The jar can be used in the following ways:
When added to the classpath of the feature launcher it will unzip extensions according to a framework property (see below).
When installed as a bundle into sling, it will act as a extension to the OSGi installer and handle zip files that get installed as well as extensions in feature models that get installed (both, again, according to a framework property).
When invoked on the commandline, there is a converter main class that can be used to wrap a list of urls into a feature with an extension.
It looks like this:
java -cp ${HOME}/.m2/repository/org/apache/sling/org.apache.sling.commons.johnzon/1.2.2/org.apache.sling.commons.johnzon-1.2.2.jar:${HOME}/.m2/repository/org/apache/sling/org.apache.sling.feature/1.2.6/org.apache.sling.feature-1.2.6.jar:target/org.apache.sling.feature.extension.unpack-0.1.0-SNAPSHOT.jar \
org.apache.sling.feature.extension.unpack.impl.converter.Converter \
<mvn-id-of-resulting-feature> \
<name-of-extension-in-feature> \
<path-to-resulting-feature-file> \
<path-to-mvn-repository-to-store-artifacts> \
key=<optional-key-for-manifest> \
value=<optional-valure-for-manifest>\
<space separated list of urls>
Alternatively, there is an assembly provided.
The framework property org.apache.sling.feature.unpack.extensions can be used to give an OSGi header clause configuring which extensions to unzip, to which dir, and with what required manifest header.
It looks like this:
-Dorg.apache.sling.feature.unpack.extensions=<extension-name>;dir:=<path-to-dir-on-disc>;default:=<[true|false]>;key:=<optional-key-in-manifest>;value:=<optional-value-for-key-in-manifest>;index:=<path-header-in-manifest><[,<clause>]*>