code: private Connection getConnection() {
          final JdbcTransaction jdbcTransaction = TX.get();
          if (null != jdbcTransaction && jdbcTransaction.isActive()) {
              return jdbcTransaction.getConnection();
          }
  
          Connection ret = CONN.get();
          try {
              if (null != ret && !ret.isClosed()) {
                  return ret;
              }
  
              ret = Connections.getConnection();
          } catch (final SQLException e) {
              LOGGER.log(Level.ERROR, "Gets a connection failed", e);
          }
  
          CONN.set(ret);
  
          return ret;
      }
docs: getConnection. default using current JdbcTransaction's connection, if null get a new one.
  
  @return {@link Connection}