You can't reuse your JNIenv, cause it's specific to the function that created it (it's thread, scope and all). For getting a valid JNIenv for calling an java method from your callback you have to use JNI_GetCreatedJavaVMs() and AttachCurrentThread().
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.