protected void doPost(HttpServletRequest request, HttpServletResponse response)若param是json字符串
用request.getParameterMap()获取到的Map key是json串，value值为空；若用request.getInputStream()来获取参数则是直接获取到json字符串
若param是key=value&key=value…类型的字符串（此时传的就不是json串了）用request.getParameterMap()正常获取，若用request.getInputStream()获取到的是key=value&key=value.....字符串
