JavaWithBreakfast: OCEJBCD - 3- Accesing Session Beans

OCEJBCD (SCBCD) - 1Z0-895 - Enterprise JavaBeans Developer Certification

3.1. Understand the purpose and role of JNDI in relation to EJB components

JNDI : Java naming directory
Binding - assigning a name to an EJB object which can be used later.
Lookup - looking up and getting an object of EJB.

3.2. Configure JNDI environment properties
http://docs.oracle.com/javaee/6/tutorial/doc/gipjf.html#girgn

global

java:global[/application name]/module name/enterprise bean name[/interface name]

module

java:module/enterprise bean name/[interface name]

app

java:app[/module name]/enterprise bean name[/interface name]

3.3. Use JNDI to look up a resource
Accessing an enterprise bean can be done by dependency injection or JNDI lookup.

Example using JNDI lookup:
ExampleRemote example = (ExmapleRemote) InitialContext.lookup("java:global/myApp/ExampleRemote");

3.4. Write code that receives a resource reference through injection

The annotations for inject a resource are:
@EJB - used to inject other EJB reference (on fields or on methods).
@Resource - used to inject datasource or singleton services like sessionContext, timerService etc.

We will see a complete code example in the followings sections (3.5- 3.7) and step by step we will create a javaEE application. This simple application is compound by:

Web client project : with a servlet and JSP
EJB server project :with sessionEJB and its interface.

The purpose will be create an application that allows a user selecting one color from a dropdown list. When submitting the selection a servlet will be executed and will call an EJB bean method. The bean method will return the color that will be displayed in the screen.

3.5. Create a session bean client

We are going to define an stateless session bean with a method that will evaluate a number of options and it will return the hex code corresponding to one color:

If input is 1 -- > color blue
If input is 2 -- > color red
If input is 3 -- > color yellow

	package example;

	import javax.ejb.EJB;
	import javax.ejb.Stateless;

	@Stateless
	@EJB(name="java:global/ExampleBeans/TestBean", beanInterface=TestBeanLocal.class)
	public class TestBean implements TestBeanLocal {

	/**
	* Default constructor.
	*/
	public TestBean() {
	// TODO Auto-generated constructor stub
	}

	public String testColor(String color) {
	String colorStyle = "#ffffff";

	switch (color) {
	case "1":
	colorStyle = "#0000ff";
	break;
	case "2":
	colorStyle = "#ff0000";
	break;
	case "3":
	colorStyle = "#ffff00";
	break;
	}
	return colorStyle;

	}
	}

view raw TestBean.java hosted with ❤ by GitHub

3.6. Create a session facade
http://www.oracle.com/technetwork/java/sessionfacade-141285.html

Session facade provides a level of abstraction between the client and the business object. It manages the interactions between client and business services.

For the session bean defined in the previous section we will define an interface, that will be used by the client to access to our bean.

	package example;

	import javax.ejb.Local;
	import javax.ejb.Remote;

	@Local
	public interface TestBeanLocal {

	public String testColor(String color);
	}

view raw TestBeanLocal.java hosted with ❤ by GitHub

3.7. Use dependency injection to locate an EJB

Now, we will have to define the client that will call the bean (Servlet and JSP).
JSP

	<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
	pageEncoding="ISO-8859-1"%>
	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
	<html>
	<head>
	<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
	<title>Insert title here</title>
	<style>
	p {
	border: 1px solid grey;
	padding: 10px;
	margin: 30px;
	}
	</style>
	</head>
	<body>
	<form action="myColor">
	<p>
	SELECT ONE COLOR <select id="list" name="color">
	<option value="0" ${color == '0' ? 'selected' : ''}>SELECT



	<option>
	<option value="1" ${color == '1' ? 'selected' : ''}>BLUE</option>
	<option value="2" ${color == '2' ? 'selected' : ''}>RED</option>
	<option value="3" ${color == '3' ? 'selected' : ''}>YELLOW</option>
	</select> <input type="submit" value="SUBMIT" /> <br />
	</p>
	<p>
	<input type="text" value="${colorStyle}" /> <br />
	</p>
	<p>
	<input type="color" value="${colorStyle}" />
	</p>

	</form>
	</body>
	</html>

view raw colorSelector.jsp hosted with ❤ by GitHub

Servlet class
The servlet class will have a method doGet, that will be called everytime the button submit is clicked.
The dependency injection to locate the bean is applied by annotation:
@EJB
TestBeanLocal colorBean;

	package color;

	import java.io.IOException;

	import javax.ejb.EJB;
	import javax.servlet.RequestDispatcher;
	import javax.servlet.ServletException;
	import javax.servlet.annotation.WebServlet;
	import javax.servlet.http.HttpServlet;
	import javax.servlet.http.HttpServletRequest;
	import javax.servlet.http.HttpServletResponse;

	import example.TestBean;
	import example.TestBeanLocal;

	/**
	* Servlet implementation class ColorSelectorServlet
	*/
	@WebServlet("/myColor")
	public class ColorSelectorServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	@EJB
	TestBeanLocal colorBean;
	/**
	* Default constructor.
	*/
	public ColorSelectorServlet() {
	// TODO Auto-generated constructor stub

	}

	/**
	* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
	* response)
	*/
	protected void doGet(HttpServletRequest request,
	HttpServletResponse response) throws ServletException, IOException {
	// TODO Auto-generated method stub
	String color = request.getParameter("color");

	String colorStyle = "#ffffff";

	if (color != null) {
	colorStyle = colorBean.testColor(color);//call the bean method
	}

	request.setAttribute("colorStyle", colorStyle);
	request.setAttribute("color", color);
	RequestDispatcher rd = request
	.getRequestDispatcher("/colorSelector.jsp");
	rd.forward(request, response);
	}

	/**
	* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
	* response)
	*/
	protected void doPost(HttpServletRequest request,
	HttpServletResponse response) throws ServletException, IOException {
	// TODO Auto-generated method stub
	}

	}

view raw ColorSelectorServlet.java hosted with ❤ by GitHub

After deploying our application (web and EJB) in the server. When entering this url in the browser: http://localhost:8080/ColorWeb/myColor, the page is open:

When a color is selected the corresponding hex code and color are shown in the screen

Note: The details about environment configuration are described in this post : http://javawithbreakfast.blogspot.com/2015/11/configuring-ejb-environment.html
OCEJBCD (SCBCD) - 1Z0-895 - Enterprise JavaBeans Developer Certification

Saturday, 21 November 2015

OCEJBCD - 3- Accesing Session Beans

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