Installers can be debugged using remote debugging:
java -Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=5005 -jar installer.jar
The above specifies to suspend execution of the installer until the debugger attaches on port 5005.
NOTE: if the installer requires elevated privileges, it should be run as an administrator.
This is required as the installer relaunches itself if elevated permissions are needed.