1, Scene

• The life cycle of the container t thread pool is different from that of the request, so the ThreadLocal parameter isolation of the request domain cannot be saved
• The request domain needs to reclaim ThreadLocal manually every time. The solution of custom thread pool will not be considered temporarily
• For classes with unsafe threads such as simpleDateFormat and DecimalFormat, set scope to ensure thread safety, and avoid repeatedly creating and wasting memory space

2, Solutions

• Interceptor Based ThreadLocal collector
• ThreadLocal auto clean up registration
• Tags for HTTP requests

@NoArgsConstructor(access = AccessLevel.PRIVATE)
public class ThreadLocalCleaner {

    private static final List<ThreadLocal<?>> CONTAINER = Lists.newArrayList();

    public static void register(ThreadLocal<?>... threadLocal) {
        if(ArrayUtils.isNotEmpty(threadLocal)) {
            // Can be optimized
            CONTAINER.addAll(Arrays.asList(threadLocal));
        }
    }

    public static void clear() {
        CONTAINER.forEach(ThreadLocal::remove);
    }
}

public class ThreadLocalInterceptor extends HandlerInterceptorAdapter {

    /**
     * Whether it is a thread from http
     */
    private static final ThreadLocal<Boolean> IS_HTTP_REQUEST = new ThreadLocal<>();

    static {
        ThreadLocalCleaner.register(IS_HTTP_REQUEST);
    }

    public static boolean isHttpReqThread() {
        return Boolean.TRUE.equals(IS_HTTP_REQUEST.get());
    }

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        //thread local set
        IS_HTTP_REQUEST.set(Boolean.TRUE);
        return super.preHandle(request, response, handler);
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        //thread local remove
        ThreadLocalCleaner.clear();
        super.afterCompletion(request, response, handler, ex);
    }

}