If you want to use dependencies from another JAR, create a class path manifest entry in the shaded JAR.
<transformers>
<transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer" />
<transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
<mainClass>org.gkh.App</mainClass>
<manifestEntries>
<Class-Path>ojdbc8.jar</Class-Path>
</manifestEntries>
</transformer>
</transformers>The manifest is as follows.
Manifest-Version: 1.0
Built-By: gkh
Class-Path: ojdbc8.jar
Created-By: Apache Maven 3.6.2
Build-Jdk: 1.8.0_232
Main-Class: org.gkh.App