code: @GetMapping(value = "/{entityTypeId}/{id}", produces = APPLICATION_JSON_VALUE)
    public Map<String, Object> retrieveEntity(
        @PathVariable("entityTypeId") String entityTypeId,
        @PathVariable("id") String untypedId,
        @RequestParam(value = "attributes", required = false) String[] attributes,
        @RequestParam(value = "expand", required = false) String[] attributeExpands) {
      Set<String> attributesSet = toAttributeSet(attributes);
      Map<String, Set<String>> attributeExpandSet = toExpandMap(attributeExpands);
  
      EntityType meta = dataService.getEntityType(entityTypeId);
      Object id = getTypedValue(untypedId, meta.getIdAttribute());
      Entity entity = dataService.findOneById(entityTypeId, id);
      if (entity == null) {
        throw new UnknownEntityException(meta, id);
      }
  
      return getEntityAsMap(entity, meta, attributesSet, attributeExpandSet);
    }
docs: Get's an entity by it's id
  
  <p>Examples:
  
  <p>/api/v1/person/99 Retrieves a person with id 99