Writing Enterprise Applications with J2EE First lesson

1
WritingEnterprise Applications with J2EE(First
lesson)

• Alessio Bechini
• June 2002
• (based on material by Monica Pawlan)

2
A Simple Session Bean

• Example Thin-Client Multitiered Application
• Path and ClassPath Settings
• J2EE Application Components
• Create the HTML Page
• Create the Servlet
• Create the Session Bean
• Compile the Session Bean and Servlet

• Start the J2EE Application Server
• Start the Deploy Tool
• Deploy Tool
• Assemble the J2EE Application
• Verify and Deploy the J2EE Application
• Run the J2EE Application
• Updating Component Code

3
Thin-Client Multitiered Application
4
J2EE Download Contents

• The typical download has the J2EE application
  server, Cloudscape database, a Web server using
  secure socket layer (SSL) also known as HTTP over
  HTTPS, development and deployment tools, and the
  Java APIs for the Enterprise.

5
PATH and CLASSPATH

• Path Settings
• Unix
• ../J2EE/jdk1.2.2/bin
• ../J2EE/j2sdkee1.2.1/bin
• Windows replace / with \
• Class Path Settings
• Unix
• ../J2EE/j2sdkee1.2.1/lib/j2ee.jar
• Windows replace / with \

6
J2EE Appl. Components

• The J2EE specification defines the following
  application components
• Application client components
• Enterprise JavaBeans components
• Servlets and JavaServer Pages components (also
  called Web components)
• Applets

7
Interacting Components

• The session bean executes in the J2EE
  application server.

• Data flows between the browser and the session
  bean.

8
HTML Code

• ltHTMLgt
• ltBODY BGCOLOR "WHITE"gt
• ltBLOCKQUOTEgt
• ltH3gtBonus Calculationlt/H3gt
• ltFORM METHOD"GET"
• ACTION"BonusAlias"gt
• ltPgt
• Enter social security Number
• ltPgt
• ltINPUT TYPE"TEXT" NAME"SOCSEC"gtlt/INPUTgt
• ltPgt

• Enter Multiplier
• ltPgt
• ltINPUT TYPE"TEXT" NAME"MULTIPLIER"gtlt/INPUTgt
• ltPgt
• ltINPUT TYPE"SUBMIT" VALUE"Submit"gt
• ltINPUT TYPE"RESET"gt
• lt/FORMgt
• lt/BLOCKQUOTEgt
• lt/BODYgt
• lt/HTMLgt

9
Servlet Duties

• At run time, the servlet code does the following
• Retrieves the user data
• Looks up the session bean
• Passes the data to the session bean
• Upon receiving a value back from the session
  bean, creates an HTML page to display the
  returned value to the user.

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Servlet Code (I)

• import javax.servlet.
• import javax.servlet.http.
• import java.io.
• import javax.naming.
• import javax.rmi.PortableRemoteObject
• import Beans.
• public class BonusServlet extends HttpServlet
• CalcHome homecalc
• public void init(ServletConfig config) throws
  ServletException
• //Look up home interface
• try
• InitialContext ctx new InitialContext()
• Object objrefctx.lookup("calcs")
• homecalc (CalcHome)PortableRemoteObject.na
  rrow(objref,CalcHome.class)
• catch (Exception NamingException)
• NamingException.printStackTrace()

11
Servlet Code (II)

• public void doGet (
• HttpServletRequest request, HttpServletResponse
  response)
• throws ServletException, IOException
• String socsec null
• int multiplier 0 double calc 0.0
• PrintWriter out
• response.setContentType("text/html")
• String title "EJB Example"
• out response.getWriter()
• out.println("ltHTMLgtltHEADgtltTITLEgt")
• out.println(title)
• out.println("lt/TITLEgtlt/HEADgtltBODYgt")
• try
• Calc theCalculation
• //Get Multiplier and Soc.Sec. Info
• String strMultrequest.getParameter("MULTIPLIE
  R")
• Integer integerMult new Integer(strMult)
• multiplier integerMult.intValue()
• socsec request.getParameter("SOCSEC")

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Servlet Code (III)

• //cont. for public void doGet (
• //Display Data
• out.println("ltH1gtBonus Calculationlt/H1gt")
• out.println("ltPgtSoc Sec " socsec "ltPgt")
• out.println("ltPgtMultiplier " multiplier
  "ltPgt")
• out.println("ltPgtBonus Amount " calc
  "ltPgt")
• out.println("lt/BODYgtlt/HTMLgt")
• out.close()
• public void destroy()
• System.out.println("Destroy")

13
Interfaces of a EJBean

• This picture shows how the servlet and session
  bean application components work as a complete
  J2EE application once they are assembled and
  deployed.
• The container is the interface between the
  session bean and the low-level platform-specific
  functionality that supports the session bean.
  The container is created during deployment.

14
Creating a session bean

• A session bean represents a transient
  conversation with a client. If the server or
  client crashes, the session bean and its data
  are gone.
• In contrast, entity beans are persistent and
  represent data in a database. If the server or
  client crashes, the underlying services ensure
  the entity bean data is saved.
• Because the enterprise bean performs a simple
  calculation at the request of BonusServlet, and
  the calculation can be reinitiated in the event
  of a crash, it makes sense to use a session bean
  in the current example.

15
CalcHome

• BonusServlet does not work directly with the
  session bean, but creates an instance of its
  home interface.
• The home interface extends EJBHome and has a
  create method for creating the session bean in
  its container.
• CreateException is thrown if the session bean
  cannot be created, and RemoteException is thrown
  if a communications-related exception occurs
  during the execution of a remote method.

