Introduction to JSP with Forms and JavaBeans

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Introduction to JSPwith Forms and JavaBeans
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Overview

• Embeds Java code
• In HTML tags
• When used well
• Simple way to generate dynamic web-pages
• When misused (complex embedded Java)
• Terribly messy (and may violate OaOO)
• Keep the embedded Java simple
• Use external helper classes (Beans?)

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How does JSP work?
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Life Cycle

• A JSP page is translated into a Java Servlet
• And then compiled
• On Tomcat, the compilation happens the first time
  a page is requested
• First request can be very slow!
• Afterwards, just as fast as a Servlet (because it
  is then a servlet)

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Hello World

• lthtmlgt
• ltheadgt lttitlegt Hello JSP lt/titlegt lt/headgt
• ltbodygt
• ltpgt Hello World
• lt new java.util.Date() gt
• lt/pgt
• lt/bodygt
• lt/htmlgt

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Date_jsp.java (extract)

• This extract shows the part that produces the
  output compare it with the JSP
• out pageContext.getOut()
• _jspx_out out
• out.write("lthtmlgt\r\n")
• out.write("ltheadgt ")
• out.write("lttitlegt Hello JSP ")
• out.write("lt/titlegt ")
• out.write("lt/headgt\r\n")
• out.write("ltbodygt \r\n")
• out.write("ltpgt Hello World\r\n ")
• out.print( new java.util.Date() )
• out.write("\r\n")
• out.write("lt/pgt\r\n")
• out.write("lt/bodygt\r\n")
• out.write("lt/htmlgt\r\n")

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Produced
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Basic Constructs

• So far weve seen literals
• E.g. lthtmlgt
• Copied straight to output (to browser)
• And expressions
• E.g. lt new java.util.Date() gt
• Return a value included in the output
• Also have
• Directives, Declarations and Scriptlets

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Directives

• Instructions to the compiler
• Examples
• Include another page (compile-time)
• lt_at_ include file"header.jsp" gt
• ltjspinclude page"page.jsp" flush"true" /gt
• What is the difference ???
• Import some Java packages (comma sep.)
• lt_at_ page importjava.util.Collectiongt

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JSP Tags

• These are tags that start with the word jsp as in
  the previous example
• These are mainly for handling form beans as will
  be shown later apart from 3 tags.
• ltjspforward, to forward user to another page
• ltjspforward page"/servlet/login" /gt
• ltjspplugin, to import plugin as a java applet in
  the client browser.
• ltjspplugin typeapplet code"Molecule.class"
  codebase"/html"gt
• ltjspinclude, to include the result of a jsp page

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Declarations

• Used to declare variables and methods
• Go in the declaration section of the Servlet
• Can then be used later in the JSP page
• Note the syntax
• Examples
• lt! int count 0 gt
• lt! double sqr(double x) return x x
  gt

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Scriptlets

• These are sections of Java code embedded in the
  page
• Unlike expressions, they do not return a value
• But may write directly to the page
• Get the writer response.getWriter()
• They go in the service method of the servlet
• Get executed each time a page is requested

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Illustrative Example

• Demonstrates much of the above
• lt! int n 0 gt
• Page accessed lt n gt times
• lt if ( (n 10) 0 )
• n 0
• gt

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What happens on next refresh?
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JSP objects

• Application
• Config
• Out
• Request
• Response
• Session

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Request and Response

• Each JSP page has access to two special objects
• The Request object carries information passed by
  the HTTP request (e.g. made by the browser)
• This includes any submitted form data
• The Response object is used to pass information
  back to the Client (browser)
• E.g. response.getWriter() provides an output
  stream for direct writing to the client

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Form Handling with JSP

• JSP makes form handling easy
• Can use request.getParameter() to get submitted
  values
• Or can define a JavaBean to grab the values
  semi-automatically.
• Well see this in action later with a simple
  example

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Processing form input

• Global object request, session
• lt session.putValue(username,
  request.getParameter(UserName)) gt
• lthtmlgtltbodygt
• Thanks for giving us your name, lt
  session.getValue(username) gt
• lt/bodygtlt/htmlgt

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Form Processing

• The form can specify whether data is supplied via
  a GET or POST request
• POST is the usual way
• Therefore, a servlet should implement the
  doPost() method to process a form
• JSP hides these GET/POST details (see
  request.getParameter and ltjspsetPropertygt)

