Proposed feature: Property key from String field value

constretto-core/src/main/java/org/constretto/internal/DefaultConstrettoConfiguration.java

@@ -475,7 +475,7 @@ private <T> void injectFields(T objectToConfigure) {
                 try {
                     if (field.isAnnotationPresent(Configuration.class)) {
                         Configuration configurationAnnotation = field.getAnnotation(Configuration.class);
-                        String expression = "".equals(configurationAnnotation.value()) ? field.getName() : configurationAnnotation.value();
+                        String expression = getExpression(objectToConfigure, field, configurationAnnotation);
                         field.setAccessible(true);
                         Class<?> fieldType = field.getType();
                         if (hasValue(expression)) {
@@ -514,6 +514,29 @@ private <T> void injectFields(T objectToConfigure) {
         } while ((objectToConfigureClass = objectToConfigureClass.getSuperclass()) != null);
     }
 
+    /**
+     * If @Configuration() has value, this is used;
+     * if field is non-empty String, its value is used;
+     * otherwise, field name is used.
+     *
+     * @return Property key
+     */
+    private static <T> String getExpression(T objectToConfigure, Field field, Configuration configurationAnnotation) {
+        String expression = configurationAnnotation.value();
+        if ("".equals(configurationAnnotation.value())) {
+            expression = field.getName();
+            if (String.class.equals(field.getType())) {
+                try {
+                    String value = (String) field.get(objectToConfigure);
+                    if (value != null && value.length() > 0) {
+                        expression = value;
+                    }
+                } catch (IllegalAccessException  ile) { }
+            }
+        }
+        return expression;
+    }
+
     private boolean hasAnnotationDefaults(Configuration configurationAnnotation) {
         return !("N/A".equals(configurationAnnotation.defaultValue()) && configurationAnnotation.defaultValueFactory().equals(Configuration.EmptyValueFactory.class));
     }

constretto-core/src/test/java/org/constretto/ConstrettoConfigurationTest.java

@@ -25,7 +25,7 @@ public void constrettoShouldWorkWithNonExistingResources() {
         assertNotNull(configuration);
     }
 
-    @Test(expected = ConstrettoExpressionException.class) //TODO perhaps a more specific expeption
+    @Test(expected = ConstrettoExpressionException.class) //TODO perhaps a more specific exception
     public void shouldThrowExceptionIfTryingToMapWithoutNeededAllTagsProvided() throws Exception {
         new ConstrettoBuilder(false)
                 .createPropertiesStore()

constretto-core/src/test/java/org/constretto/internal/provider/ConfigurationAnnotationsTest.java

@@ -45,6 +45,7 @@ public void prepareTests() {
         setProperty("password", "password");
         setProperty("vendor", "derby");
         setProperty("version", "10");
+        setProperty("derby.system.home", "C:\\home\\Derby\\");
         setProperty("array", "[\"one\",\"two\",\"three\"]");
         setProperty("map", "{\"1\":\"10\",\"2\":\"20\"}");
         configuration = new ConstrettoBuilder().createSystemPropertiesStore().getConfiguration();
@@ -69,6 +70,7 @@ public void applyConfigrationToAnnotatedConfigurationObject() {
         assertEquals("username", customerDataSource.getUsername());
         assertEquals("jdbc://url", customerDataSource.getUrl());
         assertEquals("password", customerDataSource.getPassword());
+        assertEquals("C:\\home\\Derby\\", customerDataSource.homeDir);
         assertEquals(new Integer(10), customerDataSource.getVersion());
     }
 

constretto-core/src/test/java/org/constretto/internal/provider/helper/DataSourceConfiguration.java

@@ -33,6 +33,8 @@ public class DataSourceConfiguration {
     @Configuration("username")
     private String myUsername;
 
+    @Configuration
+    public String homeDir = "derby.system.home";
 
     @Configure
     public void configureMe(@Configuration String url, @Configuration("password") String secret) {