INT-4313: GemfireMetadataSt: Add Listener support

JIRA: https://jira.springsource.org/browse/INT-4313

* Add `GemfireCacheListener` in `GemfireMetadataStore` to delegate cache
events to `MetadataStoreListener`s.
* Add GemfireMetadataStore cache listener tests.
* Update ascii doc.
* Addresses review comments.
* Some polishing to Java 8 style
* Some code style polishing
* Minor Doc improvement

spring-integration-gemfire/src/main/java/org/springframework/integration/gemfire/metadata/GemfireMetadataStore.java

@@ -16,11 +16,19 @@
 
 package org.springframework.integration.gemfire.metadata;
 
+import java.util.List;
+import java.util.Objects;
+import java.util.concurrent.CopyOnWriteArrayList;
+
 import org.apache.geode.cache.Cache;
+import org.apache.geode.cache.EntryEvent;
 import org.apache.geode.cache.Region;
 import org.apache.geode.cache.Scope;
+import org.apache.geode.cache.util.CacheListenerAdapter;
 
 import org.springframework.integration.metadata.ConcurrentMetadataStore;
+import org.springframework.integration.metadata.ListenableMetadataStore;
+import org.springframework.integration.metadata.MetadataStoreListener;
 import org.springframework.util.Assert;
 
 /**
@@ -30,22 +38,30 @@ import org.springframework.util.Assert;
  * restarts.
  *
  * @author Artem Bilan
+ * @author Venil Noronha
+ *
  * @since 4.0
  */
-public class GemfireMetadataStore implements ConcurrentMetadataStore {
+public class GemfireMetadataStore implements ListenableMetadataStore {
 
 	public static final String KEY = "MetaData";
 
+	private final GemfireCacheListener cacheListener = new GemfireCacheListener();
+
 	private final Region<String, String> region;
 
 	public GemfireMetadataStore(Cache cache) {
-		Assert.notNull(cache, "'cache' must not be null");
-		this.region = cache.<String, String>createRegionFactory().setScope(Scope.LOCAL).create(KEY);
+		this(Objects.requireNonNull(cache, "'cache' must not be null")
+				.<String, String>createRegionFactory()
+				.setScope(Scope.LOCAL)
+				.create(KEY));
 	}
 
 	public GemfireMetadataStore(Region<String, String> region) {
 		Assert.notNull(region, "'region' must not be null");
 		this.region = region;
+		this.region.getAttributesMutator()
+				.addCacheListener(this.cacheListener);
 	}
 
 	@Override
@@ -82,4 +98,40 @@ public class GemfireMetadataStore implements ConcurrentMetadataStore {
 		return this.region.remove(key);
 	}
 
+	@Override
+	public void addListener(MetadataStoreListener listener) {
+		Assert.notNull(listener, "'listener' must not be null");
+		this.cacheListener.listeners.add(listener);
+	}
+
+	@Override
+	public void removeListener(MetadataStoreListener listener) {
+		this.cacheListener.listeners.remove(listener);
+	}
+
+	private static class GemfireCacheListener extends CacheListenerAdapter<String, String> {
+
+		private final List<MetadataStoreListener> listeners = new CopyOnWriteArrayList<>();
+
+		GemfireCacheListener() {
+			super();
+		}
+
+		@Override
+		public void afterCreate(EntryEvent<String, String> event) {
+			this.listeners.forEach(listener -> listener.onAdd(event.getKey(), event.getNewValue()));
+		}
+
+		@Override
+		public void afterUpdate(EntryEvent<String, String> event) {
+			this.listeners.forEach(listener -> listener.onUpdate(event.getKey(), event.getNewValue()));
+		}
+
+		@Override
+		public void afterDestroy(EntryEvent<String, String> event) {
+			this.listeners.forEach(listener -> listener.onRemove(event.getKey(), event.getOldValue()));
+		}
+
+	}
+
 }

spring-integration-gemfire/src/test/java/org/springframework/integration/gemfire/metadata/GemfireMetadataStoreCacheListenerTests.java

