Servlet实现了Filter接口,定义了如下方法:
- init():程序启动时调用此方法,用于初始化该Filter
- doFilter():客户请求服务器是会经过这里,是具体执行过滤器代码
- dostory():程序关闭时调用此方法
Filter的生命周期,init()和destroy()方法只被调用一次,doFilter()方法每次有客户端请求就会被调用一次
创建过滤器类FirstFilter类
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public class FirstFilter implements Filter {
private FilterConfig filterConfig;
@Override
public void destroy() {
this.filterConfig=null;
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
throws IOException, ServletException {
try{
System.out.println("客户端的请求经过这里!!!");
filterChain.doFilter(request,response);
System.out.println("账号和密码请求处理经过这里");
}catch(ServletException e){
System.out.println("客户端请求失败");
}catch(IOException io){
System.out.println("账号和密码请求失败");
}
}
@Override
public void init(FilterConfig filterConfig) throws ServletException {
this.filterConfig=filterConfig;
}
}
在web.xml中配置过滤器
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<filter>
<filter-name>firstFilter</filter-name><!--过滤器名称 -->
<filter-class>com.cn.zj.ServletFilter.FirstFilter</filter-class><!--过滤器的实现类 -->
</filter>
<filter-mapping>
<filter-name>firstFilter</filter-name> <!--映射过滤器名称 -->
<url-pattern>/*</url-pattern><!--使用通配符*什么请求都经过滤器 -->
</filter-mapping>
**index.js页面**
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>创建过滤器</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
请重新刷卡登录!!!
</body>
</html>