Improve your life Through Science and Art: JPA: Thread-safety when injecting EntityManager

One way to fix this is to inject EntityManagerFactory instead. EntityManagerFactory is guaranteed to be thread-safe. For example:

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public class EMTestServlet extends HttpServlet {   //This field injection is thread-safe   @PersistenceUnit   private EntityManagerFactory emf;      protected void doGet(HttpServletRequest request,              HttpServletResponse response)   throws ServletException, IOException {   EntityManager em = emf.createEntityManager();   //work with em   } }

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