Remove support for the deprecated layertools jar mode

[pfrollo]

This ticket is to request a documentation update.

I am aware of two approaches for creating Docker images for Spring Boot applications. Below are Dockerfile snippets.

# This approach generates and runs application classes stored in the `extracted_layers/application/BOOT-INF/classes/` folder. 
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RUN java -Djarmode=layertools -jar app.jar extract --destination extracted_layers
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ENTRYPOINT ["java", "-XX:+UseContainerSupport", "-XX:MaxRAMPercentage=75.0", "-XX:+UseG1GC", "org.springframework.boot.loader.launch.JarLauncher"]

# This approach generates and runs the application jar stored in the `extracted_layers/application/` folder
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RUN java -Djarmode=tools -jar app.jar extract --layers --destination extracted_layers
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ENTRYPOINT ["java", "-XX:+UseContainerSupport", "-XX:MaxRAMPercentage=75.0", "-XX:+UseG1GC", "-jar", "app.jar"]

Notice the difference in the tool used specified by -Djarmode .

The documentation mentions the jar approach: https://docs.spring.io/spring-boot/3.5/reference/packaging/container-images/dockerfiles.html

The documentation is missing mentioning the approach that generates and runs application classes using the -Djarmode=layertools options.
It would be beneficial to also document practical differences between the two different approaches.

[wilkinsona]

tools is the replacement for layertools with the latter being deprecated.

Ideally we would have removed layertools in 4.0 but missed the opportunity to do so. We can use this issue to track that overdue removal.

[Syed-2000]

Thanks for the clarification.

If help is welcome here, I’d be happy to contribute with:

• removing deprecated layertools support, or
• updating the documentation once the removal approach is finalized.

Please let me know if there’s a specific area where a contribution would be useful.