Understanding JSP Implicit Objects and Directives: A Comprehensive Overview

JSP implicit objects&directive elements Lecture – 20

JSP Journey • directive elements ………………………. • scripting elements • JSP comments………………………………. • declarations ………………………………… • expressions …………………………..…….. • scriptlets……………………………….......... • action elements • special JSP tags ………………………….…. implicit objects

Implicit Objects

Implicit Objects • Objects that can be used in scriplets& expressions without defining them before. • request • response • out • Session • application (used in the ServletContext) • config (used in the ServletConfig, represents configuration options e.g init-parameters) • and more …

Implicit Objectscont. • request:javax.servlet.HttpServletRequest • request object that is the reason for the servlet to run • response:javax.servlet.HttpServletResponse • Response for the request • out:javax.servlet.jsp.JspWriter • Output stream writer

Example of Implicit Objects web.jsp If page = = web index.jsp controller .jsp If page = = java java.jsp

Example Code Use of implicit objects

index.jsp <html> <head> <meta http-equiv="Content-Type" content="text/html"> <title>JSP Page</title> </head> <body> <form name="myForm" action="controller.jsp" method="post"> <h3> <input type="radio" name="page" value="web.jsp" /> Web Site Development </h3> <br/><h3> <input type="radio" name="page" value="java.jsp" /> Beginning Java 2 </h3> <br/> <input type="submit" value="Submit" /> </form> </body></html>

controller.jsp <body> <% //reading parameters data from index.jsp page //by using implicit object names String pageName = request.getParameter("page"); //decide which page is moved by the index.jsp page if (pageName.equals("web.jsp")){ response.sendRedirect("web.jsp"); } else if (pageName.equals("java.jsp")){ response.sendRedirect("java.jsp"); } %> </body>

Web.jsp <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>JSP Page</title> </head> <body> <% out.println("<h3> Welcome to Web.jsp"); %> </body> </html>

Java.jsp <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>JSP Page</title> </head> <body> <% out.println("<h3> Welcome to Java.jsp"); %> </body> </html>

JSP Journey • directive elements ………………………. • scripting elements • JSP comments………………………………. • declarations ………………………………… • expressions …………………………..…….. • scriptlets……………………………….......... • action elements • special JSP tags ………………………….…. implicit objects

JSP Directives

JSP Directives • Used to convey special processing information about the page to JSP container • Enable programmer to: • Specify page settings • Include content from other resources • Specify custom-tag libraries

JSP Directives cont. • Format • <%@ directive {attribute=“val”}* %> • JSP directives • page: <%@page {attribute=“val”}* %> • include: <%@include {attribute=“val”}* %> • taglib: <%@taglib {attribute=“val”}* %>

JSP page Directive

JSP page Directive • Give high level information about servlet that will result from JSP page • Can be used anywhere in the document • Can control • Which classes are imported • What class the servlet extends • How multithreading is handled • If the servlet participates in session • Which page handles unexpected errors

JSP page Directive cont. • Defines attributes of the page • <%@ page {attribute=“val”}* %> • Some Attributes • language = “java” • extends = “package.class” • import = “package.*,package.class,…” • session = “true | false” • errorPage = “relativeURL” • isErrorPage = “true | false”

JSP page Directive cont. • Some example uses are: • To import the package like java.util • <%@ page import = “java.util.*” info = “using util package” %> • To declare this page as an error page • <%@ page isErrorPage = “true” %>

JSP include Directive

JSP include Directive • Lets you include (reuse) navigation bars, tables and other elements in JSP page • You can include files at • Translation Time (by using include directives) • Request Time (by using Action elements)

Including Pages at Translation Timeusing include directive • Format <%@include file=“relativeURL”%> • Purpose • To include a file in JSP document at the time document is translated into a servlet. • May contain JSP code that affect the main page such as response header settings etc.

Example Code use of include directive

header.jsp <%@page contentType="text/html"%> <%@page import="java.util.*" %> <html> <head> <title>JSP Page</title> </head> <body> <marquee> <h3> Enterprise Application Development </h3> <h3> <%= new Date() %> </h3> </marquee> </body> </html>

footer.jsp <%@page contentType="text/html"%> <%@page import="java.util.*" %> <html> <head> <title>JSP Page</title> </head> <body> <marquee> <h3> PUCIT </h3> </marquee> </body> </html>

includeindex.jsp <%@page contentType="text/html"%> <html> <head> <title>JSP Page</title> </head> <body> <%@ include file="header.jsp" %>

includeindex.jsp <table border=1> <tr> <th> </th> <th> Apples <th> Oranges <tr> <th> First Quarter <td> 2307 <td> 4706 <tr> <th> Second Quarter <td> 2982 <td> 4005 <tr> <th> Third Quarter <td> 3052 <td> 3798 <tr> <th> Forth Quarter <td> 3055 <td> 5287 </table> <%@ include file="footer.jsp" %> </body> </html>

XML Syntax for Directives • <jsp:directive.directiveType attribute=“value” /> • For example, the XML equivalent of <%@ page import = “java.util.*” %> Is <jsp:directive.pageimport=“java.util.*” />

JSP Life Cycle Methods

JSP Life Cycle Methods jspInit() Request Response _jspService() jspDestroy()

Understanding JSP Implicit Objects and Directives: A Comprehensive Overview