例如请求路径：http://localhost:8080/kefuwebsocket/servlet/DemoServlet
端口: 8080
request.getServerPort()；
服务器: localhost
request.getServerName()；
项目名: kefuwebsocket
request.getContextPath()；
ServletPath: servlet/DemoServlet
request.getServletPath()；
RequestURI: kefuwebsocket/servlet/DemoServlet
request.getRequestURI()；
整个请求路径:” http://localhost:8080/kefuwebsocket/servlet/DemoServlet
request.getRequestURL()
项目的路径：”D:\Tomcat7.0\webapps\kefuwebsocket”
request.getSession().getServletContext().getRealPath(“”)