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Form Processing Architectures

• Helper classes for servlets
• To generate forms ( other HTML)
• Process the form input
• JSP JavaBeans (more later)
• JSP Tag Library (will be covered later)

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JavaBeans

• Come in two types
• Simple (this course)
• Enterprise (EJB more complex, not covered)
• Simple JavaBeans
• Data bound classes
• Define properties (fields)
• Define get/set methods
• See following example

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Hotel Booking Form
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HTML (body) for Booking Form

• ltbodygt
• lth3 align"center"gtWelcome to the Hotel
  Californialt/h3gt
• ltform method"POST" action"BookHotel.jsp"gt
• ltpgtName ltinput type"text" name"name"
  size"20"gtlt/pgt
• ltpgtHow many nights
• ltselect size"1" name"nNights"gt
• ltoption selected""gt1lt/optiongt
• ltoptiongt2lt/optiongt
• ltoptiongt3lt/optiongt
• lt/selectgtlt/pgt
• ltpgt
• ltinput type"submit" value"Submit" name"B1"gt
• lt/pgt
• lt/formgt
• lt/bodygt

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Accessing Submitted Values(manual version)

• lthtmlgt
• ltheadgtlttitlegtBean testlt/titlegtlt/headgt
• ltbodygt
• lth2gt
• ltrequest.getParameter("name") gt
• to stay for
• lt request.getParameter("nNights") gt nights.
• lt/h2gt
• lt/bodygt
• lt/htmlgt

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JavaBean Version (Auto)

• ltjspuseBean id'roomBooking'
• scope'page'
• class'beans.HotelBean'
• /gt
• ltjspsetProperty name'roomBooking' property''
  /gt
• lthtmlgt
• ltheadgtlttitlegtBean testlt/titlegtlt/headgt
• ltbodygt
• lth2gt ltroomBooking.getName()gt
• to stay for
• lt roomBooking.getnNights() gt nights.
  lt/h2gt
• lt/bodygt
• lt/htmlgt

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Java Code for Bean Version

• package beans
• public class HotelBean
• String name
• int nNights
• public String getName()
• return name
• public void setName(String name)
• this.name name
• public int getnNights()
• return nNights
• public void setnNights(int nNights)
• this.nNights nNights

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Resulting Page
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Bean Scope

• Note the setting scope'page'
• Scope has four possible settings
• Page
• Bean exists for execution of that page only
• Request
• Like page, but survives any forward or include
  requests

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Bean Scope (cont.)

• Session
• The Bean exists for multiple requests within the
  web application, from a particular web browser
  instance
• Used for shopping baskets etc.
• Application
• The Bean exists for all requests from all users,
  for all pages that use it.
• Survives until the Web Application Server is
  restarted
• Can be used for a database connection (or
  connection pool)

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Beans v. Manual

• For this example, consider the differences
• JavaBean JSP page more complex
• JavaBean also required an external class
  definition
• Discussion question
• When would JavaBean solutions be better than
  manual versions?
• Answer

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Functions

• lt_at_ page import"java.util." gt
• ltHTMLgt
• ltBODYgt
• lt!    
• Date theDate new Date()    
• Date getDate()            
• return theDate    
• gt
• Hello!  The time is now lt getDate() gt
• lt/BODYgt
• lt/HTMLgt

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Functions

• The JSP can get really intractable with lots of
  scriplets
• A direct example of using scriplet is a for loop
  to display records from a database in a table
  format.
• Put the code for the view in a function and call
  it as much as you need

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Function Loop example

• lt
• public void printRecord(int Number)
• out.print(ltTRgt)
• out.print(ltTDgtNumberlt/TDgt)
• out.print(ltTDgt Numberlt/TDgt)
• out.print(lt/TRgt)
• gt
• ltTABLE BORDER2gt
• lt
• for ( int i 0 i lt n i )
• printRecord(i1)
• gt
• lt/TABLEgt

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Functions

• This doesnt look anymore like an HTML code.
• What is the point of JSP then, is it to get messy
  code!!
• So, sun devised a remedy for that and the final
  result looked really good, but not the
  development
• The solution is called JSP Standard Tag Library
  or JSTL.
• The last example will be written in one tag as
• ltmylib for start1 end10/gt

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JSTL

• Next Lecture