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kdb-mount-java.md

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kdb-mount-java(1) -- Mounting Java Plugins

SYNOPSIS

kdb mount-java [<path> <mount point>] [<plugin> [<config>] [..]]

All options except <plugin> are passed directly to kdb mount. For details on these options see kdb-mount(1).

The <plugin> arguments are preprocessed before they are passed to kdb mount. If a <plugin> argument starts with java:, it is interpreted as a fully-qualified Java class name. The script replaces these java:* arguments with the appropriate arguments for kdb mount (see below).

<plugin> arguments that start with kdb: or have no prefix, are passed to kdb mount as is (after removing the optional kdb: prefix). The kdb: prefix exists to avoid potential name collisions between a Java plugin and C plugin.

DESCRIPTION

This helper command exists, because (unlike a "normal" C plugin) mounting a Java plugin requires multiple arguments. This is because you actually need to mount the process plugin with the correct configuration for a Java plugin.

The following command mounts the C plugins dump and type together with the Java plugin org.libelektra.plugin.WhitelistPlugin with the file config.file at user:/tests/process:

sudo kdb mount-java config.file user:/tests/process kdb:dump java:org.libelektra.plugin.WhitelistPlugin type

This internally expands to (something like) this complicated snippet:

KDB_VERSION="$(kdb --version | sed -nE 's/KDB_VERSION: (.+)/\1/gp')"
sudo kdb mount config.file user:/tests/process dump process "executable=$(command -v java)" 'args=#3' 'args/#0=-cp' "args/#1=/usr/share/java/libelektra-$KDB_VERSION-all.jar:/usr/share/java/process-$KDB_VERSION.jar:/usr/share/java/whitelist-$KDB_VERSION.jar" 'args/#2=org.libelektra.process.PluginProcess' 'args/#3=org.libelektra.plugin.WhitelistPlugin' type

As you can see, every argument for a Java plugin is replaced by several arguments. Even worse, the arguments depend on how Elektra is installed on your system. The mount-java knows where Elektra's JARs are installed (/usr/share/java above) and constructs a classpath argument for the JVM. It also chooses the PluginProcess class as the main class and finally instructs this class to load the WhitelistPlugin.

However, mount-java isn't magic and it only works this smoothly for plugins that come bundled with Elektra. If you have external plugins, you must also specify the additional classpath for these plugins like this:

export CLASSPATH=/path/to/foo.jar:/path/to/bar.jar
sudo --preserve-env=CLASSPATH kdb mount-java config.file user:/tests/foobar java:org.example.Foo java:org.example.Bar java:org.libelektra.plugin.WhitelistPlugin

Here we added /path/to/foo.jar and /path/to/bar.jar to the classpath, so that the classes org.example.Foo and org.example.Bar can be found. We can still use org.libelektra.plugin.WhitelistPlugin, because Elektra's JARs are always added to the classpath.

SEE ALSO