Writing Enterprise Applications with J2EE Fourth lesson

1
WritingEnterprise Applications with J2EE(Fourth
lesson)

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

2
Using JSPs instead of Servlets

• JSPs let you put segments of servlet code
  directly into a static HTML page.
• When the JSP Page is loaded by a browser, the
  servlet code executes and the application server
  creates, compiles, loads, and runs a background
  servlet to execute the servlet code segments and
  return an HTML page or print an XML report.
• This lesson changes the WAR file to use a JSP
  Page instead of BonusServlet.
• Required steps
• Create the JSP Page
• Change bonus.html
• Remove the WAR File and create a new one
• Verify, deploy and run the J2EE Application

3
Create the JSP Page

• A JSP Page looks like an HTML page with servlet
  code segments embedded between various forms of
  leading (lt) and closing (gt) JSP tags.
• There are no HttpServlet methods such as init,
  doGet, or doPost. Instead, the code that would
  normally be in these methods is embedded directly
  in the JSP Page using JSP scriptlet tags.
• The following Bonus.jsp is equivalent to
  BonusServlet.
• Note that JSP tags cannot be nested. For example,
  you cannot nest a JSP comment tag within a JSP
  scriptlet tag.

4
Bonus.jsp (I)

• ltHTMLgt
• ltHEADgt
• ltTITLEgtBonus Calculationlt/TITLEgt
• lt/HEADgt
• lt-- Comment Scriptlet for import statements lt_at_
  indicates a jsp directive --gt
• lt_at_ page import"javax.naming." gt
• lt_at_ page import"javax.rmi.PortableRemoteObject"
  gt
• lt_at_ page import"Beans." gt
• lt-- Comment Scriptlet to get the
  parameters,convert string to Integer to int for
  bonus calculation, and declare/initialize bonus
  variable. lt indicates a jsp scriptlet --gt
• lt! String strMult, socsec gt
• lt! Integer integerMult gt
• lt! int multiplier gt
• lt! double bonus gt
• lt strMult request.getParameter("MULTIPLIER")
• socsec request.getParameter("SOCSEC")
• integerMult new Integer(strMult)
  multiplier integerMult.intValue()
• bonus 100.00
• gt
• lt-- Comment Scriptlet to look up session Bean
  --gt

5
Bonus.jsp (II)

• lt-- Comment Scriptlet to create session Bean,
  call calcBonus method,
• and retrieve a database record by the social
  security number (primary key) --gt
• lt try
• Calc theCalculation homecalc.create()
• Bonus theBonus theCalculation.calcBonus(mu
  ltiplier,bonus,socsec)
• Bonus record theCalculation.getRecord(socs
  ec)
• gt
• lt-- Comment HTML code to display retrieved data
  on returned HTML page. --gt
• ltH1gtBonus Calculationlt/H1gt
• Social security number retrieved lt
  record.getSocSec() gt ltPgt
• Bonus Amount retrieved lt record.getBonus() gt
  ltPgt
• lt-- Comment Scriptlet to catch
  DuplicateKeyException --gt
• lt catch (javax.ejb.DuplicateKeyException e)
• String message e.getMessage()
• gt
• lt-- Comment HTML code to display original data
  passed to JSP on returned HTML page --gt
• Social security number passed in lt socsec gt
  ltPgt
• Multiplier passed in lt strMult gt ltPgt
• Error lt message gt

6
Comments

• The first seven lines of Bonus.jsp show straight
  HTML followed by a JSP comment.
• JSP comments are similar to HTML comments
  except they start with lt-- instead of lt!--,
  which is how they look in HTML.
• You can use either JSP or HTML comments in a JSP
  file.
• HTML comments are sent to the clients web
  browser where they appear as part of the HTML
  page, and JSP comments are stripped out and do
  not appear in the generated HTML.

