Android :: Kernel / Userland Input Events Translation Process

I am now learning how android handles linux input events from kernel raw input events to the userland level KeyEvent and so on. And I want to handle input events in native language. I've do some experiments on handling events using NDK but the touch screen events are very hard to handle(when I touch the screen, It generates a lot of kernel events).

I've read the eventhub class in framework base dir in the android source repo. And I now I know how android collects linux kernel raw events using eventhub class by reading from /dev/input/event* , but I still have no idea how it translates these raw events into the userland logic input events like KeyEvent. The file keyinput service only wrappers eventhub to JNI functions but there are no translation. So please give me some hints on the kernel event and userland event translation process.