The Pi4J Project now includes support for BPI-M1 and BPI-M1+,also can use it on BPI-R1.
This support has just been added and only cursory tests performed, so lets call it experimental for now, but I welcome you guys to try it out and let me know if you run into any trouble. You must use the Pi4J v1.1-SNAPSHOT builds until v1.1 gets released. You can manually download the JARs in ZIP or the installable .DEB package from this page:
Support includes Java programatic access and control of GPIO inputs/outputs, PWM, I2C, SPI, and UART (serial).
There is no documentation yet specifically for the Banana platforms, but apart from a few subtle differences in configuring a platform and pin/bus addressing, its basically the same. Perhaps better than documentation ... there are a number of examples (sample code) included in the build and available in the GitHub repo specific to each Banana platform: