概念

拦截器有嘛用？
在用户登录时，防止页面跳转

代码

@Controller
public class mapper1 {
    @GetMapping("/")//
    public String skip(){
        return "index";
    }
    @GetMapping("/login")
    public String false1(HttpServletRequest req){
        HttpSession session = req.getSession();
        session.setAttribute("user",1);
        return "false";
    }
}

public class AdminInterceptor1 implements HandlerInterceptor {//继承HandlerInterceptor
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        String user = (String)request.getSession().getAttribute("user");
        if(user!=null){//判读用户是不是已经登录
            return true;
        }
        response.sendRedirect(request.getContextPath()+"/login");//没登录跳转到/login
        return false;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
//        HandlerInterceptor.super.postHandle(request, response, handler, modelAndView);
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
//        HandlerInterceptor.super.afterCompletion(request, response, handler, ex);
    }
}

@Configuration
public class LoginConfig implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        InterceptorRegistration regiest = registry.addInterceptor(new AdminInterceptor1());
        regiest.addPathPatterns("/**");//拦截所有路径
        regiest.excludePathPatterns( "/login");  //不拦截

    }
}