JSP problem deploying a java web application in tomcat -

I am learning ANT and I'm trying to install a web application in Pocket 6.0.20 server. I create test applications and I keep it with manager ant functions and everything goes well. I load an HTML page and it works ... When I try to see a JSP Tomcat, I have a Jasper Expansion, which is an HTML file with an NullPointerException JSP almost JSP extension in the auto-generated circlet . The exception is thrown in the _jspInit method when it tries to run the following: _el_expressionfactory = _jspxFactory.getJspApplicationContext (getServletConfig (). GetServletContext ()). GetExpressionFactory (); Anyone can help me? Thanks!

Maybe you have jsp-api- *. Jar in / web-INF / lib . Remove it.

Edit : Explanation

The JSP API has an abstract class JspFactory . In this there is a stable field to store a server-specific JspFactory implementation, then Tomcat sets a value for this field and the JSP page initialization code can be found in the JspFactory reads to get the implementation. In your case, you have two separate JspFactory classes - the servers have been loaded by the server classloader from the server and the second / WEB- Loaded by application classloader from INF / lib Ia is. Because the classes loaded by different classloaders are different classes, they have different stable field values, so the received by JSP code ( _jspxFactory ) Is jspfactory code> null .

This shows one of the potential problems due to the use of the stable areas.