How to pass heroku config var to spring boot's application.properties?

Question

I'm trying to pass custom heroku config variable into application.properties but no value is passed.

My application.properties entry:

spring.mail.username=${SPRING_MAIL_SENDER_USERNAME}

Then I inject this value into String variable:

@Value("${spring.mail.username}")
private String SENDER_MAIL_USERNAME;

but the SENDER_MAIL_USERNAME is an empty string when I try to use it.

I can get the proper value like this:

System.getenv("SPRING_MAIL_SENDER_USERNAME");

but this is not what I'm looking for. Anyone knows what I'm doing wrong here?

EDIT:

Maybe it's worth to add that my project uses maven with 2 modules (backend and frontend). Simplified project structure looks like this:

-app  
  -backend  
    -src.main  
      -java.com.jakubeeee.app  
        -some java files...  
      -resources  
        -application.properties  
  -frontend  
    -src   
      -some web files...  

I also use Procfile that contains:

web: java -Dserver.port=$PORT -jar $PATH_TO_JAR

where $PATH_TO_JAR is heroku config variable with value:

backend/target/myjarname.jar

Answer 1

What you show here should work. Double check spelling, etc. Otherwise, you can pass the option in the Procfile as a Java property like this:

web: java -Dspring.mail.username=${SPRING_MAIL_SENDER_USERNAME} -jar target/myapp.jar

Also be sure to confirm that it works with a hardcoded value like spring.mail.username=foo (otherwise you'll know it's something other than the env).

EDIT:

I realize now that you're using a .properties file and not a .yml file. I'm unsure if env vars are supported in Spring's application.properties. You might want to try application.yml config instead.