For some reason, I could not install the rJava package without root privilege (using sudo R and then install.packages('rJava')). It should have solved my problem, however I can only use this package when launching R with sudo R. If I launch it without sudo, R will act as if this package is not installed.
I tried looking at /usr/local/lib/R/site-library, every package belongs to my user and group "staff" except this one, that belongs to root and staff. The rights for every package are rwxrwxr-x and I am in group staff, so I should have all the permissions I need. In addition, I tried changing the owner of the rJava folder to my user and it didn't change anything. Do anybody have any idea why rJava is not recognized if I start R without sudo? Thanks!