JBP_CONFIG_JAVA_MAIN java_main_class and arguments not supported

[stokpop]

The Go buildpack ignores java_main_class and arguments from JBP_CONFIG_JAVA_MAIN.

java_main_class

JBP_CONFIG_JAVA_MAIN: '{java_main_class: org.springframework.boot.loader.launch.PropertiesLauncher}'

Should override the manifest Main-Class and switch to classpath mode (-cp). Currently has no effect.

arguments

JBP_CONFIG_JAVA_MAIN: '{arguments: "--custom.arg=value"}'

Should append arguments after the main class. Currently has no effect.

Both are supported in the Ruby buildpack via config/java_main.yml.

[stokpop]

Additional fix added in this PR: when java_main_class is set, the registry now short-circuits before the normal container detection order, so it correctly overrides higher-priority containers like Spring Boot.

Previously, a Spring Boot app would be detected as Spring Boot before JavaMainContainer.Detect() was ever called, so JBP_CONFIG_JAVA_MAIN had no effect even with the initial fix.

Also added Ruby parity: when java_main_class is one of the Spring Boot launchers (JarLauncher, PropertiesLauncher, WarLauncher), SERVER_PORT=$PORT is now written to profile.d — matching the Ruby buildpack behaviour.

Example:

JBP_CONFIG_JAVA_MAIN: '{java_main_class: "org.springframework.boot.loader.launch.PropertiesLauncher", arguments: "--loader.home=/home/vcap/data"}'

Branch: issue-1267-fix-jbp-config-java-main (stokpop fork)