Packaging a JavaServer Pages[tm] (JSP[tm]) Tag Handler Class
with iPlanet[tm] Application Server, Enterprise Edition 6.0

by Matthew Hosanee
(June 2002)

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The following article may contain actual software programs in source code form. This source code is made available for developers to use as needed, pursuant to the terms and conditions of this license.

Overview

The XML document, Tag Library Descriptor (TLD) has an element <tagclass> (as per the JSP specifications 1.1/1.2 - see the Resources section of this article). This element is required by the specification and describes the location of the tag handler class in the form of a fully qualified Java[tm] programming language class name.

When shipping togther in a Web ARchive (WAR) file, the WEB-INF directory is used as follows:
WEB-INF
    Contains the web.xml file
WEB-INF/classes
    Contains the tag handler classes
WEB-INF/lib
    Contains the JAR files containing additional classes

A TLD file can be stored in the WEB-INF directory but also in a subdirectory of WEB-INF, and must have the extension .tld.

A simple example TLD file for a tag handler class MyTagTest.class could look like:

The TLD file element <tagclass> could suggest that the class lives in WEB-INF/classes/MyTagTest.class, following the documentation, guidelines and specification. However, when deploying the WAR, the JSP does not load and the kjs log reports:

[date time] error: APPLOGIC-caught_exception: Caught Exception:
java.lang.NullPointerException
        at com.netscape.server.servlet.platformhttp.PlatformHttpServletResponse.sendError(Unknown Source)
        at com.netscape.server.servlet.servletrunner.ServletRunner.reportError(Unknown Source)
        at com.netscape.server.servlet.servletrunner.ServletRunner.execute(Unknown Source)
        at com.kivasoft.applogic.AppLogic.execute(Unknown Source)
        at com.kivasoft.applogic.AppLogic.execute(Unknown Source)
        at com.kivasoft.thread.ThreadBasic.run(Native Method)
        at java.lang.Thread.run(Thread.java:484)
[date time] error: Exception: SERVLET-execution_failed: Error in executing servlet TagLibTest: java.lang.Exception: javac error: /my_install_dir/ias65/
ias/APPS/modules/MyWarName/WEB-INF/compiled_jsp/jsp/APPS/MyWarName/TagLibTest.java:65: Class jsp.APPS.MyWarName.MyTagTest not found.
                MyTagTest _jspx_th_mytablib_test_0 = new MyTagTest();
                ^
/my_install_dir/ias65/ias/APPS/modules/MyWarName/WEB-INF/compiled_jsp/jsp/APPS/MyWarName/TagLibTest.java:65: Class jsp.APPS.MyWarName.MyTagTest not found.
                MyTagTest _jspx_th_mytablib_test_0 = new MyTagTest();
                                                         ^
2 errors

Observing the logs you can see that the compiled JSP package is set as jsp.APPS.MyWarName.  The tag library MyTagTest is not being found in this package.

The solution is to put the tag handler class in a package, as all Java programming language classes should be. This is done to ensure the uniqueness of a fully qualified Java programming language class name. The class loader for Web applications in iPlanet Application Server is shared, so not using a package name could cause conflicts.

In this way the TLD <tagclass> element could look like:
<tagclass>mypackage.MyTagTest</tagclass>

Resources

The JSP 1.1/1.2 specification can be downloaded from
http://java.sun.com/products/jsp/download.html

The JSP 1.1 DTD can be found from
http://java.sun.com/j2ee/dtds/web-jsptaglibrary_1_1.dtd