Actually, its pretty straight forward. Jar in a Jar isnt a thing but combining jars is. Jars are just zip files so you can unzip and rezip to create an Uber (or Fat) Jar.
Example below of a JDBC jar I created that combines all the dependencies. You'd need to do this after you ran SLC.
Been a while but from memory I did run into issues with B4J and the things in the root of the Jar (eg LICENSE, NOTICE etc) this is why they get deleted.
Also, I did try some 3rd party tools (google jar combiner) to do this but found they didn't tidy up these things which caused downstream issues - there's likely a post on the forum somewhere.
@echo off
cd /d %0\..
SET Lib_Name=iotdb-jdbc-0.12.2-all-deps.jar
rmdir /S /Q all
del /Q %Lib_Name%
mkdir all
for %%f in (.\libs\*.jar) do (
echo %%f
C:\Apps\7-zip\7z.exe x %%f -oall -r -aoa -y
)
del /Q .\all\*.class
del /Q .\all\*.html
del /Q .\all\LICENSE
del /Q .\all\NOTICE
rmdir /S /Q .\all\META-INF
C:\Apps\7-Zip\7z a %Lib_Name% .\all\*
copy %Lib_Name% C:\Apps\B4J\AdditionalLibraries\%Lib_Name%
pause