Immutable configuration of Spring boot

Question

I'm trying to find a way to use the Immutables library to create data classes for holding the configuration of my Spring Boot application.

My data configuration class is:

@Value.Immutable
@JsonDeserialize(as = ImmutableAuthConfig.class)
public interface AuthConfig {
    String domain();
    String clientId();

    @Value.Redacted
    String clientSecret();
}

While the main configuration class is set up as

@Configuration
@EnableConfigurationProperties
@ConfigurationProperties
public class Config {
    private ImmutableAuthConfig auth;

    public AuthConfig getAuth() {
        return auth;
    }

    public void setAuth(ImmutableAuthConfig auth) {
        this.auth = auth;
    }
}

I've tried some variations of using either ImmutableAuthConfig or just AuthConfig as a field, but nothing improved the situation. The configuration did not get picked up, and the auth field of the configuration remains null after application start-up.

Replacing the contents of the AuthConfig class with a traditional POJO solves the issue, but I would prefer an immutable object. Is there any way to convince Spring to interface with the classes generated by the Immutables library?

Answer 1

The library's support for modifiable classes supplies an approach that is pretty close to what I was searching for.

@Value.Modifiable
public interface AuthConfig {
    String domain();
    String clientId();

    @Value.Redacted
    String clientSecret();
}

This creates the class ModifiableAuthConfig which provides an interface satisfying Spring's JavaBeanBinder , which is used for deserializing the configuration.

It's furthermore necessary to supply an instance of the mutable AuthConfig class, which Spring can then populate:

@Configuration
@EnableConfigurationProperties
@ConfigurationProperties
public class Config {
    private ImmutableAuthConfig auth = ModifiableAuthConfig.create();

    public AuthConfig getAuth() {
        return auth;
    }
}

Any use of the loaded configuration can subsequently happen through the AuthConfig interface, which doesn't provide mutating methods.