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Simplifying Web Programming with JSP Scripting Elements

Learn how to separate presentation from processing in web development using Java Server Pages (JSP). Explore JSP scripting elements, page directives, and pre-defined variables for efficient code generation and website development.

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Simplifying Web Programming with JSP Scripting Elements

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  1. CS320 Web and Internet ProgrammingJSP Scripting Elements and Page Directives Chengyu Sun California State University, Los Angeles

  2. Java Server Page (JSP) • Why? • It’s tedious to generate HTML using println() • Separate presentation from processing • How? • Java code embedded in HTML documents

  3. HelloJSP1.jsp <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML> <HEAD><TITLE>Hello JSP 1</TITLE></HEAD> <BODY>A JSP without J or S.</BODY> </HTML>

  4. HelloJSP2.jsp <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML> <HEAD><TITLE>JSP Hello World</TITLE></HEAD> <BODY>Hello World on <%= new java.util.Date() %>. </BODY> </HTML>

  5. How Does JSP Work? • Look under $CATALINA_HOME/work/Catalina/localhost/context_name convert compile execute JSP Servlet ByteCode automatically done by server

  6. 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(...)

  7. JSP Components • HTML template text • Code elements of Java • Directives • Comments • Scripting elements • Beans • Expression language • Custom tag libraries

  8. Directives • Affect the overall structure of the JSP • <%@typeattr=“value” ...%> • Three types of directives • page • include • taglib

  9. Some Page Directives <%@ page import=“java.util.*, java.util.zip.*” %> <%@ page contentType=“text/html” %> <%@ page pageEncoding=“Shift_JIS” %> <%@ page session=“false” %> <%-- default is true --%>

  10. Comments • <%-- Hidden Comments --%> • <!-- Output (HTML) Comments -->

  11. JSP Scripting Elements • JSP Expressions • JSP Scriptlets • JSP Declarations

  12. JSP Expressions • <%= Java expression %> • What’s an expression?? <%= expression %> in JSP out.write( expression ) in _jspService()

  13. Example: Add.jsp • Add two integer parameters and display the sum

  14. 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.

  15. JSP Scriptlets • <% Java code %> • All code goes inside_jspService()

  16. Example: Add.jsp Again • Add the code to validate the parameters

  17. Another Scriptlet Example <% if( Math.random() < 0.5) { %> <H1>Have a <I>nice</I> day!</H1> <% } else { %> <H1>Have a <I>lousy</I> day!</H1> <% } %>

  18. JSP Declarations • <%! class variables or methods %> • All code goes outside_jspService()

  19. Example: RequestCounter.jsp • Initialize a counter as a class variable • Increment the counter each time the JSP is requested

  20. About JSP Scripting Elements • There is a straightforward mapping between JSP with scripting elements and servlet • Mixing presentation and processing • hard to debug • hard to maintain • No clean and easy way to reuse code

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