feat/OAK-12253 : add a mechanism to override FT defaults via system property

oak-core-spi/src/main/java/org/apache/jackrabbit/oak/spi/toggle/Feature.java

@@ -22,8 +22,11 @@
 import java.util.Collections;
 import java.util.concurrent.atomic.AtomicBoolean;
 
+import org.apache.jackrabbit.oak.commons.properties.SystemPropertySupplier;
 import org.apache.jackrabbit.oak.spi.whiteboard.Registration;
 import org.apache.jackrabbit.oak.spi.whiteboard.Whiteboard;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * A feature toggle to control new functionality. The default state of a feature
@@ -34,12 +37,20 @@
  * involves registering a feature toggle on the {@link Whiteboard} and
  * potentially comes with some overhead (e.g. when the whiteboard is based on
  * OSGi). Therefore, client code should not create a new feature, check the
- * state and then immediately release/close it again. Instead a feature should
+ * state and then immediately release/close it again. Instead, a feature should
  * be acquired initially, checked at runtime whenever needed and finally
  * released when the client component is destroyed.
+ * <p>
+ * The default state of {@code false} can be overridden by a system property
+ * using {@linkplain #newFeatureWithSystemPropertyDefault(String, Whiteboard)},
+ * in which case The property name is derived from the toggle name. This helps to quickly verify
+ * a new feature. For a toggle named {@code "foo"}, the system property name is
+ * {@code oak-feature.foo}.
  */
 public final class Feature implements Closeable {
 
+    private static final Logger LOG = LoggerFactory.getLogger(Feature.class);
+
     private final AtomicBoolean value;
 
     private final Registration registration;
@@ -49,6 +60,16 @@
         this.registration = registration;
     }
 
+    private static Feature internalNewFeatureWithSystemPropertyDefault(String name, Whiteboard whiteboard, boolean withSysPropDefault) {
+        // by default the initial value is false, but it can be overridden by a system property
+        AtomicBoolean value = withSysPropDefault ? new AtomicBoolean(
+                SystemPropertySupplier.create("oak-feature." + name, false).
+                        loggingTo(LOG).get()) : new AtomicBoolean();
+        FeatureToggle adapter = new FeatureToggle(name, value);
+        return new Feature(value, whiteboard.register(
+                FeatureToggle.class, adapter, Collections.emptyMap()));
+    }
+
     /**
      * Creates a new {@link Feature} with the given name and registers the
      * corresponding {@link FeatureToggle} on the {@link Whiteboard}.
@@ -60,10 +81,15 @@
      * @return the feature toggle.
      */
     public static Feature newFeature(String name, Whiteboard whiteboard) {
-        AtomicBoolean value = new AtomicBoolean();
-        FeatureToggle adapter = new FeatureToggle(name, value);
-        return new Feature(value, whiteboard.register(
-                FeatureToggle.class, adapter, Collections.emptyMap()));
+        return internalNewFeatureWithSystemPropertyDefault(name, whiteboard, false);
+    }
+
+    /**
+     * Same as {@linkplain #newFeature(String, Whiteboard)}, but with the initial state provided
+     * by a system property, named based on the feature's name.
+     */
+    public static Feature newFeatureWithSystemPropertyDefault(String name, Whiteboard whiteboard) {
+        return internalNewFeatureWithSystemPropertyDefault(name, whiteboard, true);
     }
 
     /**

oak-core-spi/src/main/java/org/apache/jackrabbit/oak/spi/toggle/package-info.java

@@ -16,7 +16,7 @@
  * specific language governing permissions and limitations
  * under the License.
  */
-@Version("1.0.0")
+@Version("1.1.0")
 package org.apache.jackrabbit.oak.spi.toggle;
 
 import org.osgi.annotation.versioning.Version;

oak-core-spi/src/test/java/org/apache/jackrabbit/oak/spi/toggle/FeatureToggleTest.java

@@ -28,6 +28,7 @@
 import org.junit.Test;
 
 import static org.apache.jackrabbit.oak.spi.toggle.Feature.newFeature;
+import static org.apache.jackrabbit.oak.spi.toggle.Feature.newFeatureWithSystemPropertyDefault;
 import static org.hamcrest.CoreMatchers.hasItems;
 import static org.hamcrest.Matchers.empty;
 import static org.hamcrest.core.Is.is;
@@ -50,6 +51,28 @@ public void disabledByDefault() {
         }
     }
 
+    @Test
+    public void defaultOverriddenAsTrue() {
+        String sysPropName = "oak-feature.my.toggle";
+        System.setProperty(sysPropName, "true");
+        try (Feature feature = newFeatureWithSystemPropertyDefault("my.toggle", whiteboard)) {
+            assertTrue(feature.isEnabled());
+        } finally {
+            System.clearProperty(sysPropName);
+        }
+    }
+
+    @Test
+    public void defaultOverriddenAsFalse() {
+        String sysPropName = "oak-feature.my.toggle";
+        System.setProperty(sysPropName, "false");
+        try (Feature feature = newFeatureWithSystemPropertyDefault("my.toggle", whiteboard)) {
+            assertFalse(feature.isEnabled());
+        } finally {
+            System.clearProperty(sysPropName);
+        }
+    }
+
     @Test
     public void register() {
         try (Feature feature = newFeature("my.toggle", whiteboard)) {

oak-core-spi/src/test/resources/logback-test.xml

@@ -34,4 +34,5 @@
     <appender-ref ref="file"/>
 </root>
 
+<logger name="org.apache.jackrabbit.oak.spi.toggle.Feature" level="INFO"/>
 </configuration>