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Java for the WWW Tag Libraries • What are they? – Custom libraries • Custom tags – see examples in following slides – Standard Tag Library (JSTL) – recommend that you read the following: • http://today.java.net/pub/a/today/2003/10/07/jstl1.html • http://today.java.net/pub/a/today/2003/11/27/jstl2.html • Purpose and benefits for JSP web development – Lot of development and includes the AJAX technology but this is outside the scope of this module • For further reading on Tag libraries – here is nice tutorial to back up the following notes <link> November 2012 [email protected] Slide 1 Java for the WWW Custom tags • Custom tags are dynamic page elements. • This means they can provide functionality to a web page using a syntax similar to normal HTML tags. • The functionality is up to you… • They can provide an alternative (or an additional) mechanism to JavaBeans for dynamic scripting. March 2009 [email protected] Slide 2 Java for the WWW What do you need? • There are two components to a tag: – A Java tag handler class that implements the tag’s functionality. – A Tag Library Descriptor (TLD) in the form of an XML file describing the tag. • By including this tag on a JSP page you have access to its functionality. March 2009 [email protected] Slide 3 Java for the WWW Java handler class • Yes, you have to code the functionality in Java. • So why bother? Why not just create a JavaBean instead? – For standard web page scripters, tags are more familiar and provide a simpler mechanism. – For web application developers, JavaBeans integrate more fully with the full application environment so are more powerful. • Your choice…. March 2009 [email protected] Slide 4 Java for the WWW Making the handler • You Java class needs to extend the TagSupport class. • This class is only available in the Enterprise version of the Java Development Kit (from version 1.3.1). • Or, the Java Web Services Developer Pack. • However, you just need the lib/j2ee.jap file (in the case of J2EE) or the lib/servlet.jar for the JWSDP. • You can then extract the javax.servlet.jsp.tagext class from the .jar file (using WinZip etc.) and put it into folder containing your tag classes – see screen grab on next powerpoint March 2009 [email protected] Slide 5 Java for the WWW March 2009 [email protected] Slide 6 Java for the WWW Making the handler • Once you have your custom tag Java code, you need to compile it and put the resultant .class file in your WEB-INF/classes folder. • For the examples, this would go in: – WEB-INF/classes/mytags March 2009 [email protected] Slide 7 Java for the WWW Example handler March 2009 [email protected] Slide 8 Java for the WWW Tag Library Descriptor • A TLD is a (fairly) simple XML file that describes a set of custom tags. • You can put as many or as few custom tags in a TLD and more than one TLD can be used in a single project. • In principle, you could create many useful tags and zip them into one .jar file for easy reusability. March 2009 [email protected] Slide 9 Java for the WWW Example Tag Descriptor [email protected] Slide 10 Java for the WWW Using your custom tag • To use your custom tag, you need a JSP page. • You need to tell your JSP where to find your tag library so you use a page directive: <%@ taglib uri=“WEB-INF/nameofdescriptor.tld” prefix=“something” %> • Anywhere in your JSP page, you can then use your custom tag(s): March 2009 [email protected] Slide 11 Java for the WWW Example with a JSP March 2009 [email protected] Slide 12 Java for the WWW The use of tag libraries is all about... • Re-usability • Defining things once and making them available for use in more than one place • Simplification • Bespoke JSP work • Or using existing tag libraries available for use - See the following Jsptags.com Jspin Jakata Apache Taglibs project March 2009 [email protected] Slide 14