Reading a property before initialization of Spring Boot Application

Question

I have a situation where it would be useful to read a property from classpath:app.properties or classpath:presentation-api.properties for use prior to the spring application being run, in order to set a couple of legacy profiles.

So it would be something like this:

@SpringBootApplication
@PropertySource({"classpath:app.properties", "classpath:various_other.properties"})
public class MainApp extends SpringBootServletInitializer {

   @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {

        boolean legacyPropertyA = // might be set in classpath:app.properties or classpath:various_other.properties or not at all       
        boolean legacyPropertyB = // might be set in classpath:app.properties or classpath:various_other.properties or not at all

        if (legacyPropertyA) {
            builder.profiles("legacyProfileA");
        }
        if (legacyPropertyB) {
            builder.profiles("legacyProfileB");
        }

        return super.configure(builder);
    }
}

What's the cleanest way of retrieving legacyPropertyA and legacyPropertyB ?

Answer 1

I think you can combine @Value and @PostConstruct annotations in order to have a cleaner solution. Please, take a look in the example below:

@SpringBootApplication
@PropertySource({"classpath:application-one.properties", "classpath:application-two.properties"})
public class MyApplication extends SpringBootServletInitializer {

    @Value("${property.one}")
    private String propertyOne;

    @Value("${property.two}")
    private String propertyTwo;

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        return application.sources(MyApplication.class);
    }

    @PostConstruct
    public void initProperties() {
        System.out.println(propertyOne);
        System.out.println(propertyTwo);
    }
}

I hope this can help you. Please, let me know you have any questions.