About PL/Java packaging

The pljava-packaging subproject builds a single jar file that contains the files (including the API, implementation, and examples jar files, native code shared object, and PostgreSQL extension control files) that must be unpacked into a PostgreSQL installation so PL/Java can be used. These files could have been wrapped in a tar or zip format instead, but any site where PL/Java will be used necessarily has Java installed, and therefore support for the jar format, so it is an obvious choice.

The resulting jar can be simply extracted using the jar tool, and the files moved to the proper locations, or it can be run with java -jar. It contains two extra .class files to give it a very simple self-extracting behavior: it will run pg_config to learn where PostgreSQL is installed, and extract PL/Java’s files into the correct locations. See Installing PL/Java for the details.

If the file is simply extracted using the jar tool, those two added class files will also be extracted, and can be deleted; they are not needed for PL/Java’s operation.

Use with jshell as a testing environment

The added classes supply some additional methods, unused during a simple installation with java -jar, but accessible from Java’s JShell scripting tool if it is launched with this jar on its classpath. That allows jshell to serve as an environment for scripting tests of PL/Java in a running PostgreSQL instance, with capabilities similar to (and modeled on) the PostgresNode Perl module distributed with PostgreSQL.

See the javadoc for the Node class for details.