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Spring and Java EE 5 (PART 2)

Simplicity and power combined

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In the first part of this article you learned how Java EE 5 has simplified enterprise application development by adopting a POJO programming model and making use of Java 5 metadata annotations. You also discovered how the Spring Framework version 2.0 integrates with Java Persistence API (JPA) and makes it simple to use from enterprise Java applications.

In this second part, you will learn how you can integrate the Spring Framework with EJB 3 components and to exploit Spring's declarative transaction features with Java EE applications. Finally we'll discover how Java EE application servers provide seamless management of Spring components from their JMX-enabled management consoles.

Using Spring and EJB 3
As we discussed in Part 1 of this article, EJB 3 greatly simplifies development of EJB components. Spring's Pitchfork project implements part of the EJB 3 specification, for example, enabling use of @Stateless or @Resource annotations with Spring beans. It also lets developers use @Stateless annotations in a web container.

You can mix and match EJB 3 and Spring components to leverage the power of both frameworks. For example, you can combine such features as statefulness, pooling, clustering, declarative security, Web Service feature, and message-driven beans of EJB 3 with AOP, POJO injection , template-based data, and resource access support provided by Spring.

Injecting Session Beans
You may remember from our earlier discussion that Java EE 5 lacks support for POJO injection. If you want to use an EJB from a helper class of your Web or EJB module then injection isn't supported and unfortunately you have to resort to JNDI lookup. Note that application server vendors will provide proprietary extensions to support POJO injection.

However you can use Spring to simplify and use its powerful dependency injection mechanism to inject an instance of a session bean. This will help your applications to port between application servers. Let us dive down and see an example.

The code examples that follow are taken from my recently published book, EJB 3 in Action, published by Manning Publications.

Assume that you have a session bean named ItemManager that you will use in the ItemServiceBean, which is a Spring POJO, as shown below:

public class ItemServiceBean implements ItemService {

private ItemManager itemManager;
public ItemServiceBean() {
}

// Setter injection of ItemManagerEJB
public void setItemManager(ItemManager itemManager) {
this.itemManager = itemManager;
}

public Long addItem(String title, String description,
Double initialPrice, String sellerId) {
Item item = itemManager.addItem(title, description,
initialPrice, sellerId);
return item.getItemId();
}
}

As you can see, we are using setter injection to inject an instance of ItemManager EJB object and invoke a method on the EJB.

By now you must be wondering where the actual magic happens? We're not doing a JNDI lookup and not using the @EJB injection (that we discussed in Part 1) to inject the session bean object. The real magic occurs through wiring in the EJB through the Spring configuration.

Let's assume that the Spring Bean uses a remote business interface of ItemManager EJB and retrieves it using a Spring 2.0 simplified jee-jndi lookup as follows:

<jee:jndi-lookup id = "itemManager" jndi-name = "ejb/ItemManager" resource-ref = "true"/>

Note that we are using setter injection in ItemServiceBean to inject an instance of ItemManager EJB and we must wire the ItemManager EJB as follows:

<bean id = "itemService" class = "actionbazaar.buslogic.ItemServiceBean">
<property name = "itemManager" ref = "itemManager"/>
</bean>

Remember from our discussion in part 1 of the article that EJB 3 Session beans are POJOs and interfaces are POJI. So there's no difference between invoking EJB3 session beans with either a remote or local interface if your Spring beans and EJBs are collocated in the same container, and the configuration is identical for both local and remote session beans. If your Session bean is in a remote container you'll have to provide the JNDI properties such has provider URL, principal, and credentials to invoke the remote bean.

Spring-Enabled Session beans
We 'll examine another interesting case of integration where you can leverage the power of Spring in an EJB 3-based application. You can use Spring in your session beans (both stateless and stateful) and message-driven beans (MDB). I'll demonstrate the use of Spring beans from an EJB 3 stateless session bean. If you've used Spring with EJB 2 you may remember that the framework provides several factory classes for such integration. You can use those abstract classes with EJB 3 session beans to enable access to the Spring bean factory. As these factory classes require they have to implement the onEjbCreate() method in your EJB 3 bean class to access a Spring bean.

Below is the same EJB 3 example (PlaceBid EJB) transformed into a Spring-enabled stateless session bean. Here the PlaceBid EJB acts as a façade and delegates the actual business logic to the PlaceBidServiceBean.

@Stateless(name = "PlaceBid")
public class PlaceBidBean extends AbstractStatelessSessionBean
implements PlaceBid {

private BidServiceBean bidService;
public PlaceBidBean() {
}

protected void onEjbCreate() {
bidService =
(BidServiceBean) getBeanFactory().getBean("bidService");
}

public Long addBid(String userId, Long itemId, Double bidPrice) {
return bidService.addBid(userId, itemId, bidPrice);
}
}

More Stories By Debu Panda

Debu Panda is a Director of Product Management at Oracle Corporation. He is lead author of the EJB 3 in Action (Manning Publications) and Middleware Management (Packt). He has more than 20 years of experience in the IT industry and has published numerous articles on enterprise Java technologies and has presented at many conferences. Debu maintains an active blog on enterprise Java at http://debupanda.blogspot.com.

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