Support .env file for configuration properties

[linux-china]

Lots of developers use .env to process own configuration for script or app. Now I add spring.config.import in application.properties as following:

spring.config.import=optional:file:.env

and SpringBoot app throws the following exception:

Caused by: java.lang.IllegalStateException: File extension is not known to any PropertySourceLoader. If the location is meant to reference a directory, it must end in '/'
	at org.springframework.boot.context.config.StandardConfigDataLocationResolver.getReferencesForFile(StandardConfigDataLocationResolver.java:199)
	at org.springframework.boot.context.config.StandardConfigDataLocationResolver.getReferences(StandardConfigDataLocationResolver.java:121)

I think .env file could be considered as properties file for spring.config.import .

[scottfrederick]

@linux-china Thanks for getting in touch. Simply considering a .env file as a properties file wouldn't do what I think most users expect.

When Spring Boot reads key/value pairs from the system environment, additional processing is required to map the typical UPPERCASE_WITH_UNDERSCORES style of environment variable keys to the canonical form of Spring Boot property keys. This mapping is not done when configuration is read directly from a properties file. I suspect most users would use the environment variable style of keys in a .env file, so the fact that the key name mapping is not performed when importing the file as a properties file would result in the expected properties not being present in the Spring Environment.

In order for this to work as expected, a .env file would need to be recognized as a file containing key/value pairs similar to system environment variables, and processed accordingly. This is, of course, a bigger change than what you've suggested.

Can you elaborate on the types of properties that you would find convenient to set in a .env file instead of a local application.properties file?

[linux-china]

@scottfrederick Now I use jbang to write some scripts for Spring Boot App, scripts and app share some same configuration, such as database url etc, and https://github.com/cdimascio/dotenv-java is very friendly for jbang and kscript. I also have some script managed by just command runner, and .env is also supported by oh-my-zsh dotenv plugin, and .env variables will be loaded into env variables automatically for some command line tools. I mean .env is convenient for developers.

But now still ok for me, I can use ln -s .env env.properties and spring.config.import=file:env.properties also works well. Or ln -s .env application.properties for a local application.properties for Spring Boot.

[scottfrederick]

@linux-china Here's a more concrete example of what I think would be the problem with loading a .env file as a properties file:

In a properties file, you can set a property like spring.application.name=myapp. If you want to set this property as an environment variable, you can set SPRING_APPLICATION_NAME=myapp. Either property will resolve to spring.application.name in the Spring Environment (e.g. using @Value(${spring.application.name})).

If you have SPRING_APPLICATION_NAME=myapp in a properties file, this will not be resolved to spring.application.name because the property key mapping logic is not applied when reading properties files. Properties file are expected to use the canonical form.

Since .env files typically contain keys that conform to the environment variable naming conventions, I think users would naturally set properties like SPRING_APPLICATION_NAME=myapp in the .env file and then be surprised when the application name wasn't set as expected (because the file is being read as a properties file and the property key mapping isn't done). This will work if you set spring.application.name=myapp in the .env file, but you'd have to understand how Spring Boot works to know to use that form.

I can use ln -s .env env.properties and spring.config.import=file:env.properties

In your use case, are you using the canonical form in .env, or how are you setting the properties there?

[linux-china]

yes, I use normal key style form in .env file, and my .env file content as following:

nick=linux_china
management.server.port=9999

then I create link for .env with ln -s .env env.properties

my application.properties as following:

spring.application.name=spring-boot24-demo
spring.config.import=optional:file:env.properties

All work well, @Value("${nick}") private String nick; and management listen port is 9999

but one problem is the env variable, management.server.port could not be used as env variable name, and you have described this problem. Maybe I should do some modification for dotenv plugin, and convert management.server.port to MANAGEMENT_SERVER_PORT automatically.