JSP Architecture JSP is a simple text file consisting of HTML or XML content along with JSP...

JSP Architecture

JSP is a simple text file consisting of HTML or XML content along with JSP elements

JSP packages define the interface for the compiled JSP page

JSPPage HttpJspPage

Three main methods jspInit() jspDestroy() _jspService(HttpServletRequest request,HttpServletResponse response)

Elements of a JavaServer Page

JSP Elements

“Template Text” – HTML

When request is processedtemplate text & dynamic content mergedresult sent as response to browser

JSP ElementsDirectiveActionScripting

Elements of a JavaServer Page

Directives provide global information to the page

Action perform action based on up-to-date information

Scripting Declarative

for page-wide variable and method declaration Scriptlets

the Java code embedded in the page Expressions

Format the expression as a string for inclusion in the output of the page.

JSP Syntax HTML Comment

Comment can be viewed in the HTML source file



Example:



View source:

JSP Syntax Hidden Comment

Everything between the <%-- and --%> is ignored by the JSP containerComment cannot be viewed in the HTML sourcefile

<% -- expression -- %>

Example:

<html><body><h2>A Test of Comments</h2><%--This comment will be invisible in page source --%></body></html>

JSP Directives

A JSP directive is a statement that gives the JSP engine information for the page.

Used to provide information about the general set-up of the page. e.g. inclusion of header files, name of page to report errors, whether session tracking is required etc

Syntax<%@ directive {attribute= “value” } %>

For Example:scripting language usedsession tracking requiredname of page for error reporting

Types of Directive Elements

<%@ page ... %> Define page-dependent attributes, such as scripting language, error page & buffering requires

<%@ include ... %> Include a file during the translation phase.

<%@ taglib ... %> Declares a tag library, containing custom actions, used in the page

Each directive has a set of associated attributes (similar to some tags in HTML)Full list of attributes available at: http://java.sun.com/products/jsp/syntax/1.1/syntaxref11.html

JSP Syntax Include Directive

Includes a static file<%@ include file=“relativeURL” %>

Example:main.jsp: <html><body>

Current date and time is:<%@include file=“date.jsp” %></body></html>

date.jsp: <%@page import =“java.util.*” %><% =(new java.util.Date()).toLocaleString()

%>

Output : Current date and time is:Mar 5, 2000 4:56:50

Attribute for the page directive and possible values

language-- The language attribute defines the scripting language to be used in the page. The value "java" is the only value currently defined and is the default.

extends-- The extends attribute defines the (fully-qualified) class name of the superclass of the servlet class that is generated from this JSP

page.

import-- The import attribute defines the set of classes and packages that must be imported in the servlet class definition.


session-- The session attribute defines whether the JSP page is participating in an HTTP session. The value is either true (the default) or false.

Buffer-- The buffer attribute defines the size of the buffer used in the output stream (a JspWriter object). The value is either none or

Nkb.

autoFlush-- The autoFlush attribute defines whether the buffer output should be flushed automatically when the buffer is filled or whether an exception is thrown. The value is either true (automatically flush) or false (throw an exception). The default is true.


isThreadSafe-- The isThreadSafe attribute defines whether the JSP servlet implements the SingleThreadModel interface. The value is either true or false. The default is true.

Info-- The info attribute defines an informational string about the JSP page.

errorPage-- The errorPage attribute indicates another JSP page that will handle all runtime exceptions thrown by this JSP page. The value is a URL that is either relative to the current Web hierarchy or relative to the context root. For example, errorPage="error.jsp" (this is relative to the current hierarchy) orerrorPage="/error/formErrors.jsp" (this is relative to the Web application's context root).


isErrorPage-- The isErrorPage attribute defines that the JSP page has been designed to be the target of another JSP page's errorPage attribute. The value is either true or false (default). All JSP pages that "are an error page" automatically have access to the exception implicit variable.

