过滤器应用

需求：访问服务器资源时，需要先进行登录验证，如果没有登录，则自动跳转到登录页面

核心代码：

package com.itheima.web.filter;
 
import javax.servlet.*;
import javax.servlet.annotation.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import java.io.IOException;
 
/**
 * 登录验证的过滤器
 */
 
@WebFilter("/*")
public class LoginFilter implements Filter {
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException {
        HttpServletRequest req = (HttpServletRequest) request;
        //判断访问资源路径是否和登录注册相关
        String[] urls = {"/login.jsp","/imgs/","/css/","/loginServlet","/register.jsp","/registerServlet","/checkCodeServlet"};
        // 获取当前访问的资源路径
        String url = req.getRequestURL().toString();
 
        //循环判断
        for (String u : urls) {
            if(url.contains(u)){
                //找到了
                //放行
                chain.doFilter(request, response);
                //break;
                return;
            }
        }
 
 
        //1. 判断session中是否有user
        HttpSession session = req.getSession();
        Object user = session.getAttribute("user");
 
        //2. 判断user是否为null
        if(user != null){
            // 登录过了
            //放行
            chain.doFilter(request, response);
        }else {
            // 没有登陆，存储提示信息，跳转到登录页面
 
            req.setAttribute("login_msg","您尚未登陆！");
            req.getRequestDispatcher("/login.jsp").forward(req,response);
        }
 
 
    }
 
 
    public void init(FilterConfig config) throws ServletException {
    }
 
    public void destroy() {
    }
 
 
}