DT228/3 Web Development

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DT228/3 Web Development
JSP Actions elements and JSTL
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Introduction

• Previously, identified that JSP provides a
  variety of techniques to enable dynamic
  processing

• Directive elements

• Scripting elements

• Action elements and JSTL

• Java Beans

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JSP Action elements

• Action elements are an important syntax element
  in JSP
• They are represented by tags (as is HTML)
• They assist JSP developers to develop in tags
  rather thanscriplet programming
• Instead of lt, they just use the lt character
  (like HTML)

ltprefixaction_namegt body
lt/prefixaction_name gt
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JSP Action elements

• JSP tags have a start tag, a tag body and an
  end tag.
• The start and end tag have the same name enclosed
  in lt and gt
• The tag names have an embedded colon character
  in them, the part before the colon (prefix)
  describes the type of the tag

ltprefixaction_namegt body lt/prefixaction_na
megt

• Part after the is the Action Name

• Note Syntax of Action Elementags is based on XML

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JSP Action elements

• Tags have associated attributes (like HTML e.g.
  ltimg src ..)
• Full syntax of JSP Action Elements is
• ltprefixaction_name attr1 value attr2
  value2 action_bodylt/prefixaction_namegt
  If the element doesnt have a body, can lose the
  end tag and use shorthand syntax
  ofltprefixaction_name attr1 value attr2
  value2 /gt

For example
ltjspinclude page"scripts/login.jsp" /gt
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JSP Action elements
Two types
1.
2.
JSP Pre-defined tags
External tag library (e.g. JSTL)
Tags prefix is ltjsp .gt
Tags prefix is whatever developer chooses or
library recommends
Custom and JSTL
(Also called Standard Action Elements)
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JSP Action elements
JSP pre-defined tags (standard actions elements)
External Tag library -------? Custom
-------? Java Standard tag library
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JSP Action elements JSP Predefined Tags

• Also called JSP Standard Action Elements
• List of these elements are ltjspforwardgt
• ltjspincludegt
• ltjspparamgt
• ltjspplugingt
• ltjspuseBeangt
• ltjspgetPropertygt
• ltjspsetPropertygt
• See http//java.sun.com/products/jsp/syntax/1.1/sy
  ntaxref11.html for detailed attributes and values

Used for Java Beans
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JSP Predefined Tag Example ltjspincludegt

• Standard Action Example ltJSP includegt tag
• Example
• ltHTMLgt ltBODYgt
• Going to include hello.jsp...ltBRgt
• ltjspinclude page"hello.jsp"/gt
• lt/BODYgt
• lt/HTMLgt
• Executes the included JSP page and adds its
  output into the this page

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JSP Predefined Tag Example ltjspincludegt

• Whats Difference from Using the include
  directive? e.g. lt_at_ include file hello.jsp
  gt
• 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
• JSP include incorporates the output of the
  included JSP file at run time

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JSP Predefined Tag Example ltjspforwardgt

• Standard Action Example ltJSP forwardgt tag
• Stops processing of one page and starts
  processing the page specified by the page
  attribute
• Example
• ltHTMLgt ltBODYgt
• Error occurredplease waitltBRgt
• ltjspforward pageerrorpage.jsp"/gt
• lt/BODYgt
• lt/HTMLgt

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JSP Predefined Tag Example ltjspparamgt

• Standard Action Example ltJSP paramgt tag
• Can be used to pass parameters when using
  ltjspincludegt ltJSPforwardgt or jspparams block
• Example
• ltjspinclude page"login.jsp"gt
• ltjspparam name"username" value"jsmith" /gt
• lt/jspincludegt

Executes a login page jspparam passes in
username to the login page
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JSP Action Elements
JSP pre-defined tags (standard actions elements)
Done
External Tag library -------? Custom
-------? Java Standard tag library
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JSP Action elements External tag libraries
custom

• JSP 1.1. introduced tag libraries, allowing
  addition of tags beyond standard action ltjsp gt
  tags
• Developers can develop their own Custom action
  elementsusing custom tag libraries
• Custom tag libraries are useful where developers
  are working in teams reusabletags can be
  supplied to team via custom tag libraries.
• The library is identified in the JSP page using
  the lttaglibgtdirective

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JSP Action elements External tag libraries
custom
Example of custom tag library supplied with
Blazix web server
Prefix to be used Library location
lt_at_ taglib prefix"blx" uri"/blx.tld"
gt ltjspuseBean id"user" class"UserData"
scope"session"/gt ltHTMLgt ltBODYgt
ltblxgetProperty name"user" property""gt
ltFORM METHODPOST ACTION"SaveName.jsp"gt
Your name? ltINPUT TYPETEXT NAMEusernamegtltBRgt
Your e-mail address? ltINPUT TYPETEXT
NAMEemailgtltBRgt Your age? ltINPUT TYPETEXT
NAMEage SIZE4gt ltPgtltINPUT
TYPESUBMITgt lt/FORMgt lt/blxgetPropertygt
lt/BODYgt lt/HTMLgt
Tag from tag library
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JSP Action Elements
JSP pre-defined tags (standard actions elements)
Done
External Tag library -------? Custom
Done -------? Java Standard tag library