7
Directives

• JSP directives are instructions processed by the
  JSP engine when the JSP Page is translated to a
  servlet.
• The directives used in this example tell the JSP
  engine to include certain packages and classes.
• Directives are enclosed by the lt_at_ and gt
  directive tags.
• Example of directives in Bonus.jsp

• lt_at_ page import"javax.naming." gt
• lt_at_ page import"javax.rmi.PortableRemoteObject"
  gt
• lt_at_ page import"Beans." gt

8
Declarations

• JSP declarations let you set up variables for
  later use in expressions or scriptlets.
• You can also declare variables within expressions
  or scriptlets at the time you use them.
• The scope is the entire JSP Page, so there is no
  concept of instance variables. That is, you do
  not have to declare instance variables to be used
  in more than one expression or scriptlet.
• Declarations are enclosed by lt! and gt.
• You can have multiple declarations.
• For example, lt! double bonus String text gt.

9
Scriptlets

• JSP scriptlets let you embed java code segments
  into the JSP page.
• The embedded code is inserted directly into the
  generated servlet that executes when the page is
  requested.
• This scriptlet uses the variables declared in the
  directives described above.
• Scriptlets are enclosed by the lt and gt
  scriptlet tags.
• Example of a scriptlet in Bonus.jsp

• lt
• strMult request.getParameter("MULTIPLIER")
• socsec request.getParameter("SOCSEC")
• integerMult new Integer(strMult)
• multiplier integerMult.intValue()
• bonus 100.00
• gt

10
Predefined Variables

• A scriptlet can use the following predefined
  variables session, request, response, out, and
  in.
• This example uses the request predefined
  variable, which is an HttpServletRequest object.
  Likewise, response is an HttpServletResponse
  object, out is a PrintWriter object, and in is a
  BufferedReader object.
• Predefined variables are used in scriptlets in
  the same way they are used in servlets, except
  you do not declare them.
• Example of use of predefined variables in
  Bonus.jsp

• lt
• strMult request.getParameter("MULTIPLIER")
• socsec request.getParameter("SOCSEC")
• ...

11
Expressions

• JSP expressions let you dynamically retrieve or
  calculate values to be inserted directly into the
  JSP Page.
• In this example, an expression retrieves the
  social security number from the Bonus entity bean
  and puts it on the JSP page.
• Example of use of expressions in Bonus.jsp

• ltH1gtBonus Calculationlt/H1gt
• Social security number retrieved lt
  record.getSocSec() gt
• ltPgt
• Bonus Amount retrieved lt record.getBonus() gt
• ltPgt

12
JSP-Specific Tags

• The JavaServer Pages 1.1 specification defines
  JSP-specific tags that let you extend the JSP
  implementation with new features and hide
  complexity from visual designers who need to
  look at the JSP page and modify it.
• The JSP example in this lesson does not use any
  JSP-specific tags.
• The JSP-specific tags defined in the 1.1
  specification are the following
• jspforward and jspinclude to instruct the JSP
  engine to switch from the current page to another
  JSP page.
• jspuseBean, jspsetProperty, and jspgetProperty
  let you embed and use JavaBeans technology inside
  a JSP Page.
• jspplugin automatically downloads the
  appropriate Java Plug-In to the client to execute
  an applet with the correct Java platform.

13
Change bonus.html
The only change you need to make to bonus.html is
to have the ACTION parameter in the HTML form
invoke Bonus.jsp instead of BonusServlet.

• ltHTMLgt
• ltBODY BGCOLOR "WHITE"gt
• ltBLOCKQUOTEgt
• ltH3gtBonus Calculationlt/H3gt
• 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
• lt/BLOCKQUOTEgt
• lt/BODYgt
• lt/HTMLgt

14
Create a new Web Component

• Upon the removal of the old WAR file, we have to
  make a new one containing both Bonus.jsp and
  bonus.html.
• WAR display name
• BonusWar
• Component file
• Bonus.jsp

15
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/JSPRoot/bonus.htm
  l
• which is where the Deploy tool put the HTML file.