Question

I have my JSF Handler defined in request scope as follows

public class JsfHandler {
  private List<ManagedBean>  managedBeanList;   // managed bean List in session scope
}

    <managed-bean>
        <managed-bean-name>jsfHandler</managed-bean-name>
        <managed-bean-class>com.test.JsfHandler</managed-bean-class>
         <managed-bean-scope>request</managed-bean-scope>
        <managed-property>
            <property-name>managedBeanList</property-name>
            <value>#{managedBeanList}</value>
        </managed-property>
      </managed-bean>

I have a session scoped JSF managed bean list in JSF defined as follows.

   <managed-bean>
      <managed-bean-name>managedBeanList</managed-bean-name>
      <managed-bean-class>java.util.ArrayList</managed-bean-class>
      <managed-bean-scope>session</managed-bean-scope>
   </managed-bean>

Approach 1:

managedBeanList.clear();
managedBeanList.addAll(service.getResultList());  
// assuming service.getResultList() would return a new ArrayList();

Approach 2:

managedBeanList =  service.getResultList();
FacesContext.getCurrentInstance().getExternalContext().getSessionMap().put("managedBeanList",managedBeanList);

We are currently using approach 1.

Is approach 2 correct? Is there is any advantage in terms of memory usage when Java Garabage collector is called in appraoch 2.

Answer 1

Neither is correct. That list has to be a property of a session scoped managed bean. You should avoid manually fiddling with the session map as much as possible.

Neither of the one is more “GC-friendly” than the other. In approach 1 you end up with an unreferenced instance to the list as returned by service.getResultList(). In approach 2 you end up with an unreferenced instance of the list which was previously referenced by managedBeanList. In both cases the GC has to do the same job: cleaning an unreferenced instance.