Can Key value pairs in application.properties be considered as environmental variables?

Question

New to spring boot.

While exploring spring boot env variables, came to know that, env variables can be accessed by ${KeyName} from code.

Got a question like,

Case 1: In @Configuration files, we are accessing keys in application.properties using @Value(value = "${KeyName}"). So, we are using almost same syntax for accessing env variables and accessing keys in application.properties.

Case 2: When trying to access the keys in application.properties using system.getEnv("keyname"), I got only null.

Case 3: Recently worked on configmap in kubernetes with spring boot.

Config file looks like,

spec:
  containers:
  - name: demo-configconsumercontainer
    image: springbootappimage:latest
    ports:
    - containerPort: 8080
    envFrom:
      - configMapRef:
          name: example-configmap

All the values from configMap is exported as environmental variables and I am accessing those values by @Value(value = "${KeyName}") and by system.getEnv(KeyName).

1. My question is, how case 3 is working when case 2 is not.
2. Is Spring boot made such a way that, it is allowing to access by ${KeyName} and not by system.getEnv(KeyName)? (ie. Case 2)

Could some one clarify my questions here.

Answer 1

See the Spring docs:

https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-external-config.html

Spring includes environment variables as a potential property source, but does not export its properties defined in other ways as environment variables. So it isn't a two way street, which is why case #2 does not work.

Case #3 is a separate reality, just the fact that when K8s runs a container defined in this way with env vars, it makes those vars available in the container environment. Any software system or programming language able to read environment variables will be able to refer to those variables, including Java code. This has nothing to do specifically with Java or Spring...it's just another way to inject environment variables into the runtime environment.

UPDATE: I didn't see @ShaileshPratapwar's answer until I posted my own. Seems our answers are roughly the same, although I think it's good that you know where the list of property sources, and their order of priority, comes from. It's very clearly defined by the Spring docs.