Google AppEngine: What is SystemServiceServlet and its relation to the _ah directory?

Question

Similar to this question, I'm interested in what this SystemServiceServlet even is, and what it's relationship is to the /_ah/spi/ directory I see in the autogenerated web.xml.

What purpose do these serve? Why/when are the necessary? Thanks in advance!

Answer 1

Behind the scenes each request to an Endpoint (a path in /_ah/api) is mapped to a request in the Endpoints Service Provider Interface (a path in /_ah/spi). The servlet SystemServiceServlet handles these requests. Without this mapping, requests to Endpoints will not succeed.

The Google Plugin for Eclipse adds the mapping automatically when you indicate that you wish to use Endpoints within your app. If you don't use GPE, you need to add the mapping manually.

Answer 2

I think this is related to the Google Endpoints API. I enabled them on my project and saw this same change right after.