src/org/nutz/dao/impl/SimpleDataSource.java
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