Using OpenSessionInViewInterceptor to avoid LazyInitializationException

Question

First I need to acknowledge the fact that I'm new to EJB, JPA and Spring, so many of the things I believe as true could be wrong.

I'm building an EJB application where there's an stateless session bean used to retrieve many JPA (Hibernate) entities. The problem, which I believe is a widespread problem, is that I cannot traverse the relationships of those entities when the stateless returns any instance. I get the dreaded LazyInitializationException. In many cases I found that using eager fetching I could avoid the exception, but this felt more like a workaround than a real fix. After lots of googling, I found that (since I'm using spring) probably the most intrusive way to accomplish this was using OpenSessionInViewInterceptor.

Reading this looks like it's easy to use, but I can't map the files mentioned in the article. One possible explanation is that I'm using Spring 3, so the names for the files might have changed. I do have a spring3app-servlet.xml where beans are being declared. I also have a web.xml where filters are set (this file I believe that was used with spring 2.0, but it still works with 3.0).

Further searching made me realize that the filenames weren't my only concern, since I don't have any SessionFactory bean, which I believe it's necessary for this to work. This lead me to search info about the SessionFactory bean.

That search made me realize that I probably need .hbm.xml files. I'm not sure if those files are really needed, or if they where a requisite for legacy hibernate-spring versions.

tl;dr: I want an OpenSessionInViewInterceptor. Do I need a SessionFactory Bean? Do I need .hbm.xml files? Where can I find all the information to set this up?

Edit:

Maybe the solution is using OpenSessionInViewFilter. I'm trying to use it but it still fails with the same exception. I'm reading this in search of a fix.

Answer 1

First, if you're going for an all out JPA solution, you should use OpenEntityManagerInViewFilter. Which does something similar to OpenSessionInViewInterceptor, but for JPA

As for the session bean, you will always get a LazyInitializationException since the object is loaded in a different session. Lazy fields are only accessible in the current http request. If you access the field in another http request you will get a LazyInitializationException.

(by the way hibernate define a http request as "Session". But a Spring session covers multiple http request. Yes this is confusing).

What you can do to avoid the LazyInitializationException is:

1. Reload the session bean. For example:

   MyObject objectFromDb = objectDAO.find(objectFromSession.getId());

2. Or initialize the field when you set the field in a session bean:

   Hibernate.initialize(field);

(don't forget to recurse over all children fields)

---

Ok, since this is the same session, you do need a OpenEntityManagerInViewFilter/OpenSessionInViewInterceptor, which will create an Hibernate session for each Http request. So put an entry in your web.xml:

    <filter>
        <filter-name>JpaFilter</filter-name>
        <filter-class>org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>JpaFilter</filter-name>
        <url-pattern>*.jsp</url-pattern>
    </filter-mapping>

The OpenEntityManagerInViewFilter is similar. Also make sure that your "entityManagerFactory" bean is injected in your filter.