RequestDispatcher rd = request.getRequestDispatcher(urlToServlet);
rd.include(request, response);
The code above invokes the urlToServlet.
The called servlet processes the request and generates a new response back to a client.
A client browser will display the urlToServlet in the location line.

RequestDispatcher rd = request.getRequestDispatcher(urlToServlet);
rd.include(request, response);
rd.forward(request, response);
The forward() method should always follow one or more include() methods if additional content is included.

RequestDispatcher rd = request.getRequestDispatcher(urlToServlet);
rd.include(request, response);
The code above invokes the urlToServlet and the called servlet can only alter
the body of the response, and not the headers.
The path information of the request will reflect the original request location.

RequestDispatcher rd = request.getRequestDispatcher(urlToHtmlPage);
rd.forward(request, response);
The forward method in this example forwards to a client browser another web page with the urlToHtmlPage.

RequestDispatcher rd = request.getRequestDispatcher(urlToServlet);
rd.forward(request, response);
The forward method transfers control to the urlToServlet.
The called servlet can adjust the headers as well as the body of the response.
The path information of the request will reflect the location of the latest servlet.