用户登录时，将用户信息放到session中

package cn.woniubushiniu.controller;

import cn.woniubushiniu.po.User;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

import javax.servlet.http.HttpSession;

@Controller
public class UserController {
    /**
     * 向用户登录页面跳转
     */
    @RequestMapping(value = "/login",method = RequestMethod.GET)
    public String toLogin(){
        return  "login";
    }

    /**
     * 用户登录
     * @param user
     * @param model
     * @param session
     * @return
     */
    @RequestMapping(value = "/login",method = RequestMethod.POST)
    public String login(User user, Model model, HttpSession session){
        //获取用户名和密码
        String username=user.getUsername();
        String password=user.getPassword();
        //些处横板从数据库中获取对用户名和密码后进行判断
        if(username!=null&&username.equals("admin")&&password!=null&&password.equals("admin")){
            //将用户对象添加到Session中
            session.setAttribute("USER_SESSION",user);
            //重定向到主页面的跳转方法
            return "redirect:main";
        }
        model.addAttribute("msg","用户名或密码错误，请重新登录！");
        return "login";
    }

    @RequestMapping(value = "/main")
    public String toMain(){
        return "main";
    }
    
    @RequestMapping(value = "/logout")
    public String logout(HttpSession session){
        //清除session
        session.invalidate();
        //重定向到登录页面的跳转方法
        return "redirect:login";
    }
    
}

拦截未登录的用户

public class LoginInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object o) throws Exception {
        //获取请求的RUi:去除http:localhost:8080这部分剩下的
        String uri = request.getRequestURI();
        //UTL:除了login.jsp是可以公开访问的，其他的URL都进行拦截控制
        if (uri.indexOf("/login") >= 0) {
            return true;
        }
        //获取session
        HttpSession session = request.getSession();
        User user = (User) session.getAttribute("USER_SESSION");
        //判断session中是否有用户数据，如果有，则返回true，继续向下执行
        if (user != null) {
            return true;
        }
        //不符合条件的给出提示信息，并转发到登录页面
        request.setAttribute("msg", "您还没有登录，请先登录！");
        request.getRequestDispatcher("/WEB-INF/jsp/login.jsp").forward(request, response);
        return false;
    }

    @Override
    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {

    }

    @Override
    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {

    }
}

配置文件
配置到spring 的配置文件中

<!--登录拦截器-->
        <mvc:interceptor>
            <mvc:mapping path="/**"/>
            <bean class="cn.woniubushiniu.interceptor.LoginInterceptor"/>
        </mvc:interceptor>
    </mvc:interceptors>
    

配置web.xml 拦截所有url,并设置需要扫描的spring文件

<!--配置前端控制器-->
    <servlet>
        <servlet-name>springmvc</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc-config.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>springmvc</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
    

小知识点，用来复习的~~