what are the difficulties with expression language? and where we use the user interface in the jsp can you explain it with a good example(inside that user interface must be available) so that i can understand?
If you are asking if there are limitations to the Expression Language, then, yes there are. And they are deliberate.
The Expression Language, in concert with the JSTL, is intended to usher in an age where JSP pages are solely used as scriptless view units for a web app, with all control, processing and computational processes occurring outside the view.
Essentially, the intentional limitations serve as a "red flag". If you are finding that it's difficult to do something on a JSP page using just JSTL and EL, there's a good chance that it's something you shouldn't be doing there.
This requires that an appropriate web application structure, such as Model 2, is in place. This article goes into that.
Let me just say, THANK GOD FOR THE EL FAQ IN JAVARANCH!
I have been grinding away on an EL problem all day long (why my EL won't resolve), only to find that my Web.xml has been at version 2.5 but I'm deploying to Tomcat 5.5.26 which only supports 2.4. Duh! (Sound of hand slapping forehead) The servers at Google must be smoking hot with all the search requests I've made to no avail today.