Add system property to pick HystrixDynamicProperties and made Archaiu…

…s Helper more private.

hystrix-core/src/main/java/com/netflix/hystrix/strategy/HystrixArchaiusHelper.java

@@ -0,0 +1,90 @@
+/**
+ * Copyright 2016 Netflix, Inc.
+ * <p/>
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p/>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p/>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.netflix.hystrix.strategy;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
+import com.netflix.hystrix.strategy.properties.HystrixDynamicProperties;
+
+/**
+ * @ExcludeFromJavadoc
+ * @author agentgt
+ */
+class HystrixArchaiusHelper {
+
+    /**
+     * To keep class loading minimal for those that have archaius in the classpath but choose not to use it.
+     * @ExcludeFromJavadoc
+     * @author agent
+     */
+    private static class LazyHolder {
+        private final static Method loadCascadedPropertiesFromResources;
+        private final static String CONFIG_MANAGER_CLASS = "com.netflix.config.ConfigurationManager";
+
+        static {
+            Method load = null;
+            try {
+                Class<?> configManager = Class.forName(CONFIG_MANAGER_CLASS);
+                load = configManager.getMethod("loadCascadedPropertiesFromResources", String.class);
+            } catch (Exception e) {
+            }
+
+            loadCascadedPropertiesFromResources = load;
+        }
+    }
+
+    /**
+     * @ExcludeFromJavadoc
+     */
+    static boolean isArchaiusV1Available() {
+        return LazyHolder.loadCascadedPropertiesFromResources != null;
+    }
+
+    static void loadCascadedPropertiesFromResources(String name) {
+        if (isArchaiusV1Available()) {
+            try {
+                LazyHolder.loadCascadedPropertiesFromResources.invoke(null, name);
+            } catch (IllegalAccessException e) {
+            } catch (IllegalArgumentException e) {
+            } catch (InvocationTargetException e) {
+            }
+        }
+    }
+
+    /**
+     * @ExcludeFromJavadoc
+     */
+    static HystrixDynamicProperties createArchaiusDynamicProperties() {
+        if (isArchaiusV1Available()) {
+            loadCascadedPropertiesFromResources("hystrix-plugins");
+            try {
+                Class<?> defaultProperties = Class.forName(
+                        "com.netflix.hystrix.strategy.properties.archaius" + ".HystrixDynamicPropertiesArchaius");
+                return (HystrixDynamicProperties) defaultProperties.newInstance();
+            } catch (ClassNotFoundException e) {
+                throw new RuntimeException(e);
+            } catch (InstantiationException e) {
+                throw new RuntimeException(e);
+            } catch (IllegalAccessException e) {
+                throw new RuntimeException(e);
+            }
+        }
+        // Fallback to System properties.
+        return null;
+    }
+
+}

hystrix-core/src/main/java/com/netflix/hystrix/strategy/HystrixPlugins.java

@@ -28,8 +28,8 @@
 import com.netflix.hystrix.strategy.metrics.HystrixMetricsPublisher;
 import com.netflix.hystrix.strategy.metrics.HystrixMetricsPublisherDefault;
 import com.netflix.hystrix.strategy.metrics.HystrixMetricsPublisherFactory;
-import com.netflix.hystrix.strategy.properties.HystrixArchaiusHelper;
 import com.netflix.hystrix.strategy.properties.HystrixDynamicProperties;
+import com.netflix.hystrix.strategy.properties.HystrixDynamicPropertiesSystemProperties;
 import com.netflix.hystrix.strategy.properties.HystrixPropertiesStrategy;
 import com.netflix.hystrix.strategy.properties.HystrixPropertiesStrategyDefault;
 
@@ -42,8 +42,8 @@
  * <li>default implementation</li>
  * </ol>
  * 
- * The exception to the above order is the {@link HystrixDynamicProperties} implmentation 
- * which is only loaded through the ServiceLoader (see the {@link HystrixPlugins#getDynamicProperties() getter} for more details).
+ * The exception to the above order is the {@link HystrixDynamicProperties} implementation 
+ * which is only loaded through <code>System.properties</code> or the ServiceLoader (see the {@link HystrixPlugins#getDynamicProperties() getter} for more details).
  * <p>
  * See the Hystrix GitHub Wiki for more information: <a href="https://github.com/Netflix/Hystrix/wiki/Plugins">https://github.com/Netflix/Hystrix/wiki/Plugins</a>.
  */
@@ -245,9 +245,10 @@ public HystrixPropertiesStrategy getPropertiesStrategy() {
      * <p>
      * The order of precedence for loading implementations is:
      * <ol>
+     * <li>System property of key: <code>hystrix.plugin.HystrixDynamicProperties.implementation</code> with the class as a value.</li>
      * <li>The {@link ServiceLoader}.</li>
-     * <li>An implementation based on Archaius if it is found in the classpath it is used.</li>
-     * <li>An implementation based on the {@link System#getProperties()}</li>
+     * <li>An implementation based on Archaius if it is found in the classpath is used.</li>
+     * <li>A fallback implementation based on the {@link System#getProperties()}</li>
      * </ol>
      * @return never <code>null</code>
      */
@@ -314,13 +315,13 @@ public void registerCommandExecutionHook(HystrixCommandExecutionHook impl) {
 
 
     private <T> T getPluginImplementation(Class<T> pluginClass) {
-        T p = getPluginImplementationViaProperties(pluginClass);
+        T p = getPluginImplementationViaProperties(pluginClass, dynamicProperties);
         if (p != null) return p;        
         return findService(pluginClass, classLoader);
     }
 
     @SuppressWarnings("unchecked")
-    private <T> T getPluginImplementationViaProperties(Class<T> pluginClass) {
+    private static <T> T getPluginImplementationViaProperties(Class<T> pluginClass, HystrixDynamicProperties dynamicProperties) {
         String classSimpleName = pluginClass.getSimpleName();
         // Check Archaius for plugin class.
         String propertyName = "hystrix.plugin." + classSimpleName + ".implementation";
@@ -348,9 +349,14 @@ private <T> T getPluginImplementationViaProperties(Class<T> pluginClass) {
 
 
     private static HystrixDynamicProperties resolveDynamicProperties(ClassLoader classLoader) {
-        HystrixDynamicProperties hp = findService(HystrixDynamicProperties.class, classLoader);
+        HystrixDynamicProperties hp = getPluginImplementationViaProperties(HystrixDynamicProperties.class, 
+                HystrixDynamicPropertiesSystemProperties.getInstance());
         if (hp != null) return hp;
-        return HystrixArchaiusHelper.createArchaiusDynamicProperties();
+        hp = findService(HystrixDynamicProperties.class, classLoader);
+        if (hp != null) return hp;
+        hp = HystrixArchaiusHelper.createArchaiusDynamicProperties();
+        if (hp != null) return hp;
+        return HystrixDynamicPropertiesSystemProperties.getInstance();
     }
 
     private static <T> T findService(