Servlet e web.xml

String comando = request.getParameter("comando");

if(comando.equals("listar")){

        RequestDispatcher rd = request.getRequestDispatcher("listar.jsp");
        rd.forward(request, response);

} else if(comando.equals("menu")){
              response.sendRedirect("index.html");
}

<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns="http://java.sun.com/xml/ns/j2ee"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
	http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
	version="2.4">
	
	<servlet>
		<servlet-name>Cadastro</servlet-name>
		<servlet-class>br.com.servlet.CadastroServlet</servlet-class>
	</servlet>

	<servlet-mapping>
		<servlet-name>Cadastro</servlet-name>
		<url-pattern>/processa</url-pattern>
	</servlet-mapping>
</web-app>

<a href="processa?comando=listar">