implemented variable expansion in @key annotation. See issue #63.

owner/src/main/java/org/aeonbits/owner/PropertiesInvocationHandler.java

@@ -76,7 +76,7 @@ private boolean equals(Method a, Method b) {
     }
 
     private Object resolveProperty(Method method, Object... args) {
-        String key = key(method);
+        String key = expandKey(method);
         String value = propertiesManager.getProperty(key);
         if (value == null)
             return null;
@@ -85,6 +85,13 @@ private Object resolveProperty(Method method, Object... args) {
         return result;
     }
 
+    private String expandKey(Method method) {
+        String key = key(method);
+        if (isFeatureDisabled(method, VARIABLE_EXPANSION))
+            return key;
+        return substitutor.replace(key);
+    }
+
     private String format(Method method, String format, Object... args) {
         if (isFeatureDisabled(method, PARAMETER_FORMATTING))
             return format;

owner/src/main/java/org/aeonbits/owner/util/EntryMap.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2013, Luigi R. Viggiano
+ * All rights reserved.
+ *
+ * This software is distributable under the BSD license.
+ * See the terms of the BSD license in the documentation provided with this software.
+ */
+
+package org.aeonbits.owner.util;
+
+import java.util.AbstractMap;
+import java.util.HashSet;
+import java.util.Set;
+
+import static java.util.Arrays.asList;
+import static java.util.Collections.unmodifiableSet;
+
+/**
+ * Utility class to create a Map from a single entry (key-value pair).
+ *
+ * <p>
+ * Example of usage:
+ * </p>
+ *
+ * <pre>
+ * import static org.aeonbits.owner.util.EntryMap.map;
+ *
+ * Map&lt;String, String&gt; myMap = map("foo", "bar");
+ *
+ * String bar = myMap.get("foo");
+ * </pre>
+ *
+ * @since 1.0.6
+ * @author Luigi R. Viggiano
+ */
+public class EntryMap<K, V> extends AbstractMap<K, V> {
+    private final Entry<K, V> entry;
+    private final Set<Entry<K, V>> entrySet;
+
+    private EntryMap(final K key, final V value) {
+        entry = new SimpleEntry<K, V>(key, value);
+        entrySet = unmodifiableSet(new HashSet<Entry<K, V>>(asList(entry)));
+    }
+
+    @Override
+    public Set<Entry<K, V>> entrySet() {
+        return entrySet;
+    }
+
+    public static <K, V> EntryMap<K, V> map(K key, V value) {
+        return new EntryMap<K, V>(key, value);
+    }
+}

owner/src/main/java/org/aeonbits/owner/util/package-info.java

@@ -0,0 +1,12 @@
+/*
+ * Copyright (c) 2013, Luigi R. Viggiano
+ * All rights reserved.
+ *
+ * This software is distributable under the BSD license.
+ * See the terms of the BSD license in the documentation provided with this software.
+ */
+
+/**
+ * Provides utility interfaces and classes.
+ */
+package org.aeonbits.owner.util;

owner/src/test/java/org/aeonbits/owner/variableexpansion/KeyExpansionTest.java

@@ -0,0 +1,134 @@
+/*
+ * Copyright (c) 2013, Luigi R. Viggiano
+ * All rights reserved.
+ *
+ * This software is distributable under the BSD license.
+ * See the terms of the BSD license in the documentation provided with this software.
+ */
+
+package org.aeonbits.owner.variableexpansion;
+
+import org.aeonbits.owner.Config;
+import org.aeonbits.owner.Config.DisableFeature;
+import org.aeonbits.owner.Config.Sources;
+import org.aeonbits.owner.ConfigFactory;
+import org.junit.Test;
+
+import static org.aeonbits.owner.Config.DisableableFeature.VARIABLE_EXPANSION;
+import static org.aeonbits.owner.util.EntryMap.map;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+
+/**
+ * @author Luigi R. Viggiano
+ */
+public class KeyExpansionTest {
+
+
+    @Sources("classpath:org/aeonbits/owner/variableexpansion/KeyExpansionExample.xml")
+    public interface MyConfig extends Config {
+        @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.${env}.password")
+        String password();
+    }
+
+    @Test
+    public void testKeyExpansion() {
+        MyConfig cfg = ConfigFactory.create(MyConfig.class, map("env", "dev"));
+
+        assertEquals("DEV", cfg.name());
+        assertEquals("devhost", cfg.hostname());
+        assertEquals(new Integer(6000), cfg.port());
+        assertEquals("myuser1", cfg.user());
+        assertNull(cfg.password()); // expansion is disabled on method level
+    }
+
+    @DisableFeature(VARIABLE_EXPANSION)
+    @Sources("classpath:org/aeonbits/owner/variableexpansion/KeyExpansionExample.xml")
+    public interface MyConfigWithExpansionDisabled extends Config {
+        @Key("servers.${env}.name")
+        String name();
+
+        @Key("servers.${env}.hostname")
+        String hostname();
+
+        @Key("servers.${env}.port")
+        Integer port();
+
+        @Key("servers.${env}.user")
+        String user();
+
+        @Key("servers.${env}.password")
+        String password();
+    }
+
+    @Test
+    public void testKeyExpansionDisabled() {
+        MyConfigWithExpansionDisabled cfg =
+                ConfigFactory.create(MyConfigWithExpansionDisabled.class, map("env", "dev"));
+
+        assertNull(cfg.name());
+        assertNull(cfg.hostname());
+        assertNull(cfg.port());
+        assertNull(cfg.user());
+        assertNull(cfg.password());
+    }
+
+    @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
+    }
+
+}

owner/src/test/resources/org/aeonbits/owner/variableexpansion/KeyExpansionExample.xml

@@ -0,0 +1,16 @@
+<servers>
+    <dev>
+        <name>DEV</name>
+        <hostname>devhost</hostname>
+        <port>6000</port>
+        <user>myuser1</user>
+        <password>mypass1</password>
+    </dev>
+    <uat>
+        <name>UAT</name>
+        <hostname>uathost</hostname>
+        <port>60020</port>
+        <user>myuser2</user>
+        <password>mypass2</password>
+    </uat>
+</servers>