Custom string substitutors functionality

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

@@ -9,6 +9,15 @@
 package org.aeonbits.owner;
 
 
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.TYPE;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+import static java.util.concurrent.TimeUnit.SECONDS;
+import static org.aeonbits.owner.Config.HotReloadType.SYNC;
+import static org.aeonbits.owner.Config.LoadType.FIRST;
+import static org.aeonbits.owner.Util.ignore;
+import static org.aeonbits.owner.Util.reverse;
+
 import java.io.IOException;
 import java.io.Serializable;
 import java.lang.annotation.Documented;
@@ -19,15 +28,6 @@
 import java.util.Properties;
 import java.util.concurrent.TimeUnit;
 
-import static java.lang.annotation.ElementType.METHOD;
-import static java.lang.annotation.ElementType.TYPE;
-import static java.lang.annotation.RetentionPolicy.RUNTIME;
-import static java.util.concurrent.TimeUnit.SECONDS;
-import static org.aeonbits.owner.Config.HotReloadType.SYNC;
-import static org.aeonbits.owner.Config.LoadType.FIRST;
-import static org.aeonbits.owner.Util.ignore;
-import static org.aeonbits.owner.Util.reverse;
-
 /**
  * Marker interface that must be implemented by all Config sub-interfaces.
  * <p>
@@ -329,4 +329,16 @@ enum DisableableFeature {
         Class<? extends Converter> value();
     }
 
+    /**
+     * Registers {@link Substitutor} classes, with given names, to allow the user to define custom
+     * substitutor logic when expanding variables in property strings.
+     */
+    @Retention(RUNTIME)
+    @Target(TYPE)
+    @Documented
+    @interface SubstitutorClasses {
+        String[] names();
+        Class<? extends Substitutor>[] classes();
+    }
+
 }

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

@@ -8,13 +8,13 @@
 
 package org.aeonbits.owner;
 
-import org.aeonbits.owner.loaders.Loader;
+import static java.lang.reflect.Proxy.newProxyInstance;
 
 import java.util.Map;
 import java.util.Properties;
 import java.util.concurrent.ScheduledExecutorService;
 
-import static java.lang.reflect.Proxy.newProxyInstance;
+import org.aeonbits.owner.loaders.Loader;
 
 /**
  * Default implementation for {@link Factory}.
@@ -39,7 +39,7 @@ public <T extends Config> T create(Class<? extends T> clazz, Map<?, ?>... import
         VariablesExpander expander = new VariablesExpander(props);
         PropertiesManager manager = new PropertiesManager(clazz, new Properties(), scheduler, expander, loadersManager,
                 imports);
-        PropertiesInvocationHandler handler = new PropertiesInvocationHandler(manager);
+        PropertiesInvocationHandler handler = new PropertiesInvocationHandler(manager, clazz);
         T proxy = (T) newProxyInstance(clazz.getClassLoader(), interfaces, handler);
         handler.setProxy(proxy);
         return proxy;

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

@@ -0,0 +1,24 @@
+package org.aeonbits.owner;
+
+import java.io.Serializable;
+import java.util.Properties;
+
+
+final class DefaultSubstitutor implements Substitutor, Serializable {
+
+    private final Properties variables;
+
+    DefaultSubstitutor(Properties props) {
+        variables = props;
+    }
+
+    public String replace(String strToReplace) {
+        return variables.getProperty(strToReplace);
+    }
+
+    @Override
+    public String toString() {
+        return variables.toString();
+    }
+
+}

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

@@ -8,6 +8,14 @@
 
 package org.aeonbits.owner;
 
+import static org.aeonbits.owner.Config.DisableableFeature.PARAMETER_FORMATTING;
+import static org.aeonbits.owner.Config.DisableableFeature.VARIABLE_EXPANSION;
+import static org.aeonbits.owner.Converters.convert;
+import static org.aeonbits.owner.PropertiesMapper.key;
+import static org.aeonbits.owner.Util.isFeatureDisabled;
+import static org.aeonbits.owner.util.Reflection.invokeDefaultMethod;
+import static org.aeonbits.owner.util.Reflection.isDefault;
+
 import java.io.Serializable;
 import java.lang.reflect.InvocationHandler;
 import java.lang.reflect.InvocationTargetException;
@@ -16,14 +24,7 @@
 import java.util.LinkedList;
 import java.util.List;
 
