Spring Could not resolve placeholder when lower case environment variable is added

Affects: Spring 6.0.9

Due to an migration of our company application configurations we experience a rather strange issue when applying environement variables in different cases: In our setting we have two variables with nearly the same content but with slightly different names e.g. some_env_VARIABLE and some_env_variable. We are only trying to read one of these variables but in some cases our application fails to start.

Example application:

@SpringBootApplication
public class DemoApplication {

    @Value("${some_env_VARIABLE}")
    String value;

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

}

When started with environment some_env_VARIABLE=bla this application runs as expected.

When another environment variable is added some_env_VARIABLE=bla;some_env_variable=bla the application fails to start:

Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder 'some_env_VARIABLE' in value "${some_env_VARIABLE}"
    at org.springframework.util.PropertyPlaceholderHelper.parseStringValue(PropertyPlaceholderHelper.java:180) ~[spring-core-6.0.9.jar:6.0.9]

I could only reproduce this isse with environment variables. When using application properties the application still starts.

I've created a small sample application for reproduction issues: https://github.com/srcimon/spring-issue-duplicate-env

Comment From: srcimon

Sorry, not a Spring Framework issue. Actually a Windows / Java problem.