title: Spring Boot - nesting ConfigurationProperties
body: <p>Spring boot comes with many cool features. My favourite one is a type-safe configuration mechanism through <a href="http://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#boot-features-external-config-typesafe-configuration-properties"><code>@ConfigurationProperties</code></a> 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 <code>Cluster</code> and <code>Session</code> 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:</p>
  
  <pre><code>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
  </code></pre>
  
  <p>(this snippet comes from <a href="http://symfony.com/doc/current/cookbook/doctrine/multiple_entity_managers.html">Symfony documentation</a>)</p>
  
  <p>Is it possible in spring-boot using ConfigurationProperties? Should I nest them?</p>