Gephi开源学习-API与SPI之困惑

今天再次开始学习Gephi，导到netbeans中看到API和SPI两个包，google如下：

What is the difference between Service Provider Interface (SPI) and Application Programming Interface (API)?
More specifically, for Java libraries, what makes them an API and/or SPI?
the API is the description of classes/interfaces/methods/... that you call and use to achieve a goal
the SPI is the description of classes/interfaces/methods/... that you extend and implement to achieve a goal
Put differently, the API tells you what a specific class/method does for you and the SPI tells you what you must do to conform.
Sometimes SPI and API overlap. For example in JDBC the Driver class is part of the SPI: If you simply want to use JDBC, you don't need to use it directly, but everyone who implements a JDBC driver must implement that class.
The Connection interface on the other hand is both SPI and API: You use it routinely when you use a JDBC driver and it needs to be implemented by the developer of the JDBC driver。

理解为：

        1.API是为实现某一目标，供程序员调用或使用的一种接口/类/方法......

        2.SPI是为实现某一目标，程序员必须继承或者是实现的接口/类/方法......

附详细解析：http://www.cnblogs.com/happyframework/p/3325560.html