Leveraging Stateful EJBs with extended Persistence Context and flexible transaction demarcations to achieve results similar to an Unsynchronized Persistent Context (JPA 2.1)

CustomerEditorFacade.java

package com.abhirockzz.conversationalee;

import com.abhirockzz.conversationalee.entity.Customer;
import java.util.Date;
import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import javax.ejb.Remove;
import javax.ejb.Stateful;
import javax.ejb.TransactionAttribute;
import javax.ejb.TransactionAttributeType;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.PersistenceContextType;

@Stateful
@TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED)
public class CustomerEditorFacade{
 
  @PersistenceContext(type = PersistenceContextType.EXTENDED)
  EntityManager em;
  
  @Inject //this won't work in Java EE 5
  Principal authenticatedUser;
  
  private Customer customer;
  
  @PostConstruct
  public void init(){
      System.out.println("CustomerEditorFacade created at " + new Date().toString());   
  }
  
  @PreDestroy
  public void destroy(){
      System.out.println("CustomerEditorFacade destroyed at " + new Date().toString());   
  }
  
  //step 1
  public void updateCity(String custID, String city){
    String custID = authenticatedUser.getName(); //assume we have an authenticated principal which is the same as the customer ID in the Database
    Customer customerFromDB = em.find(Customer.class, Integer.valueOf(custID)); //obtain a 'managed' entity
    customerFromDB.setCity(city); //no need to call em.persist
    customer = customerFromDB; //just switch references
    
    //Customer state will NOT be pushed to DB
  }

  //step 2
  public void updateEmail(String email){
    customer.setEmail(email); //not pushed to DB yet
  }
  
  @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
  public void save(){
    //dummy method to trigger transaction and flush EM state to DB
  }
  
  @Remove
  public void finish(){
    //optional method to provide a way to evict this bean once used
    //not required if this is session scoped
  }

}