Implementing POJOs with EJB 3 - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 393

well as arbitrary values such as strings and integers. There are also other useful
features, such as its support for AOP . In comparison, EJB 3 dependency injection is
a convenient way for EJB s to access JNDI objects but lacks many of those features
provided by Spring dependency injection. Ideally, we should be able to use the
two dependency mechanisms together and leverage each of their strengths.
The good news is that there is a way to integrate Spring and EJB 3 dependency
injection. We can use Spring's bean factory mechanism to create and wire
together POJO s and use EJB 3 dependency injection to inject the POJO s into EJB s.
Not only does this let EJB 3 applications take advantage of Spring's dependency
injection, but it can also make it easier to incorporate existing Spring code.
We need to do three things to integrate Spring and EJB dependency injection:

Expose Spring beans via JNDI when the application is initialized.

1

Annotate the session bean class to bind a JNDI name to the EntityManager
and annotate its fields to inject the POJO s using JNDI .

2

Configure a Spring JndiObjectFactoryBean to look up the EntityManager
via JNDI so that it can be injected into the repositories.

3

Let's see how to do approach this task using the PlaceOrderFacade EJB as an exam-
ple. You will learn how to use Spring to create POJO s such as PlaceOrderService
and RestaurantRepository and to then inject them into the PlaceOrderFacade
EJB . Note that this section describes some aspects of JNDI that you might be unfa-
miliar with; I had certainly never used these particular JNDI API s until I tried to do
this integration. Please bear with me as I describe all the different pieces.

Exposing Spring beans via JNDI
As you saw in section 10.1, EJB dependency injection is based on JNDI ; therefore,
if you want to inject a Spring bean into an EJB it must be accessible via JNDI . We
can do this by binding a name in the JNDI tree to a JNDI Reference . A JNDI Refer-
ence is an object that tells the JNDI implementation how to find an object that
exists outside of JNDI . As figure 10.4 shows, in this particular case the Reference
acts as a bridge between the EJB container and the Spring bean factory.
To expose a Spring bean via JNDI , we would create a Reference that contains
the name and type of a Spring bean and the name of a JNDI ObjectFactory class
that calls Spring to get the bean. When the EJB container does a JNDI lookup, it
will find the Reference and call the ObjectFactory to create the object. The
ObjectFactory will get the Spring bean by calling BeanFactory.getBean() .