Spring Boot - nesting ConfigurationProperties

Question

Spring boot comes with many cool features. My favourite one is a type-safe configuration mechanism through @ConfigurationProperties and corresponding yml/properties files. I'm writing a library that configures Cassandra connection via Datastax Java driver. I want to allow developers to configure Cluster and Session objects by simply editing yml file. This is easy in spring-boot. But I want to allow her/him configure multiple connections this way. In PHP framework - Symfony it is as easy as:

doctrine:
  dbal:
    default_connection: default
    connections:
      default:
        driver:   "%database_driver%"
        host:     "%database_host%"
        port:     "%database_port%"
        dbname:   "%database_name%"
        user:     "%database_user%"
        password: "%database_password%"
        charset:  UTF8
      customer:
        driver:   "%database_driver2%"
        host:     "%database_host2%"
        port:     "%database_port2%"
        dbname:   "%database_name2%"
        user:     "%database_user2%"
        password: "%database_password2%"
        charset:  UTF8

(this snippet comes from Symfony documentation)

Is it possible in spring-boot using ConfigurationProperties? Should I nest them?

Answer 1

You could actually use type-safe nested ConfigurationProperties.

@ConfigurationProperties
public class DatabaseProperties {

    private Connection primaryConnection;

    private Connection backupConnection;

    // getter, setter ...

    public static class Connection {

        private String host;

        // getter, setter ...

    }

}

Now you can set the property primaryConnection.host.

If you don't want to use inner classes then you can annotate the fields with @NestedConfigurationProperty.

@ConfigurationProperties
public class DatabaseProperties {

    @NestedConfigurationProperty
    private Connection primaryConnection; // Connection is defined somewhere else

    @NestedConfigurationProperty
    private Connection backupConnection;

    // getter, setter ...

}

See also the Reference Guide and Configuration Binding Docs.