https://docs.spring.io/spring-boot/docs/current/reference/html/executable-jar.html#executable-jar-property-launcher-features
loader.debug
loader.path
    coma-separated-list of additional cp entries
loader.system
loader.properties
    loader.system=true
    loader.path=build/libs/shared
    java.library.path=build/libs/shared

https://github.com/spring-projects/spring-boot/tree/master/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader

PropertiesLauncher:
https://docs.spring.io/spring-boot/docs/current/api/org/springframework/boot/loader/PropertiesLauncher.html
https://docs.spring.io/spring-boot/docs/current/reference/html/executable-jar.html#appendix.executable-jar.property-launcher
https://github.com/spring-projects/spring-boot/blob/master/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/PropertiesLauncher.java
https://github.com/spring-projects/spring-boot/blob/master/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/LaunchedURLClassLoader.java
https://github.com/spring-projects/spring-boot/blob/master/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/Handler.java
https://docs.spring.io/spring-boot/docs/2.0.0.M1/gradle-plugin/reference/html/#packaging-executable-configuring-properties-launcher

org/springframework/boot/loader
    ...
    JarLauncher.class
    ...

https://stackoverflow.com/questions/15930782/call-java-jar-myfile-jar-with-additional-classpath-option

BOOT-INF
    classes
        user-stuff-classes
    lib
        -//-

META-INF/MANIFEST.MF

Manifest-Version: 1.0
Start-Class: com.clarabridge.fxservice.App
Spring-Boot-Classes: BOOT-INF/classes/
Spring-Boot-Lib: BOOT-INF/lib/
Spring-Boot-Version: 1.5.8.RELEASE
Main-Class: org.springframework.boot.loader.JarLauncher

gradle-plugin-ref:
https://docs.spring.io/spring-boot/docs/current/reference/html/build-tool-plugins-gradle-plugin.html

custom-layout-factory:
https://github.com/malcolmp6/CustomLayout1/blob/master/build.gradle