code: public static UriComponentsBuilder getBuilder() {
  
  		if (RequestContextHolder.getRequestAttributes() == null) {
  			return UriComponentsBuilder.fromPath("/");
  		}
  
  		URI baseUri = getCachedBaseUri();
  
  		return baseUri != null //
  				? UriComponentsBuilder.fromUri(baseUri) //
  				: cacheBaseUri(ServletUriComponentsBuilder.fromCurrentServletMapping());
  	}
docs: Returns a {@link UriComponentsBuilder} obtained from the current servlet mapping with scheme tweaked in case the
  request contains an {@code X-Forwarded-Ssl} header. If no {@link RequestContextHolder} exists (you're outside a
  Spring Web call), fall back to relative URIs.
  
  @return