The Release Kit is configured to produce 'backwards compatible' Java
code using -target and -source.  When running 'javac' with these flags
this requires the "rt.jar" that matches the older JDK to be present --
not something that is shipped with newer JDKs.

The purpose of this directory is to store such rt.jar files, which are
then included into our compilation process through setting JAVACFLAGS
appropriate (using -bootclasspath).


At the time of writing Greenstone3 targets JDK 1.8 as the oldest
supported version.  Over time it is expected that we might start
accumulating other versions of rt.jar here, and so this file has been
named:

  rt-openjdk8.jar

which reflects that it is the OpenJDK Version 8 of rt.jar that has
been placed here. The actualy distribution of JDK used (OpenJDK)
should not be relevant here, but is reflected in the filename chosen
for reasons of transparency

For some additional background on compiling with -source and -target, see:

  https://stackoverflow.com/questions/15492948/javac-source-and-target-options

==

An added extra wrinkle is we also need to deal with any jar files in
jre/lib/ext (part of Java's extension mechanism) that are used by any
Greenstone3 Java source code.  It turns out Greenstone3 admin tool uses
javax.crypto package which means we also need to effectively add in
'jce.jar' here.  Unlike rt.jar, this is *not* something that is expected
to change over time, and forunately Oracle has a download for the extension:

  https://www.oracle.com/java/technologies/java-archive-downloads-java-plat-downloads.html#

At the time of writing, JCE-1.2.2

Following the instructions included in the download, there are in fact 4 jar files that
java/javac need access to to support the JCE extension:

  jce1_2_2.jar  local_policy.jar sunjce_provider.jar  US_export_policy.jar

These are provided there, and added in to the -bootclasspath part of JAVACFLAGS
through rk-setup.bash