-import static org.aeonbits.owner.Config.DisableableFeature.PARAMETER_FORMATTING;
-import static org.aeonbits.owner.Config.DisableableFeature.VARIABLE_EXPANSION;
-import static org.aeonbits.owner.Converters.convert;
-import static org.aeonbits.owner.PropertiesManager.Delegate;
-import static org.aeonbits.owner.PropertiesMapper.key;
-import static org.aeonbits.owner.Util.isFeatureDisabled;
-import static org.aeonbits.owner.util.Reflection.invokeDefaultMethod;
-import static org.aeonbits.owner.util.Reflection.isDefault;
+import org.aeonbits.owner.PropertiesManager.Delegate;
 
 /**
  * This {@link InvocationHandler} receives method calls from the delegate instantiated by {@link ConfigFactory} and maps
@@ -44,9 +45,9 @@ class PropertiesInvocationHandler implements InvocationHandler, Serializable {
     private final StrSubstitutor substitutor;
     final PropertiesManager propertiesManager;
 
-    PropertiesInvocationHandler(PropertiesManager manager) {
+    PropertiesInvocationHandler(PropertiesManager manager, Class<? extends Config> clazz) {
         this.propertiesManager = manager;
-        this.substitutor = new StrSubstitutor(manager.load());
+        this.substitutor = new StrSubstitutor(manager.load(), clazz);
     }
 
     public Object invoke(Object proxy, Method invokedMethod, Object... args) throws Throwable {

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

@@ -8,13 +8,18 @@
 
 package org.aeonbits.owner;
 
+import static java.util.regex.Pattern.compile;
+import static org.aeonbits.owner.Util.fixBackslashForRegex;
+import static org.aeonbits.owner.Util.unsupported;
+
 import java.io.Serializable;
+import java.util.HashMap;
+import java.util.Map;
 import java.util.Properties;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
-import static java.util.regex.Pattern.compile;
-import static org.aeonbits.owner.Util.fixBackslashForRegex;
+import org.aeonbits.owner.Config.SubstitutorClasses;
 
 /**
  * <p>
@@ -48,8 +53,10 @@
  */
 class StrSubstitutor implements Serializable {
 
-    private final Properties values;
     private static final Pattern PATTERN = compile("\\$\\{(.+?)\\}");
+    private static final String DEFAULT_SUBSTITUTOR_NAME = "";
+    private static final int TO_SIZE_2 = 2;
+    private final Map<String, Substitutor> substitutors = new HashMap<String, Substitutor>();
 
     /**
      * Creates a new instance and initializes it. Uses defaults for variable prefix and suffix and the escaping
@@ -58,7 +65,41 @@ class StrSubstitutor implements Serializable {
      * @param values the variables' values, may be null
      */
     StrSubstitutor(Properties values) {
-        this.values = values;
+        substitutors.put(DEFAULT_SUBSTITUTOR_NAME, new DefaultSubstitutor(values));
+    }
+
+    StrSubstitutor(Properties values, Class<? extends Config> clazz) {
+        substitutors.put(DEFAULT_SUBSTITUTOR_NAME, new DefaultSubstitutor(values));
+        addCustomSubstitutors(clazz);
+    }
+
+    private void addCustomSubstitutors(Class<? extends Config> configClazz) {
+        SubstitutorClasses annotation = configClazz.getAnnotation(SubstitutorClasses.class);
+        if (annotation != null) {
+            checkSameSize(annotation);
+            for (int i = 0; i < annotation.names().length; i++) {
+                String name = annotation.names()[i];
+                Class<? extends Substitutor> clazz = annotation.classes()[i];
+                try {
+                    substitutors.put(name, clazz.newInstance());
+                } catch (Exception e) {
+                    throw unsupported(e,
+                            "Substitutor class '%s' cannot be instantiated; see the cause below in the stack trace",
+                            clazz.getCanonicalName());
+                }
+            }
+        }
+
+    }
+
+    private void checkSameSize(SubstitutorClasses annotation) {
+        int numOfNames = annotation.names().length;
+        int numOfClasses = annotation.classes().length;
+        if (numOfNames != numOfClasses) {
+            throw unsupported(
+                    "Mismatch in number of names (%s) and classes (%s) in annotation %s",
+                    numOfNames, numOfClasses, annotation);
+        }
     }
 
