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JavaServer Pages

Posted Date: 25 Mar 2008 Resource Type: Articles/Knowledge Sharing Category: General

Posted By: rajasekhar Member Level: Gold
Rating:

Points: 5

JSP (JavaServer Pages)
Why JSP Technology?

•Servlets are good at running logic
–Not so good at producing large amounts of output
–out.write() is ugly
•JSP pages are great at producing lots of textual output
–Not so good at lots of logic
–<% %> is ugly

How does it Work

•“JSP page”
–Mixture of text, Script and directives
–Text could be text/ html, text/ xml or text/ plain
•“JSP engine”
–‘Compiles’ page to servlet
–Executes servlet’s service() method
•Sends text back to caller
•Page is
–Compiled once
–Executed many times

Anatomy of a JSP

<%@ page language=“java” contentType=“text/html” %>

The following information was saved:
User Name:

Welcome!

JSP Elements
•Directive Elements : –Information about the page
–Remains same between requests
–E.g., scripting language used
•Action Elements : –Take action based on info required at request-time
•Standard
•Custom (Tags and Tag Libraries)
•Scripting Elements
–Add pieces of code to generate output based on conditions

Directives
•Global information used by the “JSP engine”
•Of form <%@ directive attr_ list %>
•Or
–Directive could be
•Page
•Include
•Taglib
–E. g.,
<%@ page info=“ written by DevelopMentor” %>

<%@ include file =“\ somefile. txt” %>
<%@ taglib uri = tags prefix=“ foo” %>
Actions Within a JSP Page
•Specifies an action to be carried out by the “JSP engine”
•Standard or custom
–Standard must be implemented by all engines
–Custom defined in tag libraries
•Standard actions ‘scoped’ by ‘jsp’ namespace
•Have name and attributes

Date:
Month:

Standard JSP Actions :
•jsp:useBean
•jsp:getProperty
•jsp:setProperty
•jsp:include
•jsp:forward
•jsp:param
•jsp:plugin

Scriptlets
•Of form <% /* code goes here*/ %>
–Gets copied into _ jspService method of generated servlet
•Any valid Java code can go here

CODE: OUTPUT
<% int j; %> 0
<% for (j = 0; j < 3; j++) {%> 1
2
<% out. write(""+ j); %>
<% } %>

Declarations (<%! … %>)
•Used to declare class scope variables or methods
<%! int j = 0; %>
•Gets declared at class- level scope in the generated servlet
•
public class SomeJSP extends HttpServlet implements HttpJspPage {
…
int j = 0;
void _jspService(…) {}
}

Declarations (<%! … %>)
•Used to declare class scope variables or methods
<%! int j = 0; %>
•Gets declared at class- level scope in the generated servlet
•
public class SomeJSP extends HttpServlet implements HttpJspPage {
…
int j = 0;
void _jspService(…) {}
}

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