Refactor #384

Update the onAttributeChange method to return a ChangeSupport class that
can be used to handle release of resources (in the close method).

When a Config is released, it should call ChangeSupport.close to ensure
that the ConfigSource has a chance to properly release any resources
held by the callbacks.

* Add TCK test ConfigAccessorTest#testOnAttributeChange

Signed-off-by: Jeff Mesnil <[email protected]>

api/src/main/java/org/eclipse/microprofile/config/spi/ConfigSource.java

@@ -26,11 +26,13 @@
  *      Extracted the Config part out of DeltaSpike and proposed as Microprofile-Config cf41cf130bcaf5447ff8
  *   2016-11-14 - Emily Jiang / IBM Corp
  *      Methods renamed, JavaDoc and cleanup
- *  
+ *
  *
  *******************************************************************************/
 package org.eclipse.microprofile.config.spi;
 
+import java.io.Closeable;
+import java.io.Serializable;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Consumer;
@@ -164,18 +166,6 @@ default int getOrdinal() {
      */
     String getName();
 
-    /**
-     * Determines if this config source should be scanned for its list of properties.
-     *
-     * Generally, slow ConfigSources should return false here.
-     *
-     * @return {@code true} if this ConfigSource should be scanned for its list of properties,
-     *         {@code false} if it should not be scanned.
-     */
-    default boolean isScannable() {
-        return true;
-    }
-
     /**
      * The callback should get invoked if an attribute change got detected inside the ConfigSource.
      *
@@ -188,33 +178,42 @@ default boolean isScannable() {
     default ChangeSupport onAttributeChange(Consumer<Set<String>> callback) {
         // do nothing by default. Just for compat with older ConfigSources.
         // return unsupported to tell config that it must re-query this source every time
-        return ChangeSupport.UNSUPPORTED;
+        return () -> ChangeSupport.Type.UNSUPPORTED;
     }
 
     /**
      * What kind of change support this config source has.
      * <p>
      * {@link org.eclipse.microprofile.config.Config} implementations may use this information for internal optimizations.
      */
-    enum ChangeSupport {
-        /**
-         * Config change is supported, this config source will invoke the callback provided by
-         * {@link ConfigSource#onAttributeChange(Consumer)}.
-         * <p>
-         * Example: File based config source that watches the file for changes
-         */
-        SUPPORTED,
-        /**
-         * Config change is not supported. Configuration values can change, though this change is not reported back.
-         * <p>
-         * Example: LDAP based config source
-         */
-        UNSUPPORTED,
-        /**
-         * Configuration values cannot change for the lifetime of this {@link ConfigSource}.
-         * <p>
-         * Example: Environment variables config source, classpath resource config source
-         */
-        IMMUTABLE
+    interface ChangeSupport extends Closeable, Serializable {
+
+        enum Type {
+            /**
+             * Config change is supported, this config source will invoke the callback provided by
+             * {@link ConfigSource#onAttributeChange(Consumer)}.
+             * <p>
+             * Example: File based config source that watches the file for changes
+             */
+            SUPPORTED,
+            /**
+             * Config change is not supported. Configuration values can change, though this change is not reported back.
+             * <p>
+             * Example: LDAP based config source
+             */
+            UNSUPPORTED,
+            /**
+             * Configuration values cannot change for the lifetime of this {@link ConfigSource}.
+             * <p>
+             * Example: Environment variables config source, classpath resource config source
+             */
+            IMMUTABLE
+        }
+
+        Type getType();
+
+        @Override
+        default void close() {
+        }
     }
 }

tck/src/main/java/org/eclipse/microprofile/config/tck/ConfigAccessorTest.java

@@ -196,6 +196,21 @@ public void testCacheFor() throws Exception {
         Assert.assertEquals(val.getValue(), "secondvalue");
     }
 
+    @Test
+    public void testOnAttributeChange() {
+        String key = "tck.config.test.onattributechange.key";
+        ConfigurableConfigSource.configure(config, key, "firstvalue");
+
+        ConfigAccessor<String> val = config.access(key, String.class).cacheFor(Duration.ofMillis(30)).build();
+        Assert.assertEquals(val.getValue(), "firstvalue");
+
+        // immediately change the value on the ConfigurableConfigSource that will notify the Config of the change
+        ConfigurableConfigSource.configure(config, key, "secondvalue");
+
+        // we should see the new value right now as the ConfigurableConfigSource has notified that its attribute has changed
+        Assert.assertEquals(val.getValue(), "secondvalue");
+    }
+
     @Test
     public void testDefaultValue() {
         String key = "tck.config.test.javaconfig.somerandom.default.key";

tck/src/main/java/org/eclipse/microprofile/config/tck/configsources/ConfigurableConfigSource.java

@@ -64,14 +64,15 @@ public String getName() {
     @Override
     public ConfigSource.ChangeSupport onAttributeChange(Consumer<Set<String>> reportAttributeChange) {
         this.reportAttributeChange = reportAttributeChange;
-        return ChangeSupport.SUPPORTED;
+        return () -> ChangeSupport.Type.SUPPORTED;
     }
 
     public static void configure(Config cfg, String propertyName, String value) {
         for (ConfigSource configSource : cfg.getConfigSources()) {
             if (configSource instanceof ConfigurableConfigSource) {
-                ((ConfigurableConfigSource) configSource).properties.put(propertyName, value);
-                ((ConfigurableConfigSource) configSource).reportAttributeChange.accept(Collections.singleton(propertyName));
+                ConfigurableConfigSource configurableConfigSource = (ConfigurableConfigSource) configSource;
+                configurableConfigSource.properties.put(propertyName, value);
+                configurableConfigSource.reportAttributeChange.accept(Collections.singleton(propertyName));
                 return;
             }
         }