javax.servlet.forward AND javax.servlet.include

from servlet spec

requestURI = contextPath + servletPath + pathInfo

Include

When you include a servlet the following attributes will be set by the calling servlet
the attributes will be derived from the string you passed to include the servlet

javax.servlet.include.request_uri
javax.servlet.include.context_path
javax.servlet.include.servlet_path
javax.servlet.include.path_info
javax.servlet.include.query_string

ex:
first.jsp code
=========
rd = request.getRequestDispatcher("/myapp/second.jsp?pname=pvalue");
rd.include(request,response);
assume the context for your webapp is "myapp"

javax.servlet.include.request_uri : /myapp/second.jsp
javax.servlet.include.context_path : /myapp
javax.servlet.include.servlet_path : /second.jsp
javax.servlet.include.path_info : null
javax.servlet.include.query_string : pname=pvalue


Forward

when you forward to a servlet the following attributes will be set by calling servlet

javax.servlet.forward.request_uri = request.getRequestURI() value in the calling servlet
javax.servlet.forward.context_path = request.getContextpath() value in the calling servlet
javax.servlet.forward.servlet_path = request.getServletpath() value in the calling servlet
javax.servlet.forward.path_info = request.getPathInfo() value in the calling servlet
javax.servlet.forward.query_string = request.getQueryString() value in the calling servlet

ex:
first.jsp code
=========
rd = request.getRequestDispatcher("/myapp/second.jsp?pname=pvalue");
rd.forward(request,response);
assume the context for your webapp is "myapp"

Access URL is: http://localhost:8080/myapp/first.jsp?first=first

javax.servlet.forward.request_uri : /myapp/first.jsp
javax.servlet.forward.context_path : /myapp
javax.servlet.forward.servlet_path : /first.jsp
javax.servlet.forward.path_info : null
javax.servlet.forward.query_string : first=first


Is path_info is null always?

No.
This will come into picture when your servlet is matched by /* pattern in web.xml

ex:
your appication context is myapp and have 1 entries in web.xml for  a servlet with following mapping

Servlet Mapping Pattern: /lawn/*

and the request from client is

http://localhost:8080/myapp/lawn/grretings/d.html

here path info : /greetings/d.html
Servlet path   : /lawn