Document the need for configuration files to have a file extension

[prabdeb]

Not reading properties for property file passed by -Dspring.config.location=<property file>, where <property file> does not have any extension.

Reproduce: Execute the the following example command -

java -Dspring.config.location=/mount/application-secret-property -jar /home/user/application.war

Where /mount/application-secret-property does not have any extension

Related discussions:

1. stackoverflow - spring-config-location-is-ignored
2. Related code in spring boot
3. Some more discussion on use case

[wilkinsona]

Thanks for the report. This is working as designed so I think we should update the documentation. We should note that a file extension is required to identify which loader should handle the file. This applies both to a location that points to an individual file and to the files in a directory that is specified as the config location.

[wilkinsona]

Actually, let's do two things. In addition to updating the documentation which we can do now, we can also consider adding support for loading configuration from files with no extension so that you don't have to rename the file to get it to work. I've opened #22280 to track that.