To run a Spring Boot 3 fat JAR with external libraries in a lib directory and configuration files in a config directory, follow these steps:

1. Directory Structure: Ensure your structure looks like this:

   enter image description here

2. Run the Application: Use the following command to start your application, ensuring to include the external libraries and configuration folder:

   java -cp "MyApp.jar:lib/*" org.springframework.boot.loader.WarLauncher --spring.config.additional-location=file:./config/

   Explanation:

   • -cp "MyApp.jar:lib/*": Sets the classpath to include your JAR and all JARs in the lib folder.

   • --spring.config.additional-location=file:./config/: Tells Spring to load configuration files from the config directory.

   Make sure to adjust the path separator if you're on Windows (; instead of :).