Extend spring-boot-maven-plugin to allow customizing the loader for java SPIs

[MFAshby]

I want to install a custom DateFormatSymbolsProvider to work around this issue where short month symbols changed in the JVM default locales. The supported mechanism for doing this is to use an SPI, which requires adding a file to my executable WAR: META-INF/services/java.text.spi.DateFormatSymbolsProvider. This must be in the root of the WAR, which is where the loader lives, not my application code.

I am using spring-boot-maven-plugin to create my executable WAR, and I cannot find any supported mechanism for customizing the loader in this way. There are workarounds such as using antrun to post-process the executable WAR, but these introduce extra complexity in the build and are not easily supported to also work in the IDE.

I think this relates to #6626 but I can't tell if it's an exact duplicate. Java SPIs are a well defined way of customizing JVM components and it seems unusual there's no documented way to use them in a spring boot application.

[wilkinsona]

Yes, this is a duplicate of #6626.