request.getParameter()和request.getAttribute()的返回值request.getParameter(name)返回String类型，re
request.getParameter()和request.getAttribute()的返回值
request.getParameter("name")返回String类型，request.getAttribute("name")返回object类型
无论是request.getParameter("name")还是request.getAttribute("name"),如果在上下文中没有name的话，都会返回null值