Spring Boot: Configuration Transforms

Coming from a .NET background, I was looking to emulate configuration transforms. I found some tutorials online but they weren’t totally complete. In this tutorial, we will be creating configuration files for a development tier and a production tier.

First create a new Spring Boot project. You will notice that an application.properties file was automatically created. For learning purposes, append the following:

test.constant=development_constant

Now create a new file in the same directory as your application.properties file named application-production.properties. Append the same key with the “production” value:

test.constant=production_constant

The next step is to create a way to inject these constants into our app. First create the interface:

public interface MyAppConfiguration {
      String getTestConstant();
}

Then create the implementation:

@Component
public class MyAppConfigurationImpl implements MyAppConfiguration {
    @Value("${test.constant}")
    private String testConstant;

    @Override
    public String getTestConstant() {
        return testConstant;
    }
}

We have everything setup to run the app in different configuration modes. After generating a fat jar, we can start the Spring Boot app in different configurations via the command line:

java -jar {jar_file_name}.jar # Run jar in development mode.
java -jar -Dspring.config.name=application-production {jar_file_name}.jar # Run jar in production mode. 
nohup java -jar -Dspring.config.name=application-production {jar_file_name}.jar & # Run jar in production mode in background. Requires linux. 

I am an Intellij user. Sometimes I want to start the application in a different configuration mode in Intellij. The easiest way to do this is to go to “Run > Edit Configurations > Override parameters”. In the “Name” column, enter “spring.config.name” and then enter the chosen configuration file name in the “Value” column. Here is a sample image which demonstrates this concept:

Evidently, it is incredibly easy to create different configurations per tier. This is not exactly how .NET configuration transforms work but it is close enough.