What will be the best approach to read environment variables and JSON requests, responses

I have environment variables that need to be used in anywhere of the code. (And I can store theses environment variables in JSON format-if needed). Also, I have JSON requests and responses in separate JSON files which we used to validate in REST requests in my program. What will be the best approach to read config data and Use? Language: Java. Can Read conf data using Jackson or basic file reader...