Creating EL-Aware Taglibs Using XDoclet
When the JSP Tag Extensions (also known as taglibs) first came out, the only option to pass dynamic values as tag attributes was using Request Time (RT) expressions. With the advent of JSTL 1.0, another option ha
Tutorial Details:
This article assumes the reader already understand how EL works -- if you don't, a good introduction can be found in Sue Spielman's article, "Practical JSTL, Part 1."
The following code shows an example of RT and EL usage. First, we use RT to get the name of a user that is stored in the application context, given its login, passed as a parameter:
<%
String userName = "";
Map tmpMap = (Map) application.getAttribute( "usersMap" );
if ( tmpMap != null ) {
User tmpUser = (User) tmpMap.get( request.getParameter("login") );
if ( tmpUser != null && tmpUser.getName() != null ) {
userName = tmpUser.getName();
} // inner if
} // outer if
%>
Welcome <%= userName >!
Using EL and JSP 2.0, the same thing can be done much more concisely:
Welcome ${applicationScope.usersMap[param.login].name}!
As you can see in the example above, it is much easier for the page author to use EL rather than RT. But it is harder for taglib developers to implement custom tags that handle EL, as they have to explicitly write code in the tag handlers to evaluate the EL expressions at runtime.
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