code: public static void bind(HttpServletRequest request) {
          if (request != null && threadLocal.get() != null) {
              throw new IllegalStateException("HttpServletRequestHolder.bind() called for a "
                      + "thread that already has a request associated with it. It's likely that the request "
                      + "was not correctly removed from the thread before it is put back into the thread pool.");
          }
          threadLocal.set(request);
      }
docs: Associate the request with the current thread.