[FIXED] Get properties by @Value and put it into application.yml programmatically. Java with SpringBoot

Issue

I use Azure KeyVault to store some values. I need to get this values (e.g. mysql-uri or client-secret) and create new properties in application.yml (and application-local.yml). First of all, I tried to create Configuration-class with @Bean like getDataSource to create connection to database and I did it successfully, but I need to add other fields as well, such as 'oauth.client.secret'.

So I tried to get values and create 'properties' in main-class, but @Value couldn't be static and this solution throws NPE. I tried to create new Configuration-class and get properties from it and then pull it into SpringApplicationBuilder, but I need ApplicationContext (so SpringApplication.run will be called) to get an instance (bean) of this class with values...

I don't know what to do next, I'm stuck. Ready to rewrite and show any solution you need.

UPDATE 1:

    @Value("${secret}")
    private String clientSecret;

    public static void main(String[] args) {
        new SpringApplicationBuilder(DefaultApplication.class).properties(getProperties()).run(args);        
    }

    @NotNull
    private static Properties getProperties() {
        Properties properties = new Properties();
        properties.put("oauth.client.secret", Objects.requireNonNull(clientSecret));

        return properties;
    }

clientSecret with error: Non-static field 'clientSecret' cannot be referenced from a static context.

Solution

You can try this way of injecting properties. This uses a simpler convenience class SpringApplication instead of SpringApplicationBuilder.

MainClass.java

@SpringBootApplication
public class MainClass {
    public static void main(String... args) {
        SpringApplication.run(MainClass.class, args);
    }
}

The application.yaml will be automatically loaded into the context by Spring Boot (unless you have configured against it). Properties can be reused, redefined (using profiles) and system/env variables can be used as well.

NOTE Spring configurations are pretty flexible and powerful. Please read this documentation https://docs.spring.io/spring-boot/docs/current/reference/html/features.html#features.external-config

application.yaml

app:
  name: Demo
oauth:
  client:
    secret: ${app.name} // This will have "Demo"
env:
  path: ${SOME_ENV_VAR} // This will take SOME_ENV_VAR from env variable

SomeService.java

@Service
public class SomeService {
    @Value("${app.name})
    private String appName;

    public void printAppName() {
        log.info(appName); // will log the appname
    }
}

Answered By - aksappy