This example application
demonstrates Oracle's support for the EJB
3.0 specification using an Entity bean and
further demonstrates the use of the EntityManager API for creating and finding
bean instances. It provides an example of using the new EJB 3.0 components
from a Web application.
EJB 3.0 greatly simplifies the development of
EJBs, removing many complex development tasks. For example,
creating a simple CMP entity EJB using EJB 2.1 requires a bean class and at least two
interfaces, as well as a deployment
descriptor. The remote (or local) and home interfaces
had to extend javax.ejb.EJBObject and javax.ejb.EJBHome
interfaces respectively, and the bean class had
to implement the javax.ejb.EntityBean interface. However,
in EJB 3.0, development is greatly simplified due to the following specifications:
The bean class can be a plain java class (POJO)
No interfaces are required for an entity bean
Annotations are used for O-R Mapping
This demonstration uses the Employee entity bean to demonstrate a entity bean using EJB 3.0.
Entity
Bean example using EJB 3.0
The bean class
is a plain java class that is annotated with @Entity to mark it as an entity bean.
@Entity
@Table(name = "EMP")
public class Employee implements java.io.Serializable
{
private int empNo;
private String eName;
private double sal;
@Id
@Column(name="EMPNO", primaryKey=true)
public int getEmpNo()
{
return empNo;
}
..
}
The @Table annotation
is used to specify the table name to be used by this Entity bean.
The @Id annotation is used to mark the empNo field
as the primary key of the entity bean.
The @Column annotation is used to specify that
the empNo field is mapped to the EMPNO column in the table.
Using EntityManager API from Web Module
The javax.persistence.EntityManager API is used for creating,
finding and updating entity bean instances. Although the EJB 3.0 Early Release
Draft 2 does not mandate the use of EntityManager API from web modules, the Oracle
Application Server EJB
3.0
Preview does allow you to lookup and use an instance of EntityManager from a
web
module
(Servlet/JSP).
The EntityManager API is required to
be used within a transaction, so the web module must manually demarcate
the transaction using the UserTransaction API.
In this example,
the InsertServlet looks up the EntityManager instance
and then creates entity bean instance as follows:
ut = (UserTransaction)initCtx.lookup("java:comp/UserTransaction"); ut.begin();
Context context = new InitialContext();
Employee employee = new Employee();
employee.setEmpNo(empId);
employee.setEname(name);
employee.setSal(sal); EntityManager em = (EntityManager)context.lookup("java:comp/ejb/ejb30EMfromweb-ejb/EntityManager"); em.persist(employee); ut.commit();
Web modules can lookup the EntityManager using the JNDI binding of java:comp/ejb/<ejb-module-name>/EntityManager
Prerequisites
What you need to know
In order to complete the example application, you should
be familiar with the following:
EJB 2.1
EJB 3.0
For further information on EJB 3.0, see the following
documents on OTN:
etc - all necessary files to package the application
lib - holds the application archives that could be deployed
script - contains SQL script to create a table
doc - the How-to document and Javadoc's
javadoc - the javadoc of the different source files
how-to-ejb30-emAPIfromweb.html - this How-to page
src - the source of the demo
ejb - contains the sample entity bean code
web- contains application
2. Configure the Environment
Ensure
the following environment variables are defined:
%ORACLE_HOME% - The directory where you installed OC4J.
%JAVA_HOME% - The directory where you installed
the J2SE 5.0
Configure Database
This example is based on the EMP table from the SCOTT schema
in an Oracle database. If you do not have SCOTT schema installed in your Oracle
database, or are using a database other than Oracle, create the table usingthe table.sql script
in the %HOWTO_HOME%/scripts directory.
Configure Data Source
This example requires a DataSource to be configured to connect to the database
that contains the EMP table.
For OC4J, you must configure a datasource in the %ORACLE_HOME%/j2ee/home/config/data-sources.xml file
and point it at the schema that owns the EMP table.
An OracleAS EJB 3.0 container must
be running. Start the preview
container using the following command:
>%ORACLE_HOME%/bin/ejb30 -start
4. Generate, Compile,
and Deploy the Application
Ensure Ant 1.6.2 or above is installed on your machine and configured correctly.
On some operating systems, Ant does not currently
support the use of environment variables. If this is the case for your operating
system, please modify the common.xml file located in the
%HOWTO_HOME% directory.
Edit ant-oracle.properties (in the demodirectory) and ensure
the following properties are set to the correct values,
as indicated below:
oc4j.host: host where
OC4J is running (default localhost)
oc4j.admin.port: RMI port number
(default 23791)
oc4j.admin.user: admin user name (default oc4jadmin)
oc4j.admin.password: admin user password (default welcome)
oc4j.binding.module: website name where deployed web modules
are bound (default http-web-site)
To build the application, type the following command
from the %HOWTO_HOME% directory:
>ant
You should now have the newly created ejb30entity.ear in your
%HOWTO_HOME%/lib directory.
This command will attempt to deploy the application archive if the build is
successful. It will first test whether OC4J is running before attempting the
deployment operation.
Note that you can also deploy the application
separately .
Ensure the %ORACLE_HOME% environment variable is defined,
and from the %HOWTO_HOME%
directory, type the command:
>ant deploy
5. Run
the Application
Run
the sample by providing invoking the following URL from your favorite browser:
http://localhost:8888/ejb30EMfromweb
In this page, enter employee no, Name and Salary and then click on Add Employee button.
The InsertServlet will be invoked that will try to create
the bean instance using EntityManager API.
You will be redirected
to a success page if your record was inserted successfully. You can also
check the database table to ensure the record was created.
Summary
In this document, you should have learned how to:
Develop a simple Entity bean using EJB
3.0
Use the EntityManager API from a web module
Deploy an execute the simple Entity bean using Oracle Application
Server EJB 3.0 Preview
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