1.判断是不是ajax请
X-Requested-With: XMLHttpRequest
request.getHeader("X-Requested-With")！=null&&request.getHeader("X-Requested-With").equels（XMLHttpRequest）
true为ajax请求
1.请求
request.getRequestURI() 返回值类似：/xuejava/requestdemo.jsp
request.getRequestURL() 返回值类似：http://localhost:8080/xuejava/requestdemo.jsp
request.getRequestURL() 返回值类似：http://localhost:8080/xuejava/requestdemo.jsp