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Listing 16.3 Spring-enabled stateless PlaceBid EJB
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@Stateless(name = "PlaceBid") public class PlaceBidBean extends AbstractStatelessSessionBean implements PlaceBid { private BidServiceBean bidService; public PlaceBidBean() { }
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Figure 16.2 You can combine the power of Spring and EJB 3 by developing a Springenabled session bean. You can use the declarative transaction, security, and web services features of EJB 3 with the POJO injection and JpaTemplate features of Spring.
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Extends Spring class Defines POJO
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protected void onEjbCreate() { Retrieves bean bidService = (BidServiceBean) getBeanFactory().getBean("bidService"); }
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public Long addBid(String userId, Long itemId, Double bidPrice) { return bidService.addBid(userId, itemId, bidPrice); } Uses bean
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Combining the power of EJB 3 and Spring
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In listing 16.3 the bean class extends the Spring support class in the (org.springframework.ejb.support.AbstractStatelessSessionBean) package b. Note that the EJB bean cannot inherit from another bean or class because Java does not support multiple inheritances. The BidServiceBean POJO is defined as an instance variable c. When a PlaceBid EJB instance is created, the onEjbCreate method is invoked and an instance of BidServiceBean is retrieved d and stored in the POJO that we defined c. The business method delegates the task to the BidServiceBean when it is invoked e. Now you must be wondering how the Spring bean factory is created and how the Spring configuration is provided. Under the covers, when an EJB instance is created it performs a JNDI lookup to locate the path (java:comp/env/ejb/BeanFactoryPath) for the bean factory. Therefore, you have to define the following environment variable in the EJB deployment descriptor for the EJB:
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<session> <display-name>PlaceBid</display-name> <ejb-name>PlaceBid</ejb-name> <env-entry> <env-entry-name>ejb/BeanFactoryPath</env-entry-name> <env-entry-type>java.lang.String</env-entry-type> <env-entry-value>/actionBazaar-service.xml</env-entry-value> </env-entry> </session>
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The env-entry-value for the ejb/BeanFactoryPath environment variable is set to /actionBazaar-service.xml. After you package the EJB and Spring configuration file, you should be able to invoke the EJB, and internally it will use Spring beans to perform the intended task.
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16.3.2 Using session beans from Spring beans
Perhaps by now you ve grown fond of EJB 3 and worked with it in your application. Some of your other application modules happen to use Spring. What you d like to do is reuse the business logic you ve developed in your EJBs by incorporating it into your Spring component, as shown in figure 16.3. In this section we ll show you how to inject instances of session beans into your Spring beans. Suupose you have a session bean named ItemManager:
@Stateless(name = "ItemManager") public class ItemManagerBean implements ItemManager {
Figure 16.3 You can access a session bean from a Spring bean and reuse the business logic.
EJB 3 and Spring
public Item addItem(String title, String description, Double initialPrice, String sellerId) { ... return item; } }
You want to use the ItemManager session bean in the ItemServiceBean, which is a Spring POJO (see listing 16.4).
Listing 16.4 A Spring POJO that uses an injected stateless session bean
public class ItemServiceBean implements ItemService { private ItemManager itemManager;
public ItemServiceBean() { }
Specifies instance variable for EJB
// Setter injection of ItemManagerEJB public void setItemManager(ItemManager itemManager) { this.itemManager = itemManager; }
Injects setter
public Long addItem(String title, String description, Double initialPrice, String sellerId) { Item item = itemManager.addItem(title, description, initialPrice, sellerId); return item.getItemId(); Invokes EJB } }
method
In listing 16.4 you will see no difference in using a POJO because EJB 3 session beans are also POJOs. In the Spring bean, we ve defined an instance variable for the EJB interface ItemManager b and we use setter injection to inject an instance of the EJB object c and invoke a method on the EJB d. You must be wondering where the actual magic happens. We aren t doing a JNDI lookup, and we re not using the @EJB annotation to inject an EJB object. The real magic occurs in wiring the EJB in the Spring configuration, as shown in listing 16.5. Spring has factory classes for wiring invocation of EJB 2.1 session beans. Fortunately, you don t need those and you can use the JndiObjectFactoryBean.
Summary
Listing 16.5 A Spring POJO that uses an injected stateless session bean
<bean id = "itemManager" class = "org.springframework.jndi.JndiObjectFactoryBean"> <property name = "jndiName" value = "java:comp/env/ejb/ItemManager"/> </bean> Defines bean
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