support for sorting about rsql-parser HOT 1 OPEN

	@GetMapping("search")
	public ResponseEntity<List<ProductDTO>> searchProducts(
			@RequestParam(value = "query", required = false, defaultValue = "") String query,
			@Parameter(hidden = true) Pageable pageable,
			HttpServletRequest request) {
		Specification<Product> spec = Specification.where(null); 
		if(!StringUtils.isBlank(query)) {
			Node rootNode = new RSQLParser().parse(query);
			spec = rootNode.accept(new CustomRsqlVisitor<Product>());
		}
		Page<ProductDTO> page = service.searchProducts(spec, pageable);
		HttpHeaders headers = PaginationUtil.generatePaginationHttpHeaders(page, request.getRequestURI());
		headers.setAccessControlExposeHeaders(Arrays.asList(HttpHeaders.LINK, "X-Total-Count"));
		return new ResponseEntity<>(page.getContent(), headers, HttpStatus.OK);
	}