Java EE6 & Wicket - Article #4 - Adding JPA Persistence And EJB Support

Welcome to the 4th in a series of detailed articles on Java EE6 & Wicket. If you haven’t already, please read the following previous articles before continuing.

1. http://jeff-schwartz.blogspot.com/2011/03/java-ee6-wicket.html
2. http://jeff-schwartz.blogspot.com/2011/03/java-ee6-wicket-article-1-requirements.html
3. http://jeff-schwartz.blogspot.com/2011/03/java-ee6-wicket-article-2-creating.html
4. http://jeff-schwartz.blogspot.com/2011/03/java-ee6-wicket-article-3-generating.html

Data Access

The GuestBook Web application we are building must access the data from the guest table in the guestbook database which we created together in the 2nd article. The goal of this article is to provide access to the database using JPA and Enterprise Java Bean (EJB).

NetBeans built in tooling supports creating Entity beans from an existing database table. We will use this feature to generate an Entity bean from the guest table.

NetBenas built in tooling also supports creating an EJB. We will use this feature to create a stateless session bean with JPA access functionality which is commonly referred to as a facade and in the next article we will inject an instance of this facade into our Wicket pages that will allow them to access the guestbook database.

One of the new features of EE6 EJB is, unlike EE5, it doesn’t require we implement interfaces when access is local (meaning from the same container).

First, we will generate our Entity bean from the guest table and then we will create the EJB to provide access to the database. So lets get started.

Create A New Entity Class From A Database Table

In the Projects panel right click on the Source Packages item and select New | Other which will open the New File window. In the Categories list select Persistence and in File Type select Entity Classes from Database and then click the Next button.

1. Expand the Data Source dropdown and select New Data Source to open the Create Data Source window. Enter guestbook for the JNDI Name and from the Database Connection dropdown list select the database connection which we created in the previous article and click OK.

   

2. If prompted for the password enter the password you created when you installed MySQL and click OK.

3. From the list of Available Tables select the guest table and then click the Add button to add it to the Selected Table list and click the Next button.

   

4. Enter com.myapp.entities for the Package name and click the Next button.

   

5. Select java.util.List for the Collection Type and then click the Finish button.

The result of the above steps is NetBeans created Guest.java POJO with JPA annotations and placed it in the com.myapp.entities package. NetBeans also created the JPA configuration file persistence.xml. If you fully expand the project node in the Projects panel you will see the following:

If you open the Guest.java file you will see that it contains standard JPA annotations, getters and setters and numerous named queries. While you have the file open we will apply a change to its ‘toString’ method which we will use when be  build at the application:

• If it isn’t already, open Guest.java and replace the ‘toString’ method (it is located at the bottom of the file) with the following:
• @Override
  public String toString() {
      return firstName + " " + lastName;
  }

We will make use of this method i

Create The EJB

1. In the Projects panel right click on Source Packages and select New | Other to open the New File window.

2. From Categories select Persistence and from File Types select Session Beans For Entity Classes and click the Next button.

3. Select com.myapp.entities.Guest from Available Entity Classes and click the Add button to add it to the list of Selected Entity Classes and then click the Next button.

4. Enter com.myapp.sessionbeans for the Package and click the Finish button. Notice how we didn’t create any interfaces in this last step.

   

The result of the above steps is NetBeans created 2 classes in the com.myapp.sessionbeans package, AbstractFacade.java and  GuestFacade.java.

• AbstractFacade.java is an abstract class that implements generalized functionality.
• GuestFacade.java, a subclass of AbstractFacade.java, provides Guest.java type specific behavior and is annotated with @Stateless marking it as a stateless session bean.

One more thing to do and then we are done. Fully expand Server Resources in the Projects panel and open the sun-resources.xml file. If you set up your MySQL installation to require a password then make sure the Password’s property tag in this file has your correct password. If it doesn’t add your password and save the file. I’ve modified mine as follows:

<property name="Password" value="admin"/>

In the next article we will build out the Wicket parts of GuestBook and use the features provided by the JavaEE Inject Library which we added to our project in the 3rd article to inject the GuestFacade.java session bean into our Wicket pages. Stay tuned!