INT-3387: MessageGroupStore Improvements

JIRA: https://jira.spring.io/browse/INT-3387,
https://jira.spring.io/browse/INT-3806

* Introduce
```
MessageGroupStore

void addMessagesToGroup(Object groupId, Message<?>... messages);
```
And implement it in all stores.

* Use new `addMessagesToGroup` where it is reasonable, e.g. `DelayHandler`
* Optimize test-case to use a new store method (where it is possible)
* Fix timing delays in the `JdbcMessageStoreTests`
* Introduce `PersistentMessageGroup`
* Add `AbstractMessageGroupStore#proxyMessageGroupForLazyLoad` to wrap the raw `MessageGroup` to the `PersistentMessageGroup` for lazy-load
* Rework `MessageGroupMetadata` do not be `immutable` and allow to store/restore in the `AbstractKeyValueMessageStore` only the `MessageGroupMetadata`
* Refactor `ResequencingMessageHandler` and `SequenceSizeReleaseStrategy` a bit for better performance when interact with the `MessageGroup`
* Add `AbstractMessageGroupStore#setLazyLoadMessageGroups` to switch off the `lazy-load` behavior and restore the previous full `MessageGroup` logic
* Add `What's New` note and `message-store.adoc` paragraph for the lazy-load functionality

`GroupType.PERSISTENT` and not lazy by default

PR Comments

Fix `JdbcMessageStoreTests` timing issues

Address PR comments

* Add performance test to the `ConfigurableMongoDbMessageGroupStoreTests`
* Add JavaDocs for the `MessageGroupFactory` methods
* Add `log4j.properties` into the `test` MongoDB module for better traceability
* Fix `JdbcMessageStore#getOneMessageFromGroup()` over the `doPollForMessage()` delegation.
The `jdbcTemplate.queryForObject()` requires exactly one and only one raw in `resultSet`
* Add performance test results into the `message-store.adoc`

spring-integration-core/src/main/java/org/springframework/integration/aggregator/CorrelatingMessageBarrier.java

@@ -95,7 +95,7 @@ public class CorrelatingMessageBarrier extends AbstractMessageHandler implements
 		Object correlationKey = this.correlationStrategy.getCorrelationKey(message);
 		Object lock = getLock(correlationKey);
 		synchronized (lock) {
-			this.store.addMessageToGroup(correlationKey, message);
+			this.store.addMessagesToGroup(correlationKey, message);
 		}
 		if (log.isDebugEnabled()) {
 			log.debug(String.format("Handled message for key [%s]: %s.", correlationKey, message));

spring-integration-core/src/main/java/org/springframework/integration/aggregator/ResequencingMessageHandler.java

@@ -18,7 +18,6 @@ package org.springframework.integration.aggregator;
 
 import java.util.Collection;
 
-import org.springframework.integration.IntegrationMessageHeaderAccessor;
 import org.springframework.integration.store.MessageGroup;
 import org.springframework.integration.store.MessageGroupStore;
 import org.springframework.integration.store.SimpleMessageStore;
@@ -74,12 +73,9 @@ public class ResequencingMessageHandler extends AbstractCorrelatingMessageHandle
 
 	@Override
 	protected void afterRelease(MessageGroup messageGroup, Collection<Message<?>> completedMessages, boolean timeout) {
-		int size = messageGroup.getMessages().size();
-		int sequenceSize = 0;
-		Message<?> message = messageGroup.getOne();
-		if (message != null) {
-			sequenceSize = new IntegrationMessageHeaderAccessor(message).getSequenceSize();
-		}
+		int size = messageGroup.size();
+		int sequenceSize = messageGroup.getSequenceSize();
+
 		// If there is no sequence then it must be incomplete or unbounded
 		if (sequenceSize > 0 && sequenceSize == size) {
 			remove(messageGroup);

spring-integration-core/src/main/java/org/springframework/integration/aggregator/SequenceSizeReleaseStrategy.java

