流程：从cookie中获取凭证，根据凭证查询用户，并在本次请求中持有用户，在视图模板上显示登录用户的信息。

1. 定义拦截器

package com.nowcoder.community.controller.Interceptor;import com.nowcoder.community.entity.LoginTicket;
import com.nowcoder.community.entity.User;
import com.nowcoder.community.service.UserService;
import com.nowcoder.community.util.CookieUtil;
import com.nowcoder.community.util.HostHolder;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.Date;@Componentpublic class LoginTicketInterceptor implements HandlerInterceptor {@Autowiredprivate UserService userService;@Autowiredprivate HostHolder hostHolder;@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {// 从cookie中获取凭证String ticket = CookieUtil.getValue(request, "ticket");if(ticket != null){  // 已经登陆LoginTicket loginTicket = userService.findLoginTicket(ticket);// 检查ticket是否有效if(loginTicket != null && loginTicket.getExpired().after(new Date()) &&loginTicket.getStatus()==0){// 根据凭证查询用户User user = userService.findUserById(loginTicket.getUserId());// 在本次请求中持有用户hostHolder.setUsers(user);}}return true;}// 在模板引擎之前使用user，将user放到model里@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {User user = hostHolder.getUser();if(user != null && modelAndView != null){modelAndView.addObject("loginUser",user);}}// 在模板引擎启动后清掉threadlocal，防止内存泄露@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {hostHolder.clear();}
}

2. 配置拦截器

package com.nowcoder.community.config;import com.nowcoder.community.controller.Interceptor.AlphaInterceptor;
import com.nowcoder.community.controller.Interceptor.LoginTicketInterceptor;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;@Configurationpublic class WebMvcConfig implements WebMvcConfigurer {@Autowiredprivate AlphaInterceptor alphaInterceptor;@Autowiredprivate LoginTicketInterceptor loginTicketInterceptor;@Overridepublic void addInterceptors(InterceptorRegistry registry) {// 通过重写addInterceptors()方法，可以配置拦截器，对请求进行预处理或后处理。registry.addInterceptor(alphaInterceptor).excludePathPatterns("/**/*.css", "/**/*.js", "/**/*.png", "/**/*.jpg", "/**/*.jpeg").addPathPatterns("/register","/login");registry.addInterceptor(loginTicketInterceptor).excludePathPatterns("/**/*.css", "/**/*.js", "/**/*.png", "/**/*.jpg", "/**/*.jpeg");}
}