filter应用案例二：权限控制

filter可以用来进行权限控制，比如admin文件夹下的文件只允许管理员进入，那么，可以给admin文件夹加上一个过滤器：

简单代码示例：

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;
import javax.servlet.http.HttpServletRequest;
public class RCFilter implements Filter {
    public void destroy() {}
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req=(HttpServletRequest) request;
        String admin=(String) req.getSession().getAttribute("admin");    //查看管理员是否登录，这里只是用于演示，方便起见，用字符串代替管理员类
        if(admin==null)
        {
            System.out.println("您不是管理员，不得进入该页面！");    //管理员未登录，不放行
        }
        else chain.doFilter(request, response);            //放行
    }
    public void init(FilterConfig fConfig) throws ServletException {}
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
  <display-name></display-name>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  <filter>
    <display-name>RCFilter</display-name>
    <filter-name>RCFilter</filter-name>
    <filter-class>RCFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>RCFilter</filter-name>
    <url-pattern>/admin/*</url-pattern>
  </filter-mapping>
</web-app>