A JVM (Java Virtual Machine) running alongside PostgreSQL.

This is not production ready, just a proof of concept.

It only works on Linux, but it should be possible to run it on other OSes (feel free to create a PR).

You need to compile first the Java part, as the generated Jar file will be included as part of the extension. This is a standard Maven program:

cd java
mvn package

A jar file should have been generated under java/target/pgj-<VERSION>.jar.

You need a suitable JDK (version 6 or above) and export its path via the JAVA_HOME environment variable.

export JAVA_HOME=/path/to/jdk
cd pgxs
make
sudo make install

You need to make the JVM library (typically called libjvm.so) available in the LIBRARY_PATH, like:

sudo ln -s /usr/lib/jvm/java-8-oracle/jre/lib/amd64/server/libjvm.so /usr/lib

Add the library to postgresql.conf's shared_preload_libraries:

shared_preload_libraries = '... other libraries if any... , pgj'		# (change requires restart)

And restart PostgreSQL.