Application configuration

In this section, you will:

  • Get to know the application.yml file.

  • Use the @ConfigurationProperties annotation.

  • Use profiles to simulate different application environments.

application.yml

We will start this example by adding an entry to the application.yml file. This YAML file holds all configuration values for a specific application.

Place the following snippet in the file.

applicationKey: 73RNNJIJFN83N3R3NKFNK

We are defining a configuration item with name applicationKey and value 73RNNJIJFN83N3R3NKFNK.

To use this configuration item, we can use the @Value annotation in our class. Modify the StartupLogger class to the one below:

A component which displays a configuration value!
@Component
@Slf4j
public class StartupLogger {

    @Value( "${applicationKey}" ) (1)
    private String applicationKey;

    @Bean
    public Void dummyBean() {
        LOG.info( "Your application key is: {}", applicationKey);
        return null;
    }
}
1 The @Value annotation can be used to perform expression based dependency injection. In combination with the property syntax or the Spring Expression Language (SpEL), it can be used to fetch properties from a configuration file or beans.

Run the application.

$ mvn spring-boot:run

In the console you should see the following:

INFO --- [ost-startStop-1] c.e.demo.application.StartupLogger       : Your application key is: 73RNNJIJFN83N3R3NKFNK

Next up, you will see how we can use @ConfigurationProperties. This is a more structured way of defining your configuration values.

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