Win a copy of The Little Book of Impediments (e-book only) this week in the Agile and Other Processes forum!
  • Post Reply
  • Bookmark Topic Watch Topic
  • New Topic

The Listener In the Tag Library Descriptor

 
JiaPei Jen
Ranch Hand
Posts: 1309
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
<!ELEMENT taglib (tlib-version, jsp-version, short-name, uri?, display-name?,
small-icon?, large-icon?, description?, validator?, listener*, tag+) >
I am unable to find out what the listeners are in the Tag Library Descriptor, and my second question is whether there is any connection between the listeners in the Tag Library Descriptor and those listed preceding the <servlet> element in the DD of the web-xml?
<!ELEMENT web-app (icon?, display-name?, description?,
distributable?, context-param*, filter*, filter-mapping*,
listener*, servlet*, servlet-mapping*, session-config?, mime-
mapping*, welcome-file-list?, error-page*, taglib*, resource-
env-ref*, resource-ref*, security-constraint*, login-config?,
security-role*, env-entry*, ejb-ref*, ejb-local-ref*)>
I am hoping someone could help.
 
Velmurugan Periasamy
Ranch Hand
Posts: 95
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
I think both are same, yet I don't know why they can also be specified in TLD.
------------------
Velmurugan Periasamy
Sun Certified Java Programmer
Sybase Certified EAServer Developer
----------------------
Study notes for Sun Java Certification
http://www.geocities.com/velmurugan_p/
 
Anonymous
Ranch Hand
Posts: 18944
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
This should answer your question. Section 7.1.2.2 of the JSP 1.2 Spec states:
"A container is required to locate all TLD files, read their listener elements, and treat the event listeners as extension of those listed in web.xml. The order in which the listeners are registered is undefined, but they are registered before application starts."
------------------
Miftah Khan
- Sun Certified Programmer for the Java� 2 Platform
- Sun Certified Web Component Developer for the Java� 2 Platform, Enterprise Edition
 
JiaPei Jen
Ranch Hand
Posts: 1309
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
But, what are those listeners in TLD and what is the exact connection between the listeners in TLD and the listeners in web.xml?
 
Anonymous
Ranch Hand
Posts: 18944
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
The event listeners in a TLD are treated as an "extension of those listed in web.xml". In other words, the same rules for the listener element in the web.xml file apply here. As in the web.xml file, the listener types allowed are ServletContextListener, ServletContextAttributeListener, HttpSessionListener, and HttpSessionAttributeListener.
Perhaps you're wondering why are listener definitions duplicated between the two files. Well, suppose you bought a tag library from some vendor, and this tag library requires that a certain listener be running in the web app. The vendor will probably include the listener class as part of a jar file to be installed in your WEB-INF/lib directory, and will register the listener class in the TLD file.
Then, when you deploy this tag library, you should not have to touch the web.xml file in order to register the listener.. it's already done in the TLD.
Hope this answers your question.
------------------
Miftah Khan
- Sun Certified Programmer for the Java� 2 Platform
- Sun Certified Web Component Developer for the Java� 2 Platform, Enterprise Edition
[This message has been edited by Miftah Khan (edited October 01, 2001).]
 
JiaPei Jen
Ranch Hand
Posts: 1309
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Thanks, Miftah.
 
  • Post Reply
  • Bookmark Topic Watch Topic
  • New Topic