JSP and JSTL Tutorials - Tutorial Addendum - JSP Custom Tag

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 31 December 18:00   




(Continued from antecedent part...)



3. Autograph the tag library descriptor (tld) file. Now, I charge to ascertain a tag in a tag library


descriptor book to use the tag class. Actuality is my first tld file, HyTaglib.tld:




<?xml version="1.0"?>


<!DOCTYPE taglib Accessible


"-//Sun Microsystems, Inc.//DTD JSP Tag library 1.2//EN"


"http://java.sun.com/j2ee/dtds/web-jsptag library _1_2.dtd">


<!-- HyTaglib.tld


Absorb (c) 2003 by Dr. Yang










<short-name> s Tag Library</short-name>
















4. Installing the tld file. Tag library descriptor files charge to be attainable


by the bobcat server. So I affected HyTaglib.tld to


ootweb-inf lds directory.



5. Autograph the JSP page. To use my first custom tag, I wrote the afterward


JSP page, hello_tag.jsp:




<?xml version="1.0"?>


<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page"


xmlns:hy="urn:jsptld:/WEB-INF/tlds/HyTaglib.tld" version="1.2">


<!-- hello_tag.jsp


Absorb (c) 2003 by Dr. Yang




<jsp:directive.page import="HelloTag"/>


<jsp:directive.page contentType="text/html"/>












6. Examination the JSP page. To see the achievement of my JSP page, I affected hello_tag.jsp


to localjakarta-tomcat-4.1.18webapps
oot, started bobcat 4.1.18 server, and


use Internet Explorer (IE) to appearance http://localhost:8080/hello_tag.jsp.



7. I did get the "Hello world!" bulletin in the IE window. So my accost tag formed perfectly.



8. If you are alteration your tag chic afterwards it has been loaded by tomcat,


you may charge to restart tomcat, or bang "restart" on the "root" appliance


on the bobcat admin page. "root" appliance is area I put my JSP pages.



How Custom Tag Works



Here is my compassionate of how custom tag works, using the "Hello world!" tag as


an example:



  • When "hello_tag.jsp" page is requested for the first time, Bobcat server will


    translate the JSP page into a java class.



  • When the <hy:hello/> custom tag is encountered during the translation,


    Tomcat server will chase the tld book to locate the HelloTag.class file.


    Note that the tld book is provided in the "jsp:root" element.



  • Then Bobcat server will alter the custom tag with some Java cipher


    to instantiate an item of the tag class, initialize the object, and alarm


    the doStartTag() method.



  • To achievement data into page, you can get an achievement beck from the


    pageContext item provided by the JSP tag addendum facility, pageContext.getOut().


    This is how the "Hello world!" bulletin gets produced in the IE window.



  • Note that I accept to use "jsp:directive.page" to acceptation HelloTag chic into


    the JSP page, because my HelloTag chic has no Java amalgamation name and needs


    to be imported, even if it is amid in the chic path.







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