java - ThreadLocal

介绍

在 Tomcat 中，每个请求都是一个线程，可以在该线程中存储一些数据

示例

说明:

• 在登录拦截器中 取出 Session 中的 user 存入 ThreadLocal ，后续可以直接从 ThreadLocal 中取 user

@Slf4j
public class LoginInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        // 1. 获取 session
        HttpSession session = request.getSession();

        // 2. 获取 session 中的用户
        Object user = session.getAttribute("user");

        // 3. 用户不存在，拦截 并返回 401 或抛异常
        if (user == null) {
            log.info("用户不存在");
            response.setStatus(401);
            return false;
        }

        // 4. 用户存在，存入 ThreadLocal
        UserDTO userDTO = BeanUtil.copyProperties(user, UserDTO.class);
        UserHolder.saveUser(userDTO);

        // 5. 放行
        return true;
    }

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


public class UserHolder {
    private static final ThreadLocal<UserDTO> tl = new ThreadLocal<>();

    public static void saveUser(UserDTO user){
        tl.set(user);
    }

    public static UserDTO getUser(){
        return tl.get();
    }

    public static void removeUser(){
        tl.remove();
    }
}

@Data
public class UserDTO {
    private Long id;
    private String nickName;
    private String icon;
}