过滤器是一个对象，可以传输请求或修改响应。它可以在请求到达Servlet/JSP之前对其进行预处理，而且能够在响应离开Servlet/JSP之后对其进行后处理 -Filter is an object, you can transmit or modify in response to the request. Request it can reach the Servlet/JSP pre-treatment before they, and can leave in response t