How to access environment variables from .properties using java?

Question

I'm using java to implement AWS SQS. I want to have a.properties file in which I want to store and access an environment variable for an AWS SQS Access and Secret Key. At the moment, my.properties file is:

dev.access.key={$AWS_ACCESS_KEY}
dev.secret.access.key={$AWS_SECRET_ACCESS_KEY}

My code to access these variables is:

String awsAccessKey = properties.getProperty("dev.access.key");
String awsSecretAccessKey = properties.getProperty("dev.secret.access.key");

I have already instantiated properties and it's well defined. I'm able to get other properties but unable to access the environment variables Access and Secret Key, which I require. That is currently awsAccessKey, awsSecretAccessKey are defined as null. Is there perhaps something wrong with my syntax of how I'm accessing those environment variables?

Answer 1

This can be achieved with https://github.com/webcompere/lightweight-config

Your placeholder syntax would need to change slightly:

dev.access.key=${AWS_ACCESS_KEY}
dev.secret.access.key=${AWS_SECRET_ACCESS_KEY}

Then you'd write:

Properties myProps = ConfigLoader.loadPropertiesFromResource(
    myproperties.properties");

Lightweight Config also supports properties on filesystem, rather than on the classpath (as above) and allows you to use YML instead of the .properties syntax.

Answer 2

You can use org.apache.commons.text.StringSubstitutor

import java.util.Properties;
import org.apache.commons.text.StringSubstitutor;

public class EnvSubst {
    public static void main(String[] args) {
        // For the demo, create a Properties, normally you will read Properties from file
        Properties p = new Properties();
        p.put("tempfolder", "${TEMP}");

        System.out.println("path value : " + 
            new StringSubstitutor(System.getenv()).replace(p.get("tempfolder")));
    }
}