Its being a real nightmare to install rjava on my Mac.
My setup:
MacOS 10.9.5 Java: 7u71 (64 bits dowloaded from Oracle site) R: R version 3.1.1 (201
This worked for me:
sudo R CMD javareconf
Then, in the R interpretor:
install.packages('rJava', type='source') install.packages('xlsx', type='source')