A fix for the Pi 2 came from richardghirst/rpi_ws281x. This project uses it (and another C library, see below) to drive the LEDs. You need to compile the C on the Pi and generate the shared objects (.so).
If you need to, use SWIG to generate the JNI bindings;
cd src/main/c/rpi-ws281x/
swig -java -package bad.robot.unicorn.neopixel.ws2811 rpi_ws281x.i
Follow these steps to build it.
cd src/main/c/rpi-ws281x/lib
make lib
That will create .o and .a files in the lib folder. Then use the Makefile one level up to compile the Java wrapper and create the .so file (this actually calls into the lib/Makefile so that's why the previous step is optional).
cd src/main/c/rpi-ws281x/
make build
Look for the generated .so file and remove any .o files.
The library uses ws2812 as the underlying driver. It's a C library from 626Pilot/RaspberryPi-NeoPixel-WS2812, although I've taken the modified version from pimoroni/unicorn-hat
Use SWIG to generate the JNI bindings (manually targeting the Pi 2 only);
cd src/main/c/ws2812/lib
swig -java -package bad.robot.unicorn.neopixel.ws2812 ws2812-RPi.i
Compile the .o files.
gcc -fPIC -c ws2812-RPi.c ws2812-RPi_wrap.c -DPERI_BASE=0x3F000000 -DRPI2 -I/usr/lib/jvm/jdk-8-oracle-arm-vfp-hflt/include -I/usr/lib/jvm/jdk-8-oracle-arm-vfp-hflt/include/linux
Compile the shared object.
gcc -shared ws2812-RPi.o ws2812-RPi_wrap.o -o libws2812-RPi.so
or do it all via the src/main/c/ws2812/lib/Makefile (which will also build the Pi B+ version rather than the just the Pi 2 version).
cd src/main/c/ws2812/lib
make swig_prep
make shared
Setting the LD_LIBRARY_PATH in the pom means you should be able to run the hardware tests directly with mvn failsafe:integration-tests and blinky lights will blink on the physical HAT. You need to run sudo mvn though.
<environmentVariables>
<LD_LIBRARY_PATH>${project.basedir}/src/main/c/ws2812</LD_LIBRARY_PATH>
</environmentVariables>
As a reminder to myself; Environment variables are OS settings available via System.getenv(). For example, set using export FOO=xxx for example. System properties are set using -D on the command line and are available via System.getProperties(). For example, java.library.path. They can be set at runtime using System.setProperty.
Running from the shell, something like this should work.
sudo java -cp target/test-classes:target/classes/ -Djava.library.path=/home/pi/dev/unicorn-hat-java/src/main/c/ws2812 bad.robot.unicorn.integration.BasicIntegrationTest
If you see an error like this,
Exception in thread "main" java.lang.UnsatisfiedLinkError: no ws2812-RPi in java.library.path