说明：  Ajax应用(jsp例子) 首先是jsp页面和脚本，为了方便写在一个里面 这是一个很常见的检测用户名是否存在的功能 这里用的是struts
(Ajax application (jsp example) is the first jsp page and the script, in order to facilitate a written inside this is a very common user name detection function of whether there is here is the struts)