How are you sending this parameter through the URL?
% is a special escape character in a URL as well.
Just typing it into the address bar won't work.
http://www.blooberry.com/indexdot/html/topics/urlencoding.htm Take a look at the class java.net.URLEncoder.
The code you have here wouldn't cause the jsp to fail compilation.
It might create a problem with displaying the HTML but I don't think it would have an issue.
What is the actual error/problem you have?
What do you do with the variable "a" ?