Session12-JSP(1)

8/3/2019 Session12-JSP(1)

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JAD Session 12 JSP 1/26

Session 12

JavaServer Pages (JSP)
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Objectives

JavaServer Pages (JSP)What JSP Technology is and how you can use it. JSP Page

Translation Time

How JSP Works?

JSP Elements

JSP Predefined Variable Implicit Objects

JSP Lifecycle

JSP Directives (chapter 6)The page DirectiveThe include DirectiveThe taglib Directive


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JavaServer Pages (JSP)

What JSP Technology is and how you can use it. JavaServer Pages (JSP) technology provides a simplified,

fast way to create web pages that display dynamically-generated content.

The JSP 1.2 specification is an important part of the Java 2Platform, Enterprise Edition. Using JSP and EnterpriseJavaBeans technologies together is a great way toimplement distributed enterprise applications with web-based front ends.

The first place to check for information on JSP technologyis http://java.sun.com/products/jsp

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JSP Page

A JSP page is a page created by the web developer thatincludes JSP technology-specific tags, declarations, andpossibly scriptlets, in combination with other static HTML orXML tags.

A JSP page has the extension .jsp; this signals to the webserver that the JSP engine will process elements on this page.

Pages built using JSP technology are typically implemented

using a translation phase that is performed once, the firsttime the page is called. The page is compiled into a JavaServlet class and remains in server memory, so subsequentcalls to the page have very fast response times.
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Translation Time

A JSP application is usually a collection of JSP files,HTML files, graphics and other resources.

A JSP page is compiled when your user loads it into a

Web browser1. When the user loads the page for the first time, the files that

make up the application are all translated together, withoutany dynamic data, into one Java source file (a .java file)

2. The .java file is compiled to a .class file. In mostimplementations, the .java file is a Java servlet that complieswith the Java Servlet API.


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Simple JSP Page

First JSP Page


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How JSP Works?

User Request JSP File RequestedUser Request JSP File Requested

ServerServer

File

Changed

File

ChangedCreate Source from JSPCreate Source from JSP

CompileCompile Execute ServletExecute Servlet


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JSP Elements

Declarations

Expressions

Scriplets


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HTML Comment

Generates a comment that is sent to the client.

Syntax

Example:


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Declaration

Declares a variable or method valid in the scripting language used in theJSP page.

Syntax

Examples

You can declare any number of variables or methods within onedeclaration

element, as long as you end each declaration with a semicolon.

The declaration must be valid in the Java programming language.


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Declaration Demo

Demo\JSP1\dec.jsp


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Expression

Contains an expression valid in the scripting language used in the JSP page. Syntax

Description:An expression element contains a scripting language expression that is evaluated,

converted to a String, and inserted where the expression appears in the JSP file. Because the value of an expression is converted to a String, you can use an expressionwithin a line of text, whether or not it is tagged with HTML, in a JSPfile. Expressions areevaluated from left to right.


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Expression Demo

Demo\JSP1\exp.jsp


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Scriptlet

Contains a code fragment valid in the page scripting language.

Syntax

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


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Scriplet Demo

Demo\JSP1\scriptlet.jsp


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JSP Predefined Variable Implicit

Objects request Object of HttpServletRequest (request parameters, HTTP headers, cookies

response Object of HttpServletResponse

out - Object of PrintWriter buffered version JspWriter

session - Object of HttpSession associated with the request

application - Object of ServletContext shared by all servlets in the engine

config - Object of ServletConfig

pageContext - Object of PageContext in JSP for a single point of access

page variable synonym for this object


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JSP Lifecycle

jspInit()jspInit()

jspDestroy()jspDestroy()

jspService()jspService()

Servlet from JSP

Init Event

RequestResponse

Destroy Event


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JSP Directives

Directives, whichlike scripting elementsarepieces of JSP tag-like syntax. Like an XML or HTML

tag, directives have attributes that dictate their

meaning and effect. In almost all cases, the effectsproduced by directives cant be replicated using

expressions, scriptlets, or declarations.

Well consider the three directives:

page,

include,

and taglib.


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The page Directive

You can include a page directive anywhere in

your JSP page source: beginning, middle, or

end.

An example of how one looks:


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The page Directive-import attribute

Import attributeUse the import attribute to create import statements in

the generated servlet source produced by the JSPcontainers translation phase.

Example:

JSP Container will import 04 packages at translationtime:javax.servlet

javax.servlet.http

javax.servlet.jspjava.lang


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The page Directive - contentType

attribute The value of the contentType attribute is a String that specifiesthe MIME type of the response to be sent back.

-1) {os.write(info);

}os.flush();%>


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Other attributes of thepage directive


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The include Directive

A JSP source file and the pages it includes throughthe include directive are collectively referred to as a

translation unit.

The file type you include doesnt have to be JSP pagesource, nor does it have to have a .jsp extension.

Once included, the file contents must make sense to

the JSP translation process, but this gives scope to

include entire HTML or XML documents, ordocument fragments.


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The taglib Directive

The taglib directive makes custom actions

available in the JSP page by referencing a tag

library (will study in the next session).


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Summary JavaServer Pages (JSP)

What JSP Technology is and how you can use it.

JSP Page

Translation Time

How JSP Works?

JSP Elements

JSP Predefined Variable Implicit Objects

JSP Lifecycle

JSP Directives (chapter 6)

The page Directive


The taglib Directive

Session12-JSP(1)

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