requested Java version ((null)) not available. Using Java at “” instead

If you are getting following errors while trying to install xlsx package in R (macOS)

> library(xlsx)
Loading required package: rJava
Error : .onLoad failed in loadNamespace() for 'rJava', details:

> library(xlsx)
JavaVM: requested Java version ((null)) not available. Using Java at "" instead.
JavaVM: Failed to load JVM: /bundle/Libraries/libserver.dylib
JavaVM FATAL: Failed to load the jvm library.
Error : .onLoad failed in loadNamespace() for 'xlsx', details:
  call: .jinit()
  error: JNI_GetCreatedJavaVMs returned -1

Error: package or namespace load failed for ‘xlsx’

try following

> sudo R CMD javareconf -n
> R
> install.packages('rJava', type='source')
> install.packages('xlsx')
> library(xlsx)

If you are looking for more JNI samples, take a look here: http://jnicookbook.owsiak.org