Arun Gupta, Miles to go ...
Arun Gupta is a technology enthusiast, a passionate runner, and a community guy who works for Sun Microsystems.
Monday August 17, 2009
TOTD
#93
showed how to get started with Java EE 6
using NetBeans
6.8 M1 and
GlassFish v3 by
building a simple Servlet 3.0 + JPA 2.0 web
application. TOTD
#94 built upon it by using Java Server Faces 2 instead of
Servlet 3.0 for displaying the results. However we are still using a
POJO
for all the database interactions. This works fine if we are only
reading values from the database but that's not how a typical web
application behaves. The web application would typically perform all
CRUD operations. More typically they like to perform one or more CRUD
operations within the context of a transaction. And how do you do
transactions in the context of a web application ? Java EE 6 comes to
your rescue.
The EJB 3.1
specification (another new specification in Java EE 6) allow
POJO classes to be annotated with @EJB and bundled within
WEB-INF/classes of a WAR file. And so you get all transactional
capabilities in your web application very easily.
This Tip
Of The Day (TOTD) shows how
to enhance the application created in TOTD #94 and use EJB 3.1 instead
of the JSF managed bean
for
performing the business logic. There are two ways to achieve this
pattern as described below.
Lets call this TOTD #95.1
- The easiest way to back a JSF page with an EJB is to
convert the managed bean into an EJB by adding @javax.ejb.Stateless
annotation. So change the "StateList" class from TOTD #94 as
shown below:
@javax.ejb.Stateless
@ManagedBean
public class StateList {
@PersistenceUnit
EntityManagerFactory emf;
public List<States> getStates() {
return emf.createEntityManager().createNamedQuery("States.findAll").getResultList();
}
}
The change is highlighted in bold, and that's it!
The big difference this time is that the business logic is executed by an EJB in a fully transactional manner. Even though the logic in this case is a single read-only operation to the database, but you get the idea :)
Alternatively, you can use the delegate pattern in the managed bean as described below. Lets call this #95.2.
- Right-click on the project, select "New", "Session Bean
..." and create a stateless session bean by selecting the options as
shown below:
This creates a stateless session with the name "StateBeanBean" (bug #170392 for redundant "Bean" in the name). - Simplify your managed bean by refactoring all the business
logic to the EJB as shown below:
@Stateless
public class StateBeanBean {
@PersistenceUnit
EntityManagerFactory emf;
public List<States> getStates() {
return emf.createEntityManager().createNamedQuery("States.findAll").getResultList();
}
}
and
@ManagedBean
public class StateList {
@EJB StateBeanBean bean;
public List<States> getStates() {
return bean.getStates();
}
}
In fact the EJB code can be further simplified to:
@Stateless
public class StateBeanBean {
@PersistenceContext
EntityManager em;
public List<States> getStates() {
return em.createNamedQuery("States.findAll").getResultList();
}
}
The changes are highlighted in bold.
The updated directory structure looks like:
The important point to note is that our EJB is bundled in the WAR file and no additional deployment descriptors were added or existing ones modified to achieve that. Now, that's really clean :)
The next blog in this series will show how managed beans can be replaced with WebBeans, err JCDI.
Also refer to other Java EE 6 blog entries.
Please leave suggestions on other TOTD that you'd like to see. A complete archive of all the tips is available here.
Technorati: totd glassfish v3 mysql javaee6 javaserverfaces jpa2 ejb netbeans
Posted by Arun Gupta in General | Comments[1]
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