Issues with installing ENMTools under newest versions of R

During the course I co-taught with Matt Fitzpatrick in Glasgow a few weeks ago, it came out that a number of people were having trouble installing ENMTools.  A lot of this seems to stem from the newest version of R, and in particular how it interacts with your Java installation.

Some Mac users (including me) were able to fix this just by going to the console and typing "R CMD javareconf" and restarting R.

Windows users seemed to have much more significant issues, however.  There seemed to be several issues, but here's a solution that helped several of the students, courtesy of Hirzi Luqman:

Error:
* installing *source* package ‘ENMTools’ ...
** R
** data
*** moving datasets to lazyload DB
** tests
** byte-compile and prepare package for lazy loading
Error : .onLoad failed in loadNamespace() for 'rJava', details:
  call: dyn.load(file, DLLpath = DLLpath, ...)
  error: unable to load shared object '/Library/Frameworks/R.framework/Versions/3.5/Resources/library/rJava/libs/rJava.so':
dlopen(/Library/Frameworks/R.framework/Versions/3.5/Resources/library/rJava/libs/rJava.so, 6): Library not loaded: /Library/Java/JavaVirtualMachines/jdk-9.jdk/Contents/Home/lib/server/libjvm.dylib
  Referenced from: /Library/Frameworks/R.framework/Versions/3.5/Resources/library/rJava/libs/rJava.so
  Reason: image not found
ERROR: lazy loading failed for package ‘ENMTools’
* removing ‘/Library/Frameworks/R.framework/Versions/3.5/Resources/library/ENMTools’
Installation failed: Command failed (1)


Problem:
ENMtools/rJava was looking for (and couldn't find) the library "libjvm.dylib" in the directory "/Library/Java/JavaVirtualMachines/jdk-9.jdk/Contents/Home/lib/server/", because no such directory existed (this refers to a Java 9 installation); I don't know why it looked for the file there...

Solution: I just copied the same file from the Java 8 directory (or whatever Java version is installed on the computer; in my case the directory was "/Library/Java/JavaVirtualMachines/jdk1.8.0_45.jdk/Contents/Home/lib/server/") to the R library directory "/Library/Frameworks/R.framework/Versions/3.5/Resources/lib/", and it worked


Update: GitHub user Sandy had a different issue, detailed here.  The fix in that case was:

I removed all PATH related to "java", then Add jvm.dll to PATH (adding "%JAVA_HOME%\jre\bin\server;" to PATH).
After that, I set up the JAVA_HOME in R:
Sys.setenv(JAVA_HOME="C:\\Program Files\\Java\\jdk1.8.0_171\\").