Actual combat in ThreadLocal project

        ThreadLocal The function of is to share data in the same thread , Every request in the project comes in , It is the same thread from beginning to end , In the same thread, if the data put in memory by the previous thread is to be shared with the next thread , Then you can use it ThreadLocal

        ThreadLocal The core principle of is , At the bottom of it is a Map<Thread,Object> threadLocal structure

/**
 *  Before executing the target method , First judge the user login status . And encapsulate user information to Controller
 */
public class CartInterceptor implements HandlerInterceptor {

    public static ThreadLocal<UserInfoTo> threadLocal = new ThreadLocal<>();

    /*
     Intercept before target method 
     */
    @Override
    public boolean preHandle(HttpServletRequest request,
                             HttpServletResponse response,
                             Object handler) throws Exception {

        UserInfoTo userInfoTo = new UserInfoTo();
        HttpSession session = request.getSession();
        MemberRespVo member = (MemberRespVo) session.getAttribute(AuthServerConstant.LOGIN_USER);
        if (member != null) {
            // The user login 
            userInfoTo.setUserId(member.getId());
        }
        Cookie[] cookies = request.getCookies();
        if (cookies != null && cookies.length > 0) {
            for (Cookie cookie : cookies) {
                String name = cookie.getName();
                if (name.equals(CartConstant.TEMP_USER_COOKIE_NAME)) {
                    userInfoTo.setUserKey(cookie.getValue());
                    userInfoTo.setTempUser(true);
                }
            }
        }
        // Before the target method is executed 
        // If there are no temporary users , Assign temporary users 
        if (StringUtils.isEmpty(userInfoTo.getUserKey())) {
            String uuid = UUID.randomUUID().toString();
            userInfoTo.setUserKey(uuid);
        }
        threadLocal.set(userInfoTo);
        return true;
    }

    /*
     After business execution   Assign temporary users 
     */
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable ModelAndView modelAndView) throws Exception {
        UserInfoTo userInfoTo = threadLocal.get();
        // If there is no information , Create temporary user , preservation cookie
        if (!userInfoTo.isTempUser()) {
            Cookie cookie = new Cookie(CartConstant.TEMP_USER_COOKIE_NAME, userInfoTo.getUserKey());
            cookie.setDomain("gulimall.com");
            // Unit second 
            cookie.setMaxAge(CartConstant.TEMP_USER_COOKIE_TIMEOUT);
            response.addCookie(cookie);
        }
    }
}