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
I had the same issue. I'm using OS X Yosemite and initially had installed R through homebrew
I performed the following steps to fix it:
sudo R CMD javareconf
Opened up R from my terminal and ran:
install_packages("rJava")
install_packages("xlsx")