jetbrick-orm/src/main/java/jetbrick/dao/orm/DbHelper.java
private Connection getConnection() {
        JdbcTransaction tx = transationHandler.get();
        try {
            if (tx == null) {
                return dataSource.getConnection();
            } else {
                return tx.getConnection();
            }
        } catch (SQLException e) {
            throw new DbException(e);
        }
    }
private Connection getConnection() {
        JdbcTransaction tx = transationHandler.get();
        try {
            if (tx == null) {
                return dataSource.getConnection();
            } else {
                return tx.getConnection();
            }
        } catch (SQLException e) {
            throw new DbException(e);
        }
    }
获取一个当前线程的连接(事务中)，如果没有，则新建一个。