warning: jni.h: No such file or directory

Problem:

Layer_Connections.h:2:17: warning: jni.h: No such file or directory
In file included from Layer_Connections.cpp:4:
Layer_Connections.h:15: error: ‘JNIEXPORT’ does not name a type

Solution:
jni.h is part of standard java distribution. Either you don't have java openjdk installed, or your include path is wrong. This is what worked for me :

cd /usr/lib/jvm
sudo ln -s java-1.6.0-openjdk-1.6.0.0.x86_64/ java-1.6.0-openjdk-1.6.0.0
sudo ln -s java-1.7.0-openjdk-1.7.0.9.x86_64/ java-1.7.0-openjdk-1.7.0.9