Getting kubernetes secret / env for authentication into java application
I am agree with @Kuikiker about getenv(). But one question why do u want to store credential in env variable. Unless u have some special need I believe you will be better off store them in your application.properties with encrypted value. I usually use jasypt encipher for that (https://www.baeldung.com/spring-boot-jasypt). Hope this helps.
System.getenv() is used to retrieve environment variable values; there is nothing wrong with it. However, since you are using SpringBoot you may find the following question valuable: Read environment variable in SpringBoot