Installing the R package xlsx requires rJava which, at least on linux,
can be difficult.

When attempting to install using 'install.packages('rJava')' it might prompt
the user to run 'sudo R CMD javareconf'. If during this the error 'jni.h not found'
occurs, rectify with the following procedure:

1.) Download openjdk7 using sudo apt-get install openjdk-7-*

2.) Locate the correct directory using 'locate jni.h'. If jni.h still not found,
locate and install an alternative Java library

3.) Ensure that the path to this library is made the java path by first running

sudo gedit /etc/environment

and the adding the line

JAVA_HOME="/usr/lib/<path>

where <path> is the location of the Java library include folder

i.e. if locate jni.h returns

/usr/lib/jvm/java-7-openjdk-amd64/include/jni.h

then the line to add to the environment file is

JAVA_HOME="/usr/lib/jvm/java-7-openjdk-amd64/"

4.) Re-run sudo R CMD javareconf and if no errors are thrown, continue with
installation of rJava through the R runtime environment.
