request.getRequestDispatcher() vs getServletContext().getRequestDispatcher()

request.getRequestDispatcher() vs getServletContext().getRequestDispatcher()

Is there a different between both RequestDispatcher?

There is a small difference: 

From ServletRequest 

method to call: getRequestDispatcher(String path)

the path parameter doesn't have to start with a "/"

without a "/" it is relative to directory containing the Servlet. It doesn't have to exist as a real directory (because of the logical fiction of the servlet mapping)

cannot surpass the web-application

From ServletContext 

method to call: getRequestDispatcher(String path)

method to call: getNamedDispatcher(String name) - name should match a servlet-name

A servlet (identified with a servlet-name) without a servlet-mapping in the web.xml can be reached with the getNamedDispatcher()

the path parameter has to start with a "/", otherwise IllegalStateException

can surpass a web-application in the same server (JVM), using getContext() to obtain a foreign context. (note: Tomcat setting required in the servlet.xml: <Context crossContext="true"> )