JSP action elements

Action elements are an important syntax element in JSPThey are represented by tags (as is HTML)They assist JSP developers to develop in tags rather than scriplet programmingInstead of <%, they just use the < character (like HTML)

For example: <prefix:action_name>

body </prefix:action_name >

JSP action elements

Full syntax of JSP Action Elements is: <prefix:action_name attr1 = “value” attr2 =

“value2”> action_body

</prefix:action_name>If the element doesn’t have a body, can lose the end tag and use shorthand syntax of:

<prefix:action_name attr1 = “value” attr2 = “value2” />

JSP action elements

There are two types of JSP action elements:

1. JSP Pre – defined tags, also called Standarded Action Elements.

2. External tag library: Custom or JSTL(Java Standard tag library)

JSP standard action elements

jsp:useBeanjsp:setPropertyjsp:getPropertyjsp:paramjsp:includejsp:forwardjsp:pluginjsp:paramsjsp:fallback


Standard Action Example: <JSP: include> tagExample:

<HTML> <BODY>

Going to include hellouser.jsp...<BR>

<jsp:include page="hellouser.jsp"/>

</BODY>

</HTML>

Executes the included JSP page and adds its output into the this page


What’s difference from using the “include” derective? The include directive includes the contents of another file at compilation time. Good for including common static code e.g. header file, footer file. Good on performance included only once.

But, what if including dynamic common code (e.g. a navigation bar where links are read from the dB?).. need to re-run the file each time a request is made JSP: include


Standard Action Example: <JSP: forward> tagExample:

<HTML> <BODY>

Error occurred…please wait<BR>

<jsp:forward page=“errorhandle.jsp"/>

</BODY>

</HTML>

Stops processing of one page and starts processing the page specified by the page attribute

JSP Declaration

The definition of class-level variables and methods

Syntax<%! Declaration %>

Example

<%! String var1 = “hi”;int count = 0;

private void incrementCount() {count++;}

%>

JSP Scriptlets

Scriptlets are defined as any block of valid Java code that resides between <% and %> tags

This code will placed in the generated servlet _jspService() method.

Example

<%String var1 = request.getParameter(“lname”);out.println(var1);

%>

JSP Expressions

A JSP expression is a nice tool for embedding values within your HTML code.

Syntax<%= expression %>

Example

<% for (int i = 0; i < 10; i++) { %><BR>Counter value is <%= i %><% } %>

Scripting: Implicit JSP Objects

Request -- The HttpServletRequest object associated with the request

Response-- The HttpServletResponse object associated with the response that is sent back to the browser

pageContext-- This object encapsulates the environment of a single request for this JSP page

Session-- The HttpSession object associated with the session for the given user of the request. This variable is only meaningful if the JSP page is participating in an HTTP session


Application -- The ServletContext object for the Web application

Out-- The JspWriter object associated with the output stream of theresponse

Config-- The ServletConfig object associated with the servlet for this JSP page

Exception-- The Throwable object that was thrown by some other JSP page. This variable is only available in a "JSP error page."


Example<%@ page errorPage="errorpage.jsp"%><HTML><HEAD><TITLE>Use Out</TITLE></HEAD><BODY>

<%//print a simple message using the implicit out

object out.println( "<center><b>Hello!</b></center>" );

%>

</BODY></HTML>

Use of Implicit Objects…

The following information was part of this request

<li> Request method <%= request.getMethod() %>

<li> Request URI <%= request.getRequestURI() %>

<li> Request Protocal <%= request.getProtocol() %>

<li> Server Name <%= request.getServerName() %>

<li> Server Port <%= request.getServerPort() %>

<li> Remote Address <%= request.getRemoteAddr() %>

<li> Remote Host <%= request.getRemoteHost() %>

Use of Implicit Objects…

Example<%@ page errorPage="errorpage.jsp"%><HTML><HEAD><TITLE>Use Request</TITLE></HEAD><BODY>

<%//print a simple message using the implicit out

object out.println( "<b>Hello!</b>" + request.getParameter("user") + "</b>" );

%>

</BODY></HTML>

JSP Architecture JSP is a simple text file consisting of HTML or XML content along with JSP...

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