Writing Enterprise Applications with J2EE Fifth lesson

1
WritingEnterprise Applications with J2EE(Fifth
lesson)

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

2
Using JavaBeans with EJBs

• Rationale for using JavaBeans
• We can put a JavaBean between the JSP page and
  CalcBean session bean to obtain the Model, View,
  Controller (MVC) separation.
• MVC is a design pattern the Model provides the
  application business logic, the View is its
  screen presentation, and the Controller is an
  object that manages user interactions with the
  View.
• In the previous example, the HTML and JSP pages
  both provide the View and manage user
  interactions with the data (Controller). The
  entity and session bean (BonusBean and CalcBean)
  are the application objects (or Model).

3
Separation of View and Controller

• In the current example, we are going to use a
  JSP page for the screen presentation (View), a
  JavaBean to manage what happens when the user
  interacts with the View (Controller), and the
  entity and session beans for the application
  objects (Model).
• Separating the Controller from the View lets the
  JavaBean serve as a wrapper for the session bean
  and gives the example a much cleaner MVC
  separation.
• An application that uses clear design patterns
  is easier to update, maintain, and manage.

4
Steps towards MVC Separation

• Create bonus.jsp
• Create the JavaBeans Class
• Bean Properties
• Remove the WAR File
• Create New WAR FIle
• Verify and Deploy the J2EE Application
• Run the J2EE Application

5
Merging bonus.html and Bonus.jsp

• In the previous example, the HTML form calls the
  JSP page when the user clicks the Submit button
  on the HTML page.
• Another way to create the user interface is with
  one single JSP page that includes the HTML form,
  JSP scriptlets, and JSP-specific tags for
  interacting with the JavaBean. When the JSP page
  loads, the HTML form is displayed and the
  scriptlet and JSP-specific tags are executed.
• After the user enters some data and clicks the
  Submit button, the HTML form is redisplayed and
  the scriptlet and JSP-specific tags execute again
  with the supplied data. This is because the
  ACTION parameter for the HTML form cursively
  calls the JSP page itself

• ...
• lt!--ACTION parameter calls this page--gt
• ltFORM METHOD"GET" ACTION"bonus.jsp"gt
• ...

6
Create Bonus.jsp

• The code for bonus.jsp is now simplified,
  because the code to look up the session bean
  and calculate the bonus is now in the JavaBean.
• The first part of the file contains the HTML code
  to create the form. The code to pass the HTML
  form data to the JavaBean is in the second part
  of the file.

• ltHTMLgt
• ltBODY BGCOLOR "WHITE"gt
• ltHEADgt ltTITLEgtBonus Calculationlt/TITLEgt lt/HEADgt
• ltBLOCKQUOTEgt
• ltH3gtBonus Calculationlt/H3gt
• lt!--ACTION parameter calls this page--gt
• ltFORM METHOD"GET" ACTION"bonus.jsp"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
• ...

7
Bonus.jsp (cont.)

• ...
• lt!--Scriptlet and JavaBeans Tags start here --gt
• ltjspuseBean id "jbonus" class "JBonusBean"/gt
• lt! String sMult, ssec gt
• lt
• sMult request.getParameter("MULTIPLIER")
• ssec request.getParameter("SOCSEC")
• gt
• ltjspsetProperty name "jbonus"
  property"strMult" value"ltsMultgt"/gt
• ltjspsetProperty name "jbonus"
  property"socsec" value"ltssecgt"/gt
• Social security number retrieved
• ltjspgetProperty name"jbonus" property"socsec"/gt
  
• ltPgt
• Bonus Amount retrieved
• ltjspgetProperty name"jbonus" property"bonusAmt"
  /gt
• ltPgt

8
Specify the JavaBean

• The following HTML tag specifies the JavaBean
  being used in this example.
• The id parameter defines an alias to use to
  reference the JavaBean, and the class parameter
  specifies the JavaBeans class.
• In this example the id is jbonus and the class
  is JBonusBean.
• ltjspuseBean id "jbonus"
• class "JBonusBean"/gt

9
Get the Data

• The following JSP scriptlets retrieve the
  user-supplied data from the HTML form input
  fields.
• The multiplier is stored in the sMult String
  variable, and the social security number is
  stored in the ssec String variable.