@@ -0,0 +1,158 @@
+/*
+ * Copyright 2017 the original author or authors.
+ *
+ * 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
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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 org.springframework.integration.gemfire.metadata;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+
+import org.apache.geode.cache.Cache;
+import org.apache.geode.cache.CacheFactory;
+import org.apache.geode.cache.Region;
+import org.junit.After;
+import org.junit.AfterClass;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import org.springframework.integration.metadata.MetadataStoreListenerAdapter;
+import org.springframework.util.Assert;
+
+/**
+ * @author Venil Noronha
+ *
+ * @since 5.0
+ *
+ */
+public class GemfireMetadataStoreCacheListenerTests {
+
+	private static Cache cache;
+
+	private static GemfireMetadataStore metadataStore;
+
+	private static Region<Object, Object> region;
+
+	@BeforeClass
+	public static void startUp() throws Exception {
+		cache = new CacheFactory().create();
+		metadataStore = new GemfireMetadataStore(cache);
+		region = cache.getRegion(GemfireMetadataStore.KEY);
+	}
+
+	@AfterClass
+	public static void cleanUp() {
+		if (region != null) {
+			region.close();
+		}
+		if (cache != null) {
+			cache.close();
+			Assert.isTrue(cache.isClosed(), "Cache did not close after close() call");
+		}
+	}
+
+	@Before
+	@After
+	public void setup() {
+		if (region != null) {
+			region.clear();
+		}
+	}
+
+	@Test
+	public void testAdd() throws InterruptedException {
+		String testKey = "key";
+		String testValue = "value";
+
+		CountDownLatch latch = new CountDownLatch(1);
+		AtomicReference<String> actualKey = new AtomicReference<>();
+		AtomicReference<String> actualValue = new AtomicReference<>();
+		metadataStore.addListener(new MetadataStoreListenerAdapter() {
+
+			@Override
+			public void onAdd(String key, String value) {
+				actualKey.set(key);
+				actualValue.set(value);
+				latch.countDown();
+			}
+
+		});
+
+		metadataStore.put(testKey, testValue);
+		latch.await(10, TimeUnit.SECONDS);
+
+		assertEquals(testKey, actualKey.get());
+		assertEquals(testValue, actualValue.get());
+	}
+
+	@Test
+	public void testRemove() throws InterruptedException {
+		String testKey = "key";
+		String testValue = "value";
+
+		CountDownLatch latch = new CountDownLatch(1);
+		AtomicReference<String> actualKey = new AtomicReference<>();
+		AtomicReference<String> actualValue = new AtomicReference<>();
+		metadataStore.addListener(new MetadataStoreListenerAdapter() {
+
+			@Override
+			public void onRemove(String key, String oldValue) {
+				actualKey.set(key);
+				actualValue.set(oldValue);
+				latch.countDown();
+			}
+
+		});
+
+		metadataStore.put(testKey, testValue);
+		metadataStore.remove(testKey);
+		latch.await(10, TimeUnit.SECONDS);
+
+		assertEquals(testKey, actualKey.get());
+		assertEquals(testValue, actualValue.get());
+	}
+
+	@Test
+	public void testUpdate() throws InterruptedException {
+		String testKey = "key";
+		String testValue = "value";
+		String testNewValue = "new-value";
+
+		CountDownLatch latch = new CountDownLatch(1);
+		AtomicReference<String> actualKey = new AtomicReference<>();
+		AtomicReference<String> actualValue = new AtomicReference<>();
+		metadataStore.addListener(new MetadataStoreListenerAdapter() {
+
+			@Override
+			public void onUpdate(String key, String newValue) {
+				actualKey.set(key);
+				actualValue.set(newValue);
+				latch.countDown();
+			}
+
+		});
+
+		metadataStore.put(testKey, testValue);
+		metadataStore.put(testKey, testNewValue);
+		latch.await(10, TimeUnit.SECONDS);
+
+		assertEquals(testKey, actualKey.get());
+		assertEquals(testNewValue, actualValue.get());
+	}
+
+}

src/reference/asciidoc/gemfire.adoc

@@ -192,7 +192,7 @@ Another constructor requires `Cache` and the `Region` will be created with `GLOB
 [[gemfire-metadata-store]]
 === Gemfire Metadata Store
 
-As of _Spring Integration 4.0_, a new Gemfire-based `MetadataStore` (<<metadata-store>>) implementation is available.
+As of _version 4.0_, a new Gemfire-based `MetadataStore` (<<metadata-store>>) implementation is available.
 The `GemfireMetadataStore` can be used to maintain metadata state across application restarts.
 This new `MetadataStore` implementation can be used with adapters such as:
 
@@ -202,11 +202,24 @@ This new `MetadataStore` implementation can be used with adapters such as:
 * <<ftp-inbound>>
 * <<sftp-inbound>>
 
-
-
 In order to instruct these adapters to use the new `GemfireMetadataStore`, simply declare a Spring bean using the bean name *metadataStore*.
 The _Twitter Inbound Channel Adapter_ and the _Feed Inbound Channel Adapter_ will both automatically pick up and use the declared `GemfireMetadataStore`.
 
 NOTE: The `GemfireMetadataStore` also implements `ConcurrentMetadataStore`, allowing it to be reliably shared across multiple application instances where only one instance will be allowed to store or modify a key's value.
 These methods give various levels of concurrency guarantees based on the scope and data policy of the region.
 They are implemented in the peer cache and client/server cache but are disallowed in peer Regions having NORMAL or EMPTY data policies.
+
+NOTE: Since _version 5.0_, the `GemfireMetadataStore` also implements `ListenableMetadataStore`, allowing users to listen to cache events by providing `MetadataStoreListener` instances to the store:
+
+[source,java]
+----
+GemfireMetadataStore metadataStore = new GemfireMetadataStore(cache);
+metadataStore.addListener(new MetadataStoreListenerAdapter() {
+
+    @Override
+    public void onAdd(String key, String value) {
+         ...
+    }
+
+});
+----

src/reference/asciidoc/whats-new.adoc

@@ -95,6 +95,10 @@ The `ObjectToMapTransformer` can now be supplied with a customised `JsonObjectMa
 
 See <<aggregator-spel>> for more information.
 
+The `@GlobalChannelInterceptor` annotation and `<int:channel-interceptor>` now support negative patterns (via `!` prepending) for component names matching.
+
+See <<global-channel-configuration-interceptors>> for more information.
+
 ==== Gateway Changes
 
 The gateway now correctly sets the `errorChannel` header when the gateway method has a `void` return type and an error channel is provided.
@@ -273,8 +277,8 @@ A `ByteArrayElasticRawDeserializer` has been added without `maxMessageSize` cont
 
 See <<ip>> for more information.
 
-==== GlobalChannelInterceptor changes
+==== Gemfire Changes
 
-The `@GlobalChannelInterceptor` annotation and `<int:channel-interceptor>` now support negative patterns (via `!` prepending) for component names matching.
+The `GemfireMetadataStore` now implements `ListenableMetadataStore`, allowing users to listen to cache events by providing `MetadataStoreListener` instances to the store.
 
-See <<global-channel-configuration-interceptors>> for more information.
+See <<gemfire>> for more information.