Google Analytics is abbreviated as GA, and its functions are too powerful. Because of this, it takes a lot of time to research the GA API, and too many terms need to be sorted out.
The correct learning steps are:
First, find a privileged account and log in to GA (https://analytics.google.com/) to familiarize yourself with the interface functions.
Second, take a look at what GA has to offer with GA Help (https://support.google.com/analytics/#topic=3544906).
Finally, use the sample code provided on the official website to familiarize yourself with how to obtain GAAPI open data. (https://github.com/yaochuancun/google-api-java-client-samples)
I have been reading the API documentation for three days, but I still haven't done it. It is too energy-consuming.