@@ -36,6 +36,7 @@ import org.springframework.messaging.Message;
  * @author Dave Syer
  * @author Iwein Fuld
  * @author Oleg Zhurakousky
+ * @author Artem Bilan
  * @author Enrique Rodríguez
  */
 public class SequenceSizeReleaseStrategy implements ReleaseStrategy {
@@ -55,9 +56,9 @@ public class SequenceSizeReleaseStrategy implements ReleaseStrategy {
 	}
 
 	/**
-	 * Flag that determines if partial sequences are allowed. If true then as soon as enough messages arrive that can be
-	 * ordered they will be released, provided they all have sequence numbers greater than those already released.
-	 *
+	 * Flag that determines if partial sequences are allowed. If true then as soon as
+	 * enough messages arrive that can be ordered they will be released, provided they
+	 * all have sequence numbers greater than those already released.
 	 * @param releasePartialSequences true when partial sequences should be released.
 	 */
 	public void setReleasePartialSequences(boolean releasePartialSequences) {
@@ -69,13 +70,12 @@ public class SequenceSizeReleaseStrategy implements ReleaseStrategy {
 
 		boolean canRelease = false;
 
-		Collection<Message<?>> messages = messageGroup.getMessages();
-
-		if (this.releasePartialSequences && !messages.isEmpty()) {
-
+		int size = messageGroup.size();
+		if (this.releasePartialSequences && size > 0) {
 			if (logger.isTraceEnabled()) {
 				logger.trace("Considering partial release of group [" + messageGroup + "]");
 			}
+			Collection<Message<?>> messages = messageGroup.getMessages();
 			Message<?> minMessage = Collections.min(messages, this.comparator);
 
 			int nextSequenceNumber = new IntegrationMessageHeaderAccessor(minMessage).getSequenceNumber();
@@ -86,13 +86,11 @@ public class SequenceSizeReleaseStrategy implements ReleaseStrategy {
 			}
 		}
 		else {
-			int size = messages.size();
-
 			if (size == 0) {
 				canRelease = true;
 			}
 			else {
-				int sequenceSize = new IntegrationMessageHeaderAccessor(messageGroup.getOne()).getSequenceSize();
+				int sequenceSize = messageGroup.getSequenceSize();
 				// If there is no sequence then it must be incomplete....
 				if (sequenceSize == size) {
 					canRelease = true;

spring-integration-core/src/main/java/org/springframework/integration/store/AbstractKeyValueMessageStore.java

@@ -94,38 +94,62 @@ public abstract class AbstractKeyValueMessageStore extends AbstractMessageGroupS
 	 */
 	@Override
 	public MessageGroup getMessageGroup(Object groupId) {
-		return buildMessageGroup(groupId, false);
+		MessageGroupMetadata metadata = getGroupMetadata(groupId);
+		if (metadata != null) {
+
+			MessageGroup messageGroup = getMessageGroupFactory()
+					.create(this, groupId, metadata.getTimestamp(), metadata.isComplete());
+			messageGroup.setLastModified(metadata.getLastModified());
+			messageGroup.setLastReleasedMessageSequenceNumber(metadata.getLastReleasedMessageSequenceNumber());
+			return messageGroup;
+		}
+		else {
+			return new SimpleMessageGroup(groupId);
+		}
 	}
 
-
-	/**
-	 * Add a Message to the group with the provided group ID.
-	 */
 	@Override
-	public MessageGroup addMessageToGroup(Object groupId, Message<?> message) {
+	public MessageGroupMetadata getGroupMetadata(Object groupId) {
 		Assert.notNull(groupId, "'groupId' must not be null");
-		Assert.notNull(message, "'message' must not be null");
+		Object mgm = this.doRetrieve(MESSAGE_GROUP_KEY_PREFIX + groupId);
+		if (mgm != null) {
+			Assert.isInstanceOf(MessageGroupMetadata.class, mgm);
+			return (MessageGroupMetadata) mgm;
+		}
+		return null;
+	}
 
-		// add message as is to the MG accessible by the caller
-		MessageGroup messageGroup = getMessageGroup(groupId);
+	@Override
+	public void addMessagesToGroup(Object groupId, Message<?>... messages) {
+		Assert.notNull(groupId, "'groupId' must not be null");
+		Assert.notNull(messages, "'messