code: public Referenceable getEntity(String guid) throws AtlasServiceException {
          JSONObject jsonResponse = callAPIWithBodyAndParams(API.GET_ENTITY, null, guid);
          try {
              String entityInstanceDefinition = jsonResponse.getString(AtlasClient.DEFINITION);
              return InstanceSerialization.fromJsonReferenceable(entityInstanceDefinition, true);
          } catch (JSONException e) {
              throw new AtlasServiceException(API.GET_ENTITY, e);
          }
      }
docs: Get an entity given the entity id
  @param guid entity id
  @return result object
  @throws AtlasServiceException