Chapter 11. Introduction to EJB injection in Servlets

This tutorial aims at showing how EJBs can be injected in a Servlet. In this tutorial we build an EAR file which contains a EJB module (jar file) and a web module (war file).

Take a look at the META-INF/application.xml file:

			
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE application PUBLIC
	"-//Sun Microsystems, Inc.//DTD J2EE Application 1.3//EN"
	"http://java.sun.com/dtd/application_1_3.dtd">
<application>
  <display-name>jboss-ejb3-tutorial-ejb_injection</display-name>
  <description>Enterprise application showing injection of EJB in Servlet</description>
  <module>
    <web>
      <web-uri>jboss-ejb3-tutorial-enterprise_webapp.war</web-uri>
      <context-root>/jboss-ejb3-tutorial-enterprise_webapp</context-root>
    </web>
  </module>
  <module>
    <ejb>jboss-ejb3-tutorial-enterprise_ejb3app.jar</ejb>
  </module>
</application>

EJB module:

The EJB module in this tutorial consists of a EJB3 SLSB. Take a look at org.jboss.tutorial.enterprise_app_ejb_injection.bean.CalculatorBean:

				
@Stateless(name="calculator")
@Remote(CalculatorRemote.class)
@Local(CalculatorLocal.class)
public class CalculatorBean implements CalculatorRemote, CalculatorLocal
{
...

We will be using this bean in the servlet for performing the add and subtract operations.

Important

When a EJB packaged in a jar file is deployed as part of an EAR, the default jndi-name for the business-remote interface will be of the form EARName/BeanName/remote. Similarly the local business-remote will have the default jndi-name of the form EARName/BeanName/local.

Web module:

The web module consists of a index.html and a servlet org.jboss.tutorial.enterprise_app_ejb_injection.servlet.CalculatorActionServlet. Take a look at the WEB-INF/web.xml which configures the index.html as the welcome page and also maps the servlet.

				
 <servlet>
      <servlet-name>CalculatorActionServlet</servlet-name>
      <servlet-class>org.jboss.tutorial.enterprise_app_ejb_injection.servlet.CalculatorActionServlet</servlet-class>
 </servlet>

<!-- The servlet and jsp page mappings -->
<servlet-mapping>
   <servlet-name>CalculatorActionServlet</servlet-name>
   <url-pattern>/CalculatorAction</url-pattern>
</servlet-mapping>

<welcome-file-list>
	<welcome-file>index.html</welcome-file>
</welcome-file-list>

The org.jboss.tutorial.enterpise_app_ejb_injection.bean.CalculatorLocal will be injected in the org.jboss.tutorial.enterprise_app_ejb_injection.servlet.CalculatorActionServlet using the @EJB annotation:

				
private CalculatorLocal calculator;

/**
 * Injecting the EJB
 */
@EJB(name = "calculator")
public void setCalculator(CalculatorLocal calculator)
{
   this.calculator = calculator;
}

Important

For the injection to take place in a web module, your web.xml should use the 2.5 version of the web-app xsd:

						
<web-app version="2.5"
	xmlns="http://java.sun.com/xml/ns/javaee"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

Building and Running

Note

To build and run the example, make sure you have installed JBoss 5.x. See the Section 1.1, “JBoss Application Server 5.x” for details.

From the command prompt, move to the "enterprise_app_ejb_injection" folder under the Section 1.3, “Set the EJB3_TUTORIAL_HOME”

Ant Users:

Make sure your JBossAS-5.x is running

	
$ ant

This will deploy the ear into the JBossAS-5.x server ("default" configuration).

To access the servlet, open a web browser and enter http://localhost:8080/jboss-ejb3-tutorial-enterprise_webapp. This will bring up a page where you can enter two number and either click on Add or subtract.

Maven Users: Make sure the AS is not running.

$ mvn clean install -PRunSingleTutorial

This will create the EAR in the target folder of the tutorial. Copy this EAR to the deploy folder of JBossAS-5.x and start the server (if it's already not started). Then follow the steps mentioned above, to access the servlet from the web browser.