java.lang.ClassCastException with the same class object

Question

This piece of code irritates me, sometimes it working and some other times it doesn\'t !

The NamedQuery : (name = \"User.findByLogin\", query = \"SEL

Answer 1

My guess would be that you have different classloaders. The same class loaded in a different classloader is still considered different by the JVM.

To verify this, you could try to catch the exception and print/log the classloaders.

public User findByLogin(String login) {
    Query query = em.createNamedQuery("User.findByLogin");
    query.setParameter("login", login);
    Object result = null;
    try {
        result = query.getSingleResult();
        return (User) result ;
    } catch (javax.persistence.NoResultException ex) {
        return null;
    } catch (ClassCastException ex) {
        logger.info("Object classloader: " + result.getClass().getClassLoader());
        logger.info("Target class classloader: " + User.class.getClassLoader());
        if(result.getClass().getClassLoader() != User.class.getClassLoader()) {
            logger.warn("Different classloaders detected!");
        }
    }
}

As for the solution, that of course depends on the rest of your setup... To get you started, I can give you some pointers to related questions asked before. Maybe some of the answers there can be helpful to you:

• Solution for the ClassCastException due to ClassLoader issue
• ClassCastException because of classloaders?
• cast across classloader?
• ClassCastException when casting to the same class

Some of the suggested solutions include changing your classloader setup, using a common interface, or serializing/deserializing your object.