• package Beans
• import java.rmi.RemoteException
• import javax.ejb.CreateException
• import javax.ejb.EJBHome
• public interface CalcHome extends EJBHome
• Calc create() throws CreateException,
  RemoteException

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Calc

• When the home interface is created, the J2EE
  application server creates the remote interface
  and session bean.
• The remote interface extends EJBObject and
  declares the calcBonus method for calculating
  the bonus value.
• This method is required to throw
  javax.rmi.RemoteException, and is implemented by
  the CalcBean class.

• package Beans
• import javax.ejb.EJBObject
• import java.rmi.RemoteException
• public interface Calc extends EJBObject
• public double calcBonus(int multiplier, double
  bonus)
• throws RemoteException

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CalcBean

• The session bean class implements the SessionBean
  interface and provides behavior for the calcBonus
  method.
• The setSessionContext and ejbCreate methods are
  called in that order by the container after
  BonusServlet calls the create method in CalcHome.

• package Beans
• import java.rmi.RemoteException
• import javax.ejb.SessionBean
• import javax.ejb.SessionContext
• public class CalcBean implements SessionBean
• public double calcBonus(int multiplier, double
  bonus)
• double calc (multiplierbonus)
• return calc
• //These methods are not described here
• public void ejbCreate()
• public void setSessionContext(SessionContext
  ctx)
• public void ejbRemove()
• public void ejbActivate()
• public void ejbPassivate()
• public void ejbLoad()
• public void ejbStore()

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Compiling Instructions

• Session Bean
• Unix
• !/bin/sh
• cd ../J2EE
• J2EE_HOME../J2EE/j2sdkee1.3.1
• CPATH.J2EE_HOME/lib/j2ee.jar
• javac -d . -classpath "CPATH" Beans/CalcBean.java
  Beans/CalcHome.java Beans/Calc.java
• Windows
• cd \home\monicap\J2EE
• Set J2EE_HOME..\J2EE\j2sdkee1.3.1
• set CPATH.J2EE_HOME\lib\j2ee.jar
• javac -d . -classpath CPATH Beans/CalcBean.java
  Beans/CalcHome.java Beans/Calc.java

• Servlet
• Unix
• .. javac -d . -classpath "CPATH"
  BonusServlet.java
• Windows
• .. javac -d . -classpath "CPATH"
  BonusServlet.java

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J2EE Application Server Deploy Tool

• You need to start the J2EE application server to
  deploy and run the example.
• type j2ee -verbose
• Note Sometimes the J2EE server will not start if
  Outlook is running.
• To assemble and deploy the J2EE application, you
  have to start the deploy tool.
• type deploytool
• Note If a memory access error is encountered
  when starting deploytool, add an environment
  variable called JAVA_FONTS and set the path to c
  \ltfont directorygt, e.g. c\winnt\fonts.

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The Deploy Tool GUI
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Assemble the J2EE Application

• Assembling a J2EE application involves creating
  a new application, and adding the application
  components to it, according to the following
  steps
• Create a new J2EE application
  (BonusApp.ear).
• Create a new enterprise bean
  (CalcBean.jar).
• Create a new web component
  (Bonus.war).
• Specify JNDI name for the enterprise bean
  (calcs).
• Specify the Root Context for the J2EE application
  
  (BonusRoot).

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Create J2EE Application

• J2EE components are assembled into J2EE
  application Enterprise Archive (EAR) files.
• From File menu Select New Application.

• New Application dialog box
• Fill the data about the application file name
  (BonusApp.ear) and the application display name
  (BonusApp), specifying the ditectory where you
  want to place the application EAR file.
• The GUI looks as shown.

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Create Session Bean (I)

• Enterprise beans (entity and session beans) are
  bundled into a Java Archive (JAR) file.

• File menu Select New Enterprise Bean. The New
  Enterprise Bean Wizard starts and displays an
  Introduction dialog box.Click Next.
• EJB JAR dialog box Specify the jar display name
  (CalcJar, within BonusApp), and possibly other
  ancillary info.
• Add Files to Contents dialog box
• Calc.class, CalcHome.class,
• CalcBean.class.
• The GUI looks as shown.
• Go to the next step

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Create Session Bean (II)

• In this step, make sure the following information
  is selected
• classname CalcBean
• Home interface Beans.CalcHome
• Remote interface Calc
• Bean type Session and Stateless
• Specify the display name (the name that appears
  when when the JAR file is added toBonusApp in the
  Local Applications window)
• Description e.g., This JAR file contains the
  CalcBean session bean.
• No further info is needed for the bean..

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Creation of the Session Bean

• Once the session bean has been created, the GUI
  looks as shown.

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Create Web Component (I)

• Web components (servlets, or JSP technology) are
  bundled into a WAR file.

• File menu Select New Web Component. The New
  Web Component Wizard starts.
• Provide the name to be displayed for the WAR, and
  then add contents
• First, bonus.html
• And then the servlet class,BonusServlet.class
• The GUI looks as shown.
• Go to the next step.

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Create Web Component (II)

• At the next step of the wizard, select the
  BonusServlet as a servlet component.
• Now, the GUI looks as shown.

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Component Aliases

• At the component aliases step of the wizard,
  type BonusAlias. This is the same alias name
  you put in the ACTION field of the HTML form
  embedded in the bonus.html file.
• Now, the GUI looks as shown.

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Componentss Deployment Summary
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Specify JNDI Name

• Before you can deploy the BonusApp application
  and its components, you have to specify the JNDI
  name BonusServlet uses to look up the CalcBean
  session bean.

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Specify Root Context
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Verify Specification Compliance
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Deploy the J2EE Appl.
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Run the J2EE Appl.

• The web server runs on port 8000 by default. To
  open the bonus.html page point your browser to
• http//localhost8000/BonusRoot/bonus.html
• which is where the Deploy tool put the HTML file.