Spring-boot application configuration

Question

I understand how to configure spring-boot and it provides a mature and sensible overriding mechanism that is documented well but I'm converting an application that gets its configuration from other source that is not in line with the spring-boot mechanism.

Ultimately the application makes properties available to the code that can be bound in using @Value("$the.prop.key:default") or used in spring xml config. The way that these properties are retrieved and bound cannot be changed.

I am trying to configure the embedded tomcat server port but the only way I can do this is using application.properties. I can change this to a different file and even change the location but I cannot change the mechanism (it has to be a file).

Looking into the spring-boot code I see it uses the notion of EmbeddedServletContainerCustomizer implementations to set these properties. Fine, I will create an implementation and set the server properties using this. But unfortunately you get 2 implementations trying to do the same thing ServerProperties and my implementation. The code orders these but because ServerProperties has not ordering it is set to the lowest priority and a low priority gets executed last and so my implementation gets overwritten.

Instead I have implemented a BeanPostProcessor:

@Named
public class SpringBootCustomConfigurator implements BeanPostProcessor {

@Value("$the.prop.key:8080")
private int port;

@Override
public Object postProcessBeforeInitialization(Object bean, String beanName)
        throws BeansException {
    if (bean instanceof ServerProperties) {
        ServerProperties serverProperties = (ServerProperties) bean;
        serverProperties.setPort(port);
    }
    return bean;
}
}

This does what I need to do but it isn't a satisfactory implementation. Any thoughts?

Answer 1

Given that it's about a new source of external properties, I think it would be more natural to write an ApplicationContextInitializer (or ApplicationListener to listen for one of the Spring Boot events on startup) that adds a new PropertySource to your Environment in the right place. You can register initalizers with the SpringApplication or using META-INF/spring.factories.