sbjavateam line-105 Session session = HibernateUtil.getDefaultSession().openSession(); — Created Bylucky
– Created Bylucky, Commented Jun 23, 2017 at 12:40
@sbjavateam, actually i'm new in hibernate so i'm not able to figure it out what are you saying, so please can you explain — Created Bylucky
– Created Bylucky, Commented Jun 23, 2017 at 12:48

Stephen C · Accepted Answer · 2017-06-23 14:09:24Z

You say that the exception is thrown in this line:

   Session session = HibernateUtil.getDefaultSession().openSession();

Since HibernateUtil.getDefaultSession is a static method, this means that getDefaultSession() is returning null.

Then we look at getDefaultSession() and it is simply returning the the value of factory. ThisgetDefaultSession implies that factory is null. How come? Because your code is not initializing it!!

I can see you are attempting to initialize it in a constructor. But that can only work if you call the constructor. And you don't!

A better solution is to use a static method to do the initialization; e.g.

public class HibernateUtil {
    private static SessionFactory factory = initFactory();

    @SuppressWarnings("deprecation")
    private static initFactory() {
        try {
            return new Configuration().configure().buildSessionFactory();
        } catch (Throwable ex) {
            System.err.println("Failed to create sessionFactory object." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getDefaultSession() {
        return factory;
    }
}

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