How to consume properties from configmaps in Java Spring boot application deployed through Helm

Springboot can automatically infer variables from environment variables. In your application.properties or application.yaml, just use ${MY_ENVIRONMENT_VARIABLE:my-defaultvalue}.
Use helm to populate your configmap.Use configmap as environment variables into your deployment manifest.

This way you do not need to have multiple application.properties for dev, int ,prod inside your image. Keeping it intact across deployment.

And then in your helm chart, you can have multiple values.yaml example values-dev.yaml or values-int.yaml. you can also dynamically set helm values from command line, overriding the yaml file.

I have a demo app in github https://github.com/balchua/demo, which uses this pattern.

You could certainly use environment variables as Bal Chua suggests. If you do that you can override particular values at install time using --set or if you've a lot of config you can use the '-- values' flag and pass in a custom values.yaml file.

Another approach is to load a whole file using .Files.Glob (example in github) and load the file as part of the chart. You can then mount the file to /config to consume it in your spring boot application. Then your config file would be in the same form as a Spring boot config file, rather than a helm values.yaml. Though in many cases there needn't be much difference.

There's a discussion of how you could do similar for secrets (presumably you'll want to put your passwords in secrets) and use it for CI/CD in https://dzone.com/articles/hunting-treasure-with-kubernetes-configmaps-and-se (which is the article accompanying the github example). Basically you would use .Files.Glob with .AsSecrets instead of .AsConfig so as to encode the content. Many helm charts have the option to generate a random password if not specified but I'd guess you probably don't need that.

I'd recommend mounting the files (application.properties or application.yml) inside the ConfigMap onto somewhere on the file system that Spring Boot can automatically detect - then your app stays nice and simple