     /**
@@ -74,13 +115,29 @@ String replace(String source) {
         Matcher m = PATTERN.matcher(source);
         StringBuffer sb = new StringBuffer();
         while (m.find()) {
-            String var = m.group(1);
-            String value = values.getProperty(var);
+            String value = replaceValueUsingSubstitutors(m.group(1));
             String replacement = (value != null) ? replace(value) : "";
             m.appendReplacement(sb, fixBackslashForRegex(replacement));
         }
         m.appendTail(sb);
         return sb.toString();
     }
 
+    private String replaceValueUsingSubstitutors(final String strToReplace) {
+        String name = DEFAULT_SUBSTITUTOR_NAME;
+        String value = strToReplace;
+        if (strToReplace.contains(":")) {
+            String[] pair = strToReplace.split(":", TO_SIZE_2);
+            name = pair[0];
+            value = pair[1];
+        }
+        if (name.equals(DEFAULT_SUBSTITUTOR_NAME)) {
+            return substitutors.get(DEFAULT_SUBSTITUTOR_NAME).replace(strToReplace);
+        }
+        if (substitutors.containsKey(name)) {
+            return substitutors.get(name).replace(value);
+        }
+        return substitutors.get(DEFAULT_SUBSTITUTOR_NAME).replace(strToReplace);
+    }
+
 }

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

@@ -0,0 +1,21 @@
+package org.aeonbits.owner;
+
+import org.aeonbits.owner.Config.SubstitutorClasses;
+
+/**
+ * Substitutor interface specifies how to provide a custom substitutor mechanism when replacing
+ * variables in strings. Substitutors are registered by name and implementation class using
+ * {@link SubstitutorClasses} annotation. For example this string "${name:some-value}" the
+ * "some-value" part will be sent to the Substitutor implementation registered
+ * with the name "name".
+ */
+public interface Substitutor {
+
+    /**
+     * Replaces the given {@code strToReplace} to something custom.
+     * 
+     * @param strToReplace the value to replace
+     * @return the replacement value
+     */
+    String replace(String strToReplace);
+}

owner/src/test/java/org/aeonbits/owner/PropertiesInvocationHandlerTest.java

@@ -8,20 +8,20 @@
 
 package org.aeonbits.owner;
 
-import org.junit.Before;
-import org.junit.Test;
-import org.junit.runner.RunWith;
-import org.mockito.Mock;
-import org.mockito.Spy;
-import org.mockito.runners.MockitoJUnitRunner;
+import static org.mockito.Matchers.eq;
+import static org.mockito.Mockito.verify;
 
 import java.io.PrintStream;
 import java.io.PrintWriter;
 import java.util.Properties;
 import java.util.concurrent.ScheduledExecutorService;
 
-import static org.mockito.Matchers.eq;
-import static org.mockito.Mockito.verify;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.Spy;
+import org.mockito.runners.MockitoJUnitRunner;
 
 /**
  * @author Luigi R. Viggiano
@@ -47,7 +47,7 @@ interface Dummy extends Config {}
     @Before
     public void before() {
         PropertiesManager loader = new PropertiesManager(Dummy.class, properties, scheduler, expander, loaders);
-        handler = new PropertiesInvocationHandler(loader);
+        handler = new PropertiesInvocationHandler(loader, Dummy.class);
     }
 
     @Test