1. Make a Java class and package it into a JAR:

IzPack can execute Java classes provided by third party developers.  

This can be useful to extend IzPack's functionality in a number of ways

Some examples:

• to control the writing of configuration files during installation or
• creating a custom log.  

IzPack can display output from these classes via a ProcessPanel, or you could create a custom (possibly hidden) panel that calls your Java code.  

This following example shows how to use a custom Java class with a ProcessPanel.

An external Java class must have a run() method with some parameters.

Note: This is not (NOT!) the run() method from the java.lang.Runnable interface. Nor is this codified as an interface in the IzPack javadoc.  Instead, this would seem to be a magic method signature that is otherwise undocumented.

a. Contents of a minimal file that matches the requirements:

This class uses the com.izforge.izpack.util.AbstractUIProcessHandler class to log output into a calling ProcessPanel. See the IzPack javadoc for details.

b.  Compile your Java class

You will obviously need to include the standalone-compiler.jar on your classpath, in order to compile your class:

c. Package your Java class into a separate JAR

IzPack can only reference JAR files not individual class files from a ProcessPanel.

NB: You should eventually use Maven to automate the compilation, packaging and moving of your JAR file.

2. Set up the install.xml file

a. Add <resources> entry.

In the <resources> section of your install.xml, reference an external file called "ProcessPanel.Spec.xml".

The ProcessPanel.Spec.xml file holds the XML configuration for the external Java class you want to execute.

b.  Reference your JAR

In the install.xml file's top level, reference the JAR file containing your class.

This is partially documented at:
http://izpack.org/documentation/installation-files.html#the-jar-merging-element-jar

NB: The path to the JAR is the path at *compile time*.

A good place to put this is near the <resources> definition.

c.  Use a ProcessPanel to execute your Java class

In the install.xml file in the panels section, use a ProcessPanel to execute your Java class.

3. Create the ProcessPanel.Spec.xml file

This is partially documented in  http://izpack.org/documentation/panels.html#processpanel

IzPack javadoc

The IzPack javadoc is available in the distribution (although apparently not online). There is an RPM for Linux users.