(二十四)权限控制(粗粒度)-通过filter

扩展:权限控制(粗粒度)-通过filter
过滤器编写步骤:
    1.编写一个类
        实现filter接口
        重写方法
    2.编写配置文件
        <filter>
        <filter-mapping>
        
    编写一个privilegeFilter
        判断用户是否登录(session)
        若为空 
            请求转发到msg.jsp 携带信息

package com.louis.web.filter;

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;
import javax.servlet.http.HttpServletResponse;

import com.louis.dao.UserDao;
import com.louis.domain.User;

public class PrivilegeFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain)
            throws IOException, ServletException {
        //1.强转
        HttpServletRequest request=(HttpServletRequest) req;
        HttpServletResponse response=(HttpServletResponse) resp;
        
        //2.业务逻辑
        //从session中获取user 判断user是否为空 若为空 请求转发
        User user=(User) request.getSession().getAttribute("user");
        if(user==null){
            request.setAttribute("msg", "没有权限,请先登录!");
            request.getRequestDispatcher("/jsp/msg.jsp").forward(request, response);
            return;
        }
        
        //3.放行
        chain.doFilter(request, response);
    }

    @Override
    public void destroy() {
        // TODO Auto-generated method stub

    }

}

<filter>
      <filter-name>PrivilegeFilter</filter-name>
      <filter-class>com.itheima.web.filter.PrivilegeFilter</filter-class>
  </filter>
  <filter-mapping>
      <filter-name>PrivilegeFilter</filter-name>
      <servlet-name>OrderServlet</servlet-name>
      <url-pattern>/jsp/order_info.jsp</url-pattern>
      <url-pattern>/jsp/order_list.jsp</url-pattern>
      <!-- <url-pattern>/jsp/cart.jsp</url-pattern> -->
  </filter-mapping>