• lt! String sMult, ssec gt
• lt
• sMult request.getParameter("MULTIPLIER")
• ssec request.getParameter("SOCSEC")
• gt

10
Pass Data to the JavaBean

• The following tags set two properties in the
  JavaBean. A property is a private field in the
  JavaBean class.
• The first line uses the jspsetProperty name tag
  to set the strMult field in the JBonusBean class
  (aliased by the jbonus id) to the value stored
  in the sMult variable.
• The second line performs a similar operation for
  the socsec field in the JBonusBean class.
• The value"ltssecgt" expression sends the data
  contained in the ssec variable to the socsec
  field in the JavaBean.

• ltjspsetProperty name "jbonus"
  property"strMult" value"ltsMultgt"/gt
• ltjspsetProperty name "jbonus"
  property"socsec" value"ltssecgt"/gt

11
Retrieve Data from the JavaBean

• Retrieving data from a JavaBean is similar to
  sending data to it. You use the jspgetProperty
  name tag and indicate the property (private
  field) whose data you want to get.
• The following getProperty name tag retrieves the
  data stored in the socsec private field of the
  JBonusBean class (aliased by the jbonus id).

• Social security number retrieved
• ltjspgetProperty name"jbonus" property"socsec"/gt

12
Create the JavaBeans Class

• A Java bean looks just like any ordinary
  Javaclass. But to be a bean, a Java class must
  follow a set of simple naming and design
  conventions. Because beans follow the JavaBeans
  specification, they can be accessed and managed
  by other programs and tools that follow the same
  conventions.
• In the previous example with bonus.jsp, HTML tags
  and JSP scriptlets are used to get and set data
  in the private fields of the JBonusBean class.
  This is possible because JBonusBean follows
  the JavaBeans naming and design conventions.

13
The JBonusBean class (I)

• import javax.naming.
• import javax.rmi.PortableRemoteObject
• import Beans.
• public class JBonusBean
• private String strMult, socsec, message
• private double bonusAmt
• CalcHome homecalc
• public JBonusBean()
• try
• InitialContext ctx new InitialContext()
• Object objref ctx.lookup("calcs")
• homecalc (CalcHome)PortableRemoteObject.na
  rrow(objref,
• 
  CalcHome.class)
• catch (javax.naming.NamingException e)
  e.printStackTrace()

14
The JBonusBean class (II)

• public double getBonusAmt()
• if(strMult ! null)
• Integer integerMult new Integer(strMult)
• int multiplier integerMult.intValue()
• try
• double bonus 100.00
• Calc theCalculation homecalc.create()
• Bonus theBonus theCalculation.calcBonus(
  multiplier, bonus, socsec)
• Bonus record theCalculation.getRecord(so
  csec)
• bonusAmt record.getBonus()
• socsec record.getSocSec()
• catch (javax.ejb.DuplicateKeyException e)
  
• message e.getMessage()
• catch (javax.ejb.CreateException e)
  e.printStackTrace()
• catch (java.rmi.RemoteException e)
  e.printStackTrace()
• return this.bonusAmt
• else this.bonusAmt 0 this.message
  "None." return this.bonusAmt
• public String getMessage() return
  this.message

15
Bean Properties

• Bean properties define the data accessible to
  other programs and tools through get and set
  methods..
• Properties are actually private class fields that
  should always be private and only accessible
  through get and set methods.
• The following code segment shows the private
  properties for the JBonusBean class. This class
  has a corresponding getltpropertygt method for
  each field and corresponding setltpropertygt
  methods for the strMult and socsec fields.

• public class JBonusBean
• private String strMult, socsec, message
• private double bonusAmt
• ...

16
JBonusBean constructor

• The JBonusBean constructor looks up the session
  Bean.

• public JBonusBean()
• try
• InitialContext ctx new InitialContext()
• Object objref ctx.lookup("calcs")
• homecalc (CalcHome)PortableRemoteObject.narro
  w(
• objref, CalcHome.class)
• catch (javax.naming.NamingException e)
• e.printStackTrace()

17
Set Methods

• Setter methods set properties (private fields) to
  specified values. setSocsec and setStrMult are
  in charge ofr setting the socsec and strMult
  private fields (JavaBean properties).
• The values used to set the socsec and strMult
  properties come from the setProperty name tags
  in the JSP page. The J2EE server uses the
  information in the following setProperty name
  tags to locate the corresponding set methods in
  the JBonusBean (aliased by the jbonus id)
• Similar observations apply to get methods.

• ltjspsetProperty name "jbonus"
  property"strMult
• 
  value"ltsMultgt"/gt
• ltjspsetProperty name "jbonus"
  property"socsec"
• 
  value"ltssecgt" /gt