Java Enterprise Best Practices

Always Include the <uri> Element in the TLD

The <uri> element in a JSP Tag Library Descriptor (TLD) is an optional element, intended for defining a default URI for the tag library that an authoring tool can use when generating JSP elements:

 . . . 
<taglib>
  <tlib-version>1.0</tlib-version>
  <jsp-version>1.2</jsp-version>
  <short-name>c</short-name>
  <uri>http://java.sun.com/jstl/core</uri>
  <display-name>JSTL core</display-name>
  <description>JSTL 1.0 core library</description>
   . . .

The auto-discovery feature introduced in JSP 1.2 relies on the presence of this otherwise optional element, however. During application startup, the JSP container scans all files in the application’s WEB-INF directory (including the content of JAR files) to locate all TLD files. For each TLD it finds, it looks for a <uri> element and records an implicit mapping between the URI and the location of the TLD file. Therefore, all you need to do to use the library is specify this default URI in the taglib directive; the container figures out from its mappings where the corresponding TLD file is. This dramatically simplifies tag library deployment over the mechanisms available in JSP 1.1, so you should always specify a default URI in the TLD for tag libraries you develop.