Support for variables expansion in the @Key annotation

[lviggiano]

Example:

<servers>
    <dev> <!-- development environment -->
        <name>DEV</name>
        <hostname>devhost</hostname>
        <port>6000</port>
        <user>myuser1</user>
        <password>mypass1</password>
    </dev>
    <uat> <!--- user acceptance test environment -->
        <name>UAT</name>
        <hostname>uathost</hostname>
        <port>60020</port>
        <user>myuser2</user>
        <password>mypass2</password>
    </uat>
</servers>

Mapping class and example usage:

@Sources("classpath:org/aeonbits/owner/variableexpansion/KeyExpansionExample.xml")
public interface ExpandsFromAnotherKey extends Config {

    @DefaultValue("dev")
    String env();

    @Key("servers.${env}.name")
    String name();

    @Key("servers.${env}.hostname")
    String hostname();

    @Key("servers.${env}.port")
    Integer port();

    @Key("servers.${env}.user")
    String user();

    @DisableFeature(VARIABLE_EXPANSION)
    @Key("servers.${env}.password")
    String password();
}

@Test
public void testKeyExpansionFromAnotherKey() {
    ExpandsFromAnotherKey cfg = ConfigFactory.create(ExpandsFromAnotherKey.class);

    assertEquals("DEV", cfg.name());
    assertEquals("devhost", cfg.hostname());
    assertEquals(new Integer(6000), cfg.port());
    assertEquals("myuser1", cfg.user());
    assertNull(cfg.password()); // expansion is disabled on method level
}

@Test
public void testKeyExpansionFromAnotherKeyWithImportOverriding() {
    ExpandsFromAnotherKey cfg = ConfigFactory.create(ExpandsFromAnotherKey.class, map("env", "uat"));

    assertEquals("UAT", cfg.name());
    assertEquals("uathost", cfg.hostname());
    assertEquals(new Integer(60020), cfg.port());
    assertEquals("myuser2", cfg.user());
    assertNull("mypass2", cfg.password()); // expansion is disabled on method level
}

This way you can select ${env} in the ConfigFactory (or from the system properties) and have the above interface map to the appropriate section.

See: #56 #48

[lviggiano]

Implemented few days ago, missing the docs still, before to close this task.