public Connection getConnection() throws SQLException {
        Connection conn;
        if (username != null)
            conn = DriverManager.getConnection(jdbcUrl, username, password);
        else
            conn = DriverManager.getConnection(jdbcUrl);
        return conn;
    }
public Connection getConnection() throws SQLException {
        Connection conn;
        if (username != null)
            conn = DriverManager.getConnection(jdbcUrl, username, password);
        else
            conn = DriverManager.getConnection(jdbcUrl);
        return conn;
    }
public Connection getConnection ( ) throws SQLException { Connection conn ; if ( username != null ) conn = DriverManager . getConnection ( jdbcUrl , username , password ) ; else conn = DriverManager . getConnection ( jdbcUrl ) ; return conn ; }
这是唯一会被NutDao调用的方法
这是唯一会被NutDao调用的方法