Question

The Object is the logged in user with some objects related to him. I would like to keep the traffic on the database to a minimum. I need a proper solution to do this. I use JSP-Code without Scriptlets, with Servlets and I get the object through JPA. I hope you understand what I mean.

Answer 1

You can store your object to the HttpSession via the methods setAttribute(...) and retrieve it via getAttribute(...)

So your code (in a servlet) would look something like that:

final String CURRENT_USER_KEY = "CURRENT_USER";

EntityManager em; // somewhere initialized
Integer userid; //  somewhere initialized

HttpSession session =  httpServletRequest.getSession();
User user = session.getAttribute(CURRENT_USER_KEY);

if(user == null){
  User user = em.find(User.class, userId);
  session.setAttribute(CURRENT_USER_KEY, user);
}

// perform further actions on your user