code: public String getActualDataSourceName(final String actualTableName) {
          Optional<TableRule> tableRule = findTableRuleByActualTable(actualTableName);
          if (tableRule.isPresent()) {
              return tableRule.get().getActualDatasourceNames().iterator().next();
          }
          if (!Strings.isNullOrEmpty(shardingDataSourceNames.getDefaultDataSourceName())) {
              return shardingDataSourceNames.getDefaultDataSourceName();
          }
          throw new ShardingException("Cannot found actual data source name of '%s' in sharding rule.", actualTableName);
      }
docs: Get actual data source name.
  
  @param actualTableName actual table name
  @return actual data source name