Applet vs' Servlet

1
Applet vs. Servlet

• Use Java Plug-In to deliver applets for intranet
  applications.
• Security restrictions can be managed using policy
  tool to list trusted sites.
• Downloaded classes are usually measured in
  megabytes, OK over high-speed internet
  connections.
• Java Plug-In installs the approriate JDK version
  OK for corporate users.
• Dont use applets for internet applications. Use
  scripting for data validation, animated GIFs for
  animation, use forms and server-side processing
  (whether they are traditional CGI scripts, Java
  servlets, or server side scripting languages) for
  data entry.

2
J2EE Applications Programming

• Application
• Applet
• Remote Method Invocation
• Java Bean
• Enterprise Java Bean
• Servlet
• Java Server Page

3
Thin Client Multitiered Architecture
4
J2EE Platform
5
Bonus Calculation Form
6
Bonus.html

• ltHTMLgt
• ltBODY BGCOLOR "WHITE"gt
• ltBLOCKQUOTEgt
• ltH3gtBonus Calculationlt/H3gt
• ltFORM METHOD"POST" ACTION"servlet/mypackage.Bonu
  sServlet"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/FORMgt
• lt/BLOCKQUOTEgt

7
BonusServlet Output
8
BonusServlet

• Context ctx null
• // Retrieve EJB
• try
• ctx new InitialContext()
• Object homeObject ctx.lookup("GerlachEmp")
  
• EmpHome empHome (EmpHome)
• PortableRemoteObject.narrow(homeObject,EmpHome
  .class)
• Emp emp empHome.findByPrimaryKey(new
  EmpPK(ssn))
• // Output Calculation -- Use EJB
• out.println("ltPgtSalary Amount retrieved "
  emp.getSal() "ltPgt")
• out.println("ltPgtMultiplier " multiplier
  "ltPgt")
• out.println("ltPgtBonus Calculation "
  emp.getSal() multiplier "ltPgt")
• out.println("lt/BODYgtlt/HTMLgt")
• // end of try block
• catch(Throwable ex)
• out.println("ltPgtNo Such EmployeeltPgt")

• public class BonusServlet extends HttpServlet
• public void init(ServletConfig config) throws
  ServletException
• public void doPost (HttpServletRequest request,
  HttpServletResponse response) throws
  ServletException, IOException
• doGet (request, response)
• 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")
• //Retrieve User Input

9
Create and Run Servlet

• File New Html to create html page to launch
  servlet
• File New HTTP Servlet to create servlet class
• Code the servlet to access local EJBs (cannot run
  servlet locally with remote EJBs).
• Link the .html page to the servlet by specifying
  it's path name in the ACTION tag.
• Right click on html page and select run (or
  debug) in browser to execute. JDeveloper will
  start your EJBs automatically -- Do not start
  EJBs yourself.
• Terminate the process before retesting!

10
Get and Post Methods

• doGet technique encodes user input values in the
  URL (CGI script support)
• doPost technique places the user input values
  into the body of the request
• Code doGet and doPost methods in the exact same
  way doGet can call doPost or vice versa.
• The method used (doGet or doPost) is determined
  by the METHOD tag METHOD GET or METHOD POST.

11
Conditional Servlet Invocation

• Provide code in the servlet to create alternative
  HTML pages.
• Code the servlet to select a static html page as
  a response. (Valid for Get requests only)
• RequestDispatcher rd getServletContext().getRequ
  estDispatcher("ssnerror.html")
• rd.forward(request, response)
• This option did not seem to want to work in
  JDeveloper
• Code the servlet to redirect the request and
  response to another servlet or html page.
• response.sendRedirect("/servlet/mypackage.BonusSe
  rvlet2Calc")
• response.sendRedirect("/ssnerror.html")
  response.sendRedirect("http//132.194.120.1967070
  /Servlet_html/ssnerror.html")

12
Multiple Buttons

• Bonus2.Html page specification of buttons
• ltINPUT TYPE"SUBMIT" NAME "SUBMITBUTTON"
  VALUE"Submit"gt
• ltINPUT TYPE"SUBMIT" NAME "CANCELBUTTON"
  VALUE"Cancel"gt
• BonusServlet2 checks button type in doGet
• String cancel request.getParameter("CANCELBUTTON
  ")
• if(cancel!null)
• if (cancel.equals("Cancel"))
• response.sendRedirect("/Cancel.html")
• return
• String submit request.getParameter("SUBMITBUTTON
  ")
• if (submitnull)
• response.sendRedirect("/Cancel.html")
• return

13
Accessing Session Variables

• BonusServlet2doGet supplies Emp object
• EmpHome empHome (EmpHome)ctx.lookup("GerlachEmp"
  )
• Emp emp empHome.findByPrimaryKey(new
  EmpPK(ssn))
• HttpSession session request.getSession(true)
• session.setAttribute("employee", emp)
• session.setAttribute("multiplier", new
  Integer(multiplier))
• response.sendRedirect("/servlet/mypackage.BonusSer
  vlet2Calc")
• BonusServlet2CalcdoGet uses Emp object
• HttpSession session request.getSession(false)
  
• Emp emp Integer I int multiplier
• try
• if (session ! null)
• emp (Emp) session.getValue("employee")
• I (Integer) session.getValue("multiplier")
  
• multiplier I.intValue()
• out.println("ltPgtSoc Sec " emp.getEmpno()
  "ltPgt")
• out.println("ltPgtSalary Amount retrieved "
  emp.getSal() "ltPgt")
• out.println("ltPgtMultiplier " multiplier
  "ltPgt")
• out.println("ltPgtBonus Calculation "
  emp.getSal() multiplier "ltPgt")

14
GUI Components for Forms

• Handout

15
Application Design

• Initial user screen is an html page.
• The initial user screen calls the first servlet
  when user hits the submit button.
• The reply html page produced by the first servlet
  will specify a second servlet in the METHOD tag.
  
• When the user depresses the submit button of the
  reply html page, the second servlet is invoked.
  Servlet two creates yet another reply page that
  is associated with a third servlet. And so the
  processing goes.