Correct Usage of Stateful Session Bean in EJB - jsf

Question

I am trying to construct a test website that display various information about a student with JSF 2.0, EJB 3.1 and JPA 2.0.
After a student login, the student can browse different pages for displaying different kind of information, which is what a usual registration management system does. Say displaying a timetable according to enrollment information in one page, and display the assignments in another page. Information that will be displayed include attributes of the student, mapped entities like registered course, assignment submitted etc.
At first, I tried to create a stateless bean and get the information required for each page, and change some attributes of student
#Entity
public class Student{
#Id
private String sid;
private String address;
#ManyToMany
private List<Assignment> submittedAssignments;
#ManyToMany
private List<Course> courses;
}
#Stateless
#LocalBean
public class studentDao {
#PersistenceContext(unitName="PU")
private EntityManager em;
public Student getStudent(String sid){
return em.find(Student.class, sid);
}
public List<Course> getCoursesByStudent(String sid){
return em.find(Student.class, sid).getCourses();
}
public List<Assignment> getAssignmentsByStudent(String sid){
return em.find(Student.class, sid).getSubmittedAssignments();
}
#TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
public void ChangeAddress(String sid, String newAddress){
em.find(Student.class, sid).setAddress(newAddress);
}
#TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
public void SubmitAssignment(String sid, Assignment submittedAssignment){
}
//Some more methods, just list a few for illustration.
}
#ManagedBean
#SessionScoped
public class LoginSession{
private String sid;
//getter
public login(String sid){
//probably will need password validation later, so I have to connect to db and check the password.
this.sid=sid;
}
}
#ManagedBean
#RequestScoped
public class AssignmentBean{
#EJB
private StudentDao studentDao;
#ManagedProperty(value="#{loginSession}")
private LoginSession session;
public List<Assignment> getAssignments(){
return studentDao.getAssignmentsByStudent(session.sid);
}
}
assignment.xhtml:
<h:datatable value="#{assignmentBean.assignments}"></h:datatable>
And then, I find it quite tedious to pass student from managed bean to stateless ejb, retrieve student, again and again, then return only a part of information to ManagedBean for display, therefore I think I can do it like this.
#Stateful
#LocalBean
public class studentDao {
#PersistenceContext(unitName="PU", type=PersistenceContextType.EXTENDED)
private EntityManager em;
private Student currentStudent;
public void login(String sid){
//didn't make a password, just type sid and done.
currentStudent = em.find(Student.class, sid);
}
public Boolean getLoggedIn(){
return currentStudent != null;
}
public Student getCurrentStudent(){
return currentStudent;
}
#TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
public void ChangeAddress(String newAddress){
currentStudent.setAddress(newAddress);
}
#TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
public void SubmitAssignment(Assignment submittedAssignment){
}
}
#ManagedBean
#SessionScoped
public class LoginSession{
#EJB
private StudentDao studentDao;
public login(String sid){
studentDao.login(sid);
}
}
assignment.xhtml:
<h:datatable value="#{loginSession.studentDao.currentStudent.submittedAssignments}"></h:datatable>
As the currentStudent lives with the extended persistence context, I can retrieve the information directly. And I do not have to pass SID to EJB again and again for each operation, also applies for finding that student again and again as it is already there managed.
I am not sure if it is an abuse of #Stateful bean as the pages had been a large group of conversations, unlike the common "shopping cart" example where user can choose a lot of orders, make payment, then commit all database changes after validation and user confirm.
Please comment on the above SFSB usage whether it is an abuse of SFSB and why if it is an abuse, or which one of the above two designs is better (or suggest another if both were bad as I am the first time writing a web application starting from scrap but a few books from Apress, those started with Pro whatever, EJB3, JPA, JSF, Java EE 6 with glassfish etc).
Thank you.

Answer 1

If you use stateful session beans, the EJB container manages state on behalf of your client, so there is no need to pass around an ID: It's more comfortable.
In your case it's OK.
Generally speaking, consider these items:
Stateless services are sometimes a little bit easier to test: If you write a test case, you do not have to consider the side-effects on the state.
If your stateful session bean holds cached data, you have to handle cache invalidation.
If your session bean is #Remote: If client and server are not on the same JVM, each method call requires marshalling, and goes over the network.
If you have lots of stateful sessions which consume resources on the server side: You already have two Lists there, and their number and their content will most likely grow over the time. Using a stateless setup, you can design an application where the state is only managed in the browser, for example.
If someone else is using your comfortable stateful API, and you must change it later, you will have endless discussions.
For these reasons I always prefer the stateless setup using data transfer objects. But again, in your case it's OK.