code: @RequestMapping(path = "/{productId}", method=RequestMethod.GET)
      public ResponseEntity<Product> getCustomer(@PathVariable("productId") Long productId){
          Product product = productService.getProduct(productId);
          if(product != null){
              return new ResponseEntity<Product>(product, HttpStatus.OK);
          }
          return new ResponseEntity<Product>(HttpStatus.NOT_FOUND);
      }
docs: Get a specific product by id
  @param productId id of the product
  @response 200
  @response 404 if product doesn't exists
  @return the product or null