How to use environment variables for Springboot application using a .env file?

Question

I am trying to build a Springboot application which connects to a DB. I would like to use a .env file which has the sensitive content. At the first hand, I am testing by changing the port to 8081. My .env file has the following content

PORT=8081

My application.properties has the following content

server.port=${PORT}

I have a run time error that PORT cannot be resolved, which is to be expected when I did not know how to feed the .env file to properties.

Could someone point me in the right direction?

PS: I am using the port as an example, if this succeeds I will also set the DB Credentials with the .env file.

UPDATE: I would prefer using .env file because when the application is deployed using AWS CodePipeline, I can have the environment variables set in the CodeBuild stage where I would be building the jar and eventually a docker image in this stage. Something like this.

EnvironmentVariables:
  - Name: PORT
    Value: "{resolve:secretsmanager:DBCredentials:SecretString:port}"

The error is Caused by java.lang.IllegalArgumentException: Could not resolve placeholder 'PORT' in value "${PORT}"

Answer 1

I think you have the react approach ! But in spring for using multiple environments, it's better to have a properties file or yaml by environment.

Ps: File name must be named like application-{environment name}.properties and must be in the resources folder.

For dev: File name : application-dev.properties

server.port=8089

For IT: File name : application-it.properties

server.port=8090

In the application.properties file, where usually we put some shared properties between all the environments, we can add the propertie : spring.profiles.active = dev // you can put what you want depending on your needs. If you have more than one profile you can separate them by " , ".

For more details you can check spring profiles