servlet过滤器

servlet过滤器原理

使用Filter的步骤：
1、在web.xml中增加Filter

<filter>
    <filter-name></filter-name>
    <filter-class></filter-class>
    <init-param>
      <param-name>url</param-name>
      <param-value>/admin/login.jsp</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name></filter-name>
    <url-pattern></url-pattern>
</filter-mapping>

2、import javax.servlet.Filter
init()
doFilter()
destroy()