Introduction to JSP with Forms and JavaBeans

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Introduction to JSPwith Forms and JavaBeans

• Simon M. Lucas
• CC292

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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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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
• See also Date_jsp.java the Servlet this page
  is translated to

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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
• Import some Java packages (comma sep.)
• lt_at_ page importjava.util.Collectiongt

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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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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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HTML Forms

• Allow user to supply input
• Text Fields single line
• Password field single line, blanked-out text
• Text Areas multi-line
• Choice (pop-up menu)
• Radio-button (1 from n)
• Check-box (m from n)
• Browse button
• Submit buttons

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Form Generation

• Need to generate the HTML to send to the client
• The forms should be well presented
• e.g. aligned in a table
• Need to name the input fields
• So that we may extract the data from the
  submitted form
• Next some sample form elements

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Some sample form elements

• linked/FormElements.html

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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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Submission Data Formats

• When a form is generated, it can also specify the
  data format
• By default, this is plain text
• But can also be a MIME format
• MIME allows upload of binary data (via base-64
  encoding)
• Hence allows files of any type to be uploaded to
  a web server

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Form Life-Cycles and Data Models

• Where does a form come from?
• Where are the data-types specified?
• Whats the destination for the form input data?
• How do we best validate it on the server?
• What kind of data models are appropriate?
• Can we separate form content from form
  presentation?

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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 (not covered in this course)
• XForms not covered, but well worth a read if
  youre keen!
• MS InfoPath installed in the Lab can
  auto-generate forms from XML Schemas

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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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Lab Exercises

• Try typing in and running running these JSP
  examples for yourself
• Instructions for Tomcat see Lab pages
• Also study the servlet code produced (in the
  tomcat\work directory