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DT228/3 Web Development

DT228/3 Web Development. JSP: Actions elements and JSTL. So far, have looked at these. 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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DT228/3 Web Development

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  1. DT228/3 Web Development JSP: Actions elements and JSTL

  2. So far, have lookedat these Introduction • Previously, identified that JSP provides a variety of techniques to enable dynamic processing: • Directive elements • Scripting elements • Action elements and JSTL • Java Beans

  3. 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 <%, they just use the < character (like HTML) <prefix:action_name>body </prefix:action_name >

  4. 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 < and > • The tag names have an embedded colon character “:” in them, the part before the colon (prefix) describes the type of the tag <prefix:action_name> body </prefix:action_name> • Part after the “:” is the Action Name • Note: Syntax of Action Elementags is based on XML

  5. JSP Action elements • Tags have associated attributes (like HTML e.g. <img src = “..”) • 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” /> For example: <jsp:include page="scripts/login.jsp" />

  6. JSP Action elements Two types 1. 2. JSP Pre-defined tags External tag library (e.g. JSTL) Tags prefix is <jsp: ….> Tags prefix is whatever developer chooses or library recommends Customand JSTL (Also called Standard Action Elements)

  7. JSP Action elements JSP pre-defined tags (standard actions elements) External Tag library: ------- Custom ------- Java Standard tag library

  8. JSP Action elements: JSP Predefined Tags • Also called JSP Standard Action Elements • List of these elements are:<jsp:forward> • <jsp:include> • <jsp:param> • <jsp:plugin> • <jsp:useBean> • <jsp:getProperty> • <jsp:setProperty> • See http://java.sun.com/products/jsp/syntax/1.1/syntaxref11.html for detailed attributes and values Used for Java Beans

  9. JSP Predefined Tag Example <jsp:include> • Standard Action Example: <JSP: include> tag • Example: • <HTML> <BODY> • Going to include hello.jsp...<BR> • <jsp:include page="hello.jsp"/> • </BODY> • </HTML> • Executes the included JSP page and adds its output into the this page

  10. JSP Predefined Tag Example <jsp:include> • What’s Difference from Using the ‘include’ directive?e.g. <%@ include file = ‘hello.jsp’ %> • 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

  11. JSP Predefined Tag Example <jsp:forward> • Standard Action Example: <JSP: forward> tag • Stops processing of one page and starts processing the page specified by the page attribute • Example: • <HTML> <BODY> • Error occurred…please wait<BR> • <jsp:forward page=“errorpage.jsp"/> • </BODY> • </HTML>

  12. JSP Predefined Tag Example <jsp:param> • Standard Action Example: <JSP: param> tag • Can be used to pass parameters when using <jsp:include> <JSP:forward> or jsp:params block • Example • <jsp:include page="login.jsp"> • <jsp:param name="username" value="jsmith" /> • </jsp:include> Executes a login page jsp:param passes in username to the login page

  13. JSP Action Elements JSP pre-defined tags (standard actions elements) Done External Tag library: ------- Custom ------- Java Standard tag library

  14. JSP Action elements: External tag libraries – custom • JSP 1.1. introduced ‘tag libraries’, allowing addition of tags beyond standard action <jsp: > 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 <taglib>directive

  15. JSP Action elements: External tag libraries – custom Example of custom tag library supplied with Blazix web server Prefix to be used Library location <%@ taglib prefix="blx" uri="/blx.tld" %> <jsp:useBean id="user" class="UserData" scope="session"/> <HTML> <BODY> <blx:getProperty name="user" property="*"> <FORM METHOD=POST ACTION="SaveName.jsp"> Your name? <INPUT TYPE=TEXT NAME=username><BR> Your e-mail address? <INPUT TYPE=TEXT NAME=email><BR> Your age? <INPUT TYPE=TEXT NAME=age SIZE=4> <P><INPUT TYPE=SUBMIT> </FORM> </blx:getProperty> </BODY> </HTML> Tag from tag library

  16. JSP Action Elements JSP pre-defined tags (standard actions elements) Done External Tag library: ------- Custom Done ------- Java Standard tag library

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