# 显示登录信息

---

## 定义拦截器（实现 HandlerInterceptor）

- 在请求开始时查询登录用户

- **在本次请求中持有用户数据**

  通过 `ThreadLocal` 把用户数据存入当前线程对应的 map 里，只要本次请求未处理完，这个线程就一直还在，当请求处理完即服务器对本次请求做出响应后，这个线程被销毁

- 在模板视图上显示用户数据

- 在请求结束时清理用户数据



![](https://gitee.com/veal98/images/raw/master/img/20210119110057.png)

```java
@Component
public class LoginTicketInterceptor implements HandlerInterceptor {

    @Autowired
    private UserService userService;

    @Autowired
    private HostHolder hostHolder;

    /**
     * 在 Controller 执行之前被调用
     * @param request
     * @param response
     * @param handler
     * @return
     * @throws Exception
     */
    @Override
    public 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) {
            // 查询凭证
            LoginTicket loginTicket = userService.findLoginTicket(ticket);
            // 检查凭证状态（是否有效）以及是否过期
            if (loginTicket != null && loginTicket.getStatus() == 0 && loginTicket.getExpired().after(new Date())) {
                // 根据凭证查询用户
                User user = userService.findUserById(loginTicket.getUserId());
                // 在本次请求中持有用户信息
                hostHolder.setUser(user);
            }
        }

        return true;
    }

    /**
     * 在模板引擎之前被调用
     * @param request
     * @param response
     * @param handler
     * @param modelAndView
     * @throws Exception
     */
    @Override
    public 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 Controller 执行之后（即服务端对本次请求做出响应后）被调用
     * @param request
     * @param response
     * @param handler
     * @param ex
     * @throws Exception
     */
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        hostHolder.clear();
    }
}
```



## 配置拦截器

```java
/**
 * 拦截器配置类
 */
@Configuration
public class WebMvcConfig implements WebMvcConfigurer {

    @Autowired
    private LoginTicketInterceptor loginTicketInterceptor;

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(loginTicketInterceptor)
                .excludePathPatterns("/css/**", "/js/**", "/img/**");
    }
}
```

## 前端

```html
<li th:if="${loginUser == null}">
	<a th:href="@{/register}">注册</a>
</li>

<img th:src="${loginUser.headerUrl}" />
```