This demo application showcases the support Oracle Application Server 10g
10.1.3.1 has for the EJB 3.0 specification, demonstrating support for the
optional use of EJBHome, and how to migrate EJB components to EJB 3.0 without
breaking the old EJB 2.x clients. This example utilizes a Stateful EJB.
EJB 3.0 greatly simplifies development of EJB applications by removing a lot
of the complexities developers faced in preview versions. Creating a simple
stateful EJB using EJB 2.1 requires a bean class, two interfaces and a
deployment descriptor. The component interface (remote and/or local) and home
interfaces have to extend javax.ejb.EJBObject and javax.ejb.EJBHome
respectively and the bean class has to implement the javax.ejb.SessionBean
interface.
With EJB 3.0, many of these requirements have been relaxed:
The bean class may be a plain
java class (POJO)
The EJB interface may be a pure
java interface (POJI)
You no longer must provide an
EJBHome interface
Annotations may be used instead
of an XML deployment descriptor
We will create a basic shopping cart EJB to demonstrate a simple stateful
EJB using EJB 3.0. This example will have an optional home interface.
Stateful Session Bean using EJB 3.0
Here is the remote interface for
Cart EJB.
Note that this is a pure Java
interface and it does not extend EJBObject.
package oracle.ejb30;
import java.util.Collection;
import javax.ejb.Remote;
@Remote
public interface Cart {
public void addItem(String item);
public void removeItem(String item);
public Collection getItems();
}
>Here is the code for the bean class. The EJB is a plain Java class that implements its business interface.
package oracle.ejb30;
import java.util.ArrayList;
import java.util.Collection;
import javax.ejb.Init;
import javax.ejb.Stateful;
@Stateful
@RemoteHome(CartHome.class)
public class CartBean implements Cart {
private ArrayList items;
@Init
public void initialize() {
items = new ArrayList();
}
public void addItem(String item) {
items.add(item);
}
public void removeItem(String item) {
items.remove(item);
}
public Collection getItems() {
return items;
}
}
Any method annotated with @Init annotation is invoked when an EJB 2.1 client invokes a create method on stateful session bean instance. The @RemoteHome(CartHome.class) annotation marks the home
interface for the bean to be oracle.ejb30.CartHome.
The EJB Client
EJB
client code is dramatically simplified in EJB 3.0. The client no longer requires
the retrieval of the EJB home interface from JNDI, and does not have to
specifically create a bean instance by invoking create on the home interface.
Clients can now simply and directly invoke a method on the EJB.
However with EJB being utilized in distributed systems, the luxury of changing
deployed client code may not be afforded to all applications. Therefore it may
be required to support existing client code bases which use the old style
lookup based on the retrieval of the EJBHome object and the calling of the
create method to obtain an instance of the bean.
Here
is a snippet from client code that accesses the EJB
public class CartClient {
public static void main(String[] args) throws Exception {
Context context = new InitialContext();
System.out.println("Looking up Cart");
CartHome cartHome =
Cart cart = cartHome.create();
System.out.println("Adding items to cart");
cart.addItem("Item1");
cart.addItem("Item2");
System.out.println("Listing cart contents");
Collection items = cart.getItems();
for (Iterator i = items.iterator(); i.hasNext();) {
String item = (String) i.next();
System.out.println(" " + item);
}
}
}
Prerequisites
What you need to know
You should be familiar with these
technologies: EJB in general and some insight into the EJB 3.0
specification
etc - all necessary files to
package the application
lib - holds the application
archives that could be deployed
doc - the How-to document and
Javadoc's
javadoc - the javadoc of the
different source files
how-to-ejb30-compatibility-ejb2x.html
- this How-to
page
src - the source of the demo
ejb - contains the sample SFSB
code
client - contains application client
code
Configuring the
Environment
Environment Configuration
Make sure the following environment variables are defined.
%ORACLE_HOME% - The directory where you
installed OC4J.
%JAVA_HOME% - The directory where your JDK
is installed
%PATH% - includes %ORACLE_HOME%
/ant/bin
Starting up Oracle
Application Server 10g 10.1.3
Start OC4J stand alone using the following command after you make the above changes.
>%ORACLE_HOME%/bin/oc4j -start
If you are using an OracleAS managed install, start using the following command after you make the above changes.
> %ORACLE_HOME%/opmn/bin/opmnctl startall
4. Generate, Compile, and Deploy the Application
Ant 1.6.2 is shipped with OC4J and you have to set your PATH environment variable to $ORACLE_HOME/ant/bin. 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 ant-oracle.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 for OC4J standalone:
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)
If you are using OracleAS managed install then you have appropriately change the following properties beside changing oc4j.admin.user and oc4j.admin.password for your managed OC4J instance in OracleAS install.
opmn.host: the hostname/IP where OracleAS is running (default localhost)
opmn.port: OPMN request port (default 6003) for the OracleAS install
oc4j.instance: admin user name (default oc4jadmin)
You have to uncomment appropriate deployer.uri in the ant-oracle.properties based on your environment i.e. a single instance OC4J or a clustered OC4J instance/group managed by OPMN.
You have to make changes in jndi.properties such as provider.url, principal and credential appropriate to your environment. If you are using OracleAS install, you have to use provider.url in the following format: opmn:ormi://localhost:6003:home/ejb30compatibility.
Build the Application
In the top-level %HOWTO_HOME% directory, type the command:
>ant
You should now have the newly created ejb30compatibility.ear in your %HOWTO_HOME%/lib
directory.
This command would also attempt to deploy the application if the build is
successful. It will first test whether OC4J is running.
Deploy the Application
You can also deploy the application separately by using the following
command. Make sure the %ORACLE_HOME% environment variable is defined. In
the top-level %HOWTO_HOME% directory, type the command:
>ant deploy
Run the
Application
You can run the sample as follows:
>ant run
Now go back to the console where you started OC4J and you will see output
generated by the Cart EJB.
[java] Looking up Cart
[java] Adding items to cart
[java] Listing cart contents
[java] Item1
[java] Item2
Summary
In this document, you should have:
Learned to develop a Stateful
Session Bean using EJB 3.0 with an optional EJBHome interface
Deployed and executed a simple
stateful session bean in the Oracle Application Server 10g 10.1.3.1 without
breaking compatibility with EJB 2.x clients
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