title: Why shouldn't we place tomcat library in our appln libraries
body: <p>I have a web application running in Tomcat 7.
  When I place the tomcat default libraries (jsp-api.jar,servlet-api.jar etc.) in my application/WebContent/WEB-INF/lib, it throws an exception : <code>java.lang.IllegalStateException: No org.apache.tomcat.InstanceManager set in ServletContext</code></p>
  
  <p>When I delete these jars from my lib and and set tomcat lib in build.xml, it works fine. Can anyone explain to me why this happens?
  Why can't I use tomcat libraries in my lib folder?</p>