Difference between SPI and API?

Question

What is the difference between Service Provider Interface (SPI) and Application Programming Interface (API)?

More specifically, for Java libraries, what makes them a

Answer 1

API stands for Application Programming Interface, where API is a means for accessing a service / function provided by some kind of software or a platform.

SPI stands for Service Provider Interface, where SPI is way to inject, extend or alter the behavior for software or a platform.

API is normally target for clients to access a service and it has the following properties:

-->API is a programmatic way of accessing a service to achieve a certain behavior or output

-->From API evolution point of view, addition is no problem at all for clients

-->But API's once utilized by clients it can not (and should not) be altered / deleted unless there are an appropriate communications, since its a complete degradation of the client expectation

SPI on the other part are targeted for providers and has the following properties:

-->SPI is a way to extend / alter the behavior of a software or a platform (programmable vs. programmatic)

-->SPI evolution is different from API evolution, in SPI removal is not an issue

-->Addition of SPI interfaces will cause problems and may break existing implementations

For more explanation click here : Service Provider Interface