CS320 Web and Internet Programming JSP Scripting Elements and Page Directives

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CS320 Web and Internet ProgrammingJSP Scripting
Elements and Page Directives

• Chengyu Sun
• California State University, Los Angeles

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Java Server Page (JSP)

• Why?
• Its tedious to generate HTML using println()
• Separate presentation from processing
• How?
• Java code embedded in HTML documents

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HelloJSP1.jsp
lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
Transitional//EN"gt ltHTMLgt ltHEADgtltTITLEgtHello JSP
1lt/TITLEgtlt/HEADgt ltBODYgtA JSP without J or
S.lt/BODYgt lt/HTMLgt
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HelloJSP2.jsp
lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
Transitional//EN"gt ltHTMLgt ltHEADgtltTITLEgtJSP Hello
Worldlt/TITLEgtlt/HEADgt ltBODYgtHello World on lt new
java.util.Date() gt. lt/BODYgt lt/HTMLgt
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How Does JSP Work?
convert
compile
execute
JSP
Servlet
ByteCode
automatically done by server

• Look under CATALINA_HOME/work/Catalina/localhost/
  context_name

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Some Simple Observations about the JSP/Servlets

• In package org.apache.jsp
• _jspService() handles everything
• replaces service() in HttpServlet
• What happened to doGet(), doPost(), ...??
• HTML text ? out.write(...)

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Pre-defined Variables

• request, response, out
• session, application
• config, pageContext
• page

The same request, response, session etc. that are
used in servlets see the Servlet API
documentation for what you can do with them.
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JSP Components

• HTML template text
• Code elements of Java
• Scripting elements
• Directives
• Beans
• Expression language
• Custom tag libraries

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Comments

• lt-- Hidden Comments --gt
• lt!-- Output (HTML) Comments --gt

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JSP Expressions

• lt Java expression gt
• Whats an expression??

lt expression gt in JSP
out.write( expression ) in _jspService()
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Example Add.jsp

• Add two integer parameters and display the sum

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JSP Scriptlets

• lt Java code gt
• All code goes inside _jspService()

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Example Add.jsp Again

• Add the code to validate the parameters

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Another Scriptlet Example
lt if( Math.random() lt 0.5) gt ltH1gtHave a
ltIgtnicelt/Igt day!lt/H1gt lt else gt ltH1gtHave a
ltIgtlousylt/Igt day!lt/H1gt lt gt
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JSP Declarations

• lt! class variables or methods gt
• All code goes outside _jspService()

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Example RequestCounter.jsp

• Initialize a counter as a class variable
• Increment the counter each time the JSP is
  requested

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JSP Scripting Elements

• JSP Expressions
• JSP Scriptlets
• JSP Declarations

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Directives

• Affect the overall structure of the JSP
• lt_at_ type attrvalue ... gt
• Three type of directives
• page
• include
• taglib

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Some Page Directives
lt_at_ page importjava.util., java.util.zip.
gt lt_at_ page contentTypetext/html gt lt_at_ page
pageEncodingShift_JIS gt lt_at_ page
sessionfalse gt lt-- default is true --gt

• isELIgnored, errorPage, isErrorPage