项目结构：
AFilter：
package cn.itcast.web.filter;
import javax.servlet.*; import java.io.IOException; public class AFilter implements Filter { /** * init方法在filter创建之后立即执行，用来做初始化 * @param filterConfig * @throws ServletException */ @Override public void init(FilterConfig filterConfig) throws ServletException { System.out.println("过滤器初始化！"); } /** * 每次过滤时都会执行 * @param servletRequest * @param servletResponse * @param filterChain * @throws IOException * @throws ServletException */ @Override public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { System.out.println("过滤器拦截。。。"); filterChain.doFilter(servletRequest, servletResponse); System.out.println("回来执行doFilter方法。。。"); } /** * destroy方法在销毁之前执行，用来对非内存资源释放 */ @Override public void destroy() { System.out.println("过滤器销毁！"); } }
web.xml配置
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
version="3.1">
<servlet>
<servlet-name>AServlet</servlet-name>
<servlet-class>cn.itcast.web.servlet.AServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>AServlet</servlet-name>
<url-pattern>/AServlet</url-pattern>
</servlet-mapping>
<filter>
<filter-name>AFilter</filter-name>
<filter-class>cn.itcast.web.filter.AFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>AFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
</web-app>
index.jsp页面
<%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>Title</title> </head> <body> <%System.out.println("执行index.jsp。。。");%> index.jsp页面 </body> </html>
控制台输出：
项目启动时执行init方法
访问index.jsp，http://localhost:8080/day09/index.jsp
执行doFilter方法
关闭服务器销毁filter
销毁filter之前会调用destroy方法