Java Server Pages (JSP)

1
Java Server Pages (JSP)
2
A Java Servlets Example

• A simple "HelloWorld" servlet, that also prints
  the current date.
• import java.io.
• import javax.servlet.
• import javax.servlet.http.
• public class HelloWorld extends HttpServlet
• public void doGet(HttpServletRequest req,
  HttpServletResponse res) throws ServletException,
  IOException
• res.setContentType("text/html")
• PrintWriter out res.getWriter()
• out.println("ltHTMLgt")
• out.println("ltHEADgtltTITLEgtHello
  Worldlt/TITLEgtlt/HEADgt")
• out.println("ltBODYgt")
• out.println("ltH1gtHello Worldlt/H1gt")
• out.println("Today is " (new
  java.util.Date().toString()) )
• out.println("lt/BODYgtlt/HTMLgt")
• // doGet
• // HelloWorld
• In order to run it, do the following
• Place it in a file, HelloWorld.java
• Compile it.

3
A JSP Example

• The previous page can be written using JSP as
  shown below
• ltHTMLgt
• ltHEADgt
• ltTITLEgtHello Worldlt/TITLEgt
• lt/HEADgt
• ltBODYgt
• ltH1gtHello Worldlt/H1gt
• Today is lt new java.util.Date().toString()
  gt
• lt/BODYgt
• lt/HTMLgt
• In order to run it, do the following
• Place it in a file, HelloWorld.jsp in the same
  directory as your .html files
• Run it by pointing browser to http//server.addre
  ss/youraccount/HelloWorld.jsp

4
Elements of JSP

• Whenever a .jsp is requested for the first time,
  the server does the following
• 1. Translates the .jsp page into a servlet2.
  Compiles the servlet into a class file3.
  Executes the servlet (response is sent to the
  client)
• Subsequent requests (as long as the .jsp page is
  unchanged) use the same loaded class file.
• Anatomy of a JSP Page
• A JSP page is a mixture of standard HTML tags,
  web page content, and some dynamic content that
  is specified using JSP constructs. Everything
  except the JSP constructs is called Template
  Text.

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JSP Constructs JSP Comments

• JSP Comments Different from HTML comments
• lt!-- an HTML comment --gt
• lt-- a JSP comment --gt
• JSP comments are used for documenting JSP code
  and are not visible client-side (using browser's
  View Source option) where as HTML comments are
  visible.

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JSP Constructs JAVA Expressions

• Format lt some_java_expression gt
• Examplelt new java.util.Date().toString() gt
• Output of the expression is placed in the HTML
  template at the same location.

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JSP Constructs Variables in JAVA Expressions

• There are some pre-defined Java variables/objects
  available for use in expressions (provide access
  to important servlet functionality)
• requestThis is the same object as
  HttpServletRequest parameter in th get/post
  methods. Same methods (like, getParameter,
  getAttribute, etc) can be applied to it.
• outThe servlet printwriter.
• sessionSame as servlet session object.
• Example
• ltHTMLgt
• ltHEADgt
• ltTITLEgtJSP Expressions Predefined
  Objectslt/TITLEgt
• lt/HEADgt
• ltBODYgt
• ltH1gtUsing Predefined Objectslt/H1gt
• ltULgt
• ltLIgt Your Hostname lt request.getRemoteHos
  t() gt
• ltLIgt Your Session ID lt session.getId()
  gt
• ltLIgt The value of INFO parameter lt
  request.getParameter("INFO") gt
• lt/BODYgt
• lt/HTMLgt

8
JSP Constructs Scriptlets

• Scriptlets are arbitrary pieces of Java code
  inserted in the page using the format lt
  some_java_code gt

Example 2 ltHTMLgt ltHEADgt ltTITLEgtJSP
Scriptlets 2lt/TITLEgt lt/HEADgt lt String
bgColor request.getParameter("COLOR") gt
lt if (bgColor null) gt
ltBODY BGCOLOR"FFFFFF" gt lt else gt
ltBODY BGCOLOR"lt bgColor gt" gt lt
gt ltH1gtExample Scriptlet
Conditionally sets background colorlt/H1gt lt
if (bgColor null) gt You did not
supply a color, I used white. lt else
gt Here is the color you requested.
lt gt lt/BODYgt lt/HTML
Example 1 ltHTMLgt ltHEADgt ltTITLEgtJSP
Scriptletslt/TITLEgt lt/HEADgt lt
String bgColor request.getParameter("COLOR")
if (bgColor null)
bgColor "WHITE" gt ltBODY
BGCOLOR"lt bgColor gt" gt ltH1gtExample
Scriptlet Sets background colorlt/H1gt
lt/BODYgt lt/HTMLgt
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JSP Constructs Scriptlets, contd.

• Using Arrays One can easily use scriptlets to
  loop over arrays. In this example, the user is
  presented with choice boxes. When s/he presses
  the submit button, the choices are displayed.
• Example
• ltHTMLgt
• ltBODY BGCOLOR"WHITE"gt
• ltFORM ACTION"choices.jsp"gt
• ltINPUT type"checkbox" name"music"
  value"Classical"gt ClassicalltBRgt
• ltINPUT type"checkbox" name"music"
  value"Rock"gt RockltBRgt
• ltINPUT type"checkbox" name"music"
  value"Jazz"gt JazzltBRgt
• ltINPUT type"checkbox" name"music"
  value"Blues"gt BluesltBRgt
• ltINPUT type"checkbox" name"music"
  value"DC-GoGo"gt DC GoGoltBRgt
• ltINPUT type"submit" value"Submit"gt
• lt/FORMgt
• lt
• String selected request.getParameterVal
  ues("music")
• if (selected ! null selected.length !
  0)
• gt
• You like the following kinds of music
• ltULgt
• lt

10
JSP Constructs Declarations

• You can define variables and/or methods lt! some
  JAVA declarations gt
• Example
• ltHTMLgt
• ltBODYgt
• lt!
• private int hitCount 0
• String randomColor()
• java.util.Random random new java.util.Random()
  
• int R (int) (random.nextFloat() 255)
• int G (int) (random.nextFloat() 255)
• int B (int) (random.nextFloat() 255)
• return "" Integer.toString(R, 16)
  Integer.toString(G, 16) Integer.toString(B,
  16)
• gt
• ltFONT COLOR"lt randomColor() gt" gt This page
  has been accessed lt hitCount gt times.
  lt/FONTgt
• lt/BODYgt
• lt/HTMLgt

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JSP Constructs Summary

• Expressions
• Scriptlets
• Declarations
• Availability of pre-defined objects

12
JSP Directives

• Format
• lt_at_ directive attribute"value" gt
• lt_at_ directive attr1"value" attr2"value" ...
  attrN"value" gt
• Directives are used to specify the structure of
  the resulting servlet. There are three
  directives page, include, and taglib

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JSP Page Directive

• There are 11 specifiable attributes for this
  directive import, contentType, isThreadSafe,
  session, buffer, autoflush, extends, info,
  errorPage, and language
• Example
• lt_at_ page language"java" contentType"text/html"
  gt
• lt_at_ page contentType"application/vnd.ms-excel"
  gt
• lt_at_ page import"java.util." gt
• lt_at_ page import"java.util.,java.io." gt
• Directives can be placed anywhere in the
  document, but are often placed at the very top.
• lt_at_ page language"java" contentType"text/html
  import"java.util." gt
• ltHTMLgt
• ltHEADgt
• ltTITLEgtHello Worldlt/TITLEgt
• lt/HEADgt
• ltBODYgt
• ltH1gtHello Worldlt/H1gt
• Today is lt new Date().toString() gt
• lt/BODYgt
• lt/HTMLgt

14
JSP Other Directives

• The include Directive
• Is used to include a file in the main document.
• There are two versions of this. The first one,
  shown below, includes the file at translation
  time.
• lt_at_ include file"relative URL of file" gt
• The second version, includes the file at request
  time.
• ltjspinclude page"ralative URL of file"
  flushtrue /gt
• The taglib directive
• This is used to define custom markup tags. Refer
  to JSP documentation for details on this.