Hi,
I've been using JSPs for quite a while now and have been trying to find
better ways to do various things. One of the features of JSPs that I
stumbled on a while ago was the ability to define methods in JSPs and to
be able to call those methods from within the page using Java Reflection
mechanisms. This works relatively well (see example below), except for
the baggage of having to do the reflection work. Alas, that is the
price we pay for a strongly typed language.
What I'm wondering is why more people don't use the declaration syntax
as a way to define methods in pages and use those methods to abstract
out some of the functionality they need? My answer would be that it is
generally frowned upon (by the MVC crowd) to put logic into the JSP page
and to a certain extent I agree. But, there are times where the logic
code is only used to modify the display and in those cases it seems to
me like putting that logic into a method within the JSP makes sense.
For example, when building the title string of the page you often have
to look up or build some sort of descriptive string from the various IDs
of the objects that are part of the request/session to the page. It
seems to me that doing this sort of operation is the kind of thing which
should be within the JSP page and using methods within the JSP page seem
to make even more sense as opposed to scriptlets. The alternatives are:
1) Put the "getPageTitle" method into the Model object. If the model is
supposed to capture the data of the object then it doesn't seem to me
like it should be cluttered with methods relevant to displaying the object.
2) Put the "getPageTitle" method into the Controller object. Again, if
the controller is the driver of the business logic of the object(s) then
it too doesn't seem like the right place for methods relevant to
displaying the object.
It seems like using methods in JSP pages is a good idea for certain
things. It also has it's downsides, the main one that I see is that
there is no inheritance among JSP pages. I wonder how hard this would
be to add?
Does any one have any comments about why defining methods in JSP pages
is a good or bad idea? I would really appreciate hearing from you.
Thanks for you time.
Alex.
***************
Example method in a JSP page:
***************
<%@ page language="java" import="java.lang.reflect.*" %>
<%!
public String getTitle(HttpServletRequest request) {
String id = request.getParameter("id");
return "id: " + id;
}
%>
<% Class c = this.getClass();
// The types for the method call
Class [] pTypes = new Class [1];
Class hsr = Class.forName("javax.servlet.http.HttpServletRequest");
pTypes[0] = hsr;
// Get the method
Method m = c.getMethod("getTitle", pTypes);
// Build the list of parameters to the method
Object [] params = new Object [1];
params[0] = request;
// Invoke the method and get the result
String result = (String) m.invoke(this, params);
%>
Method Result: <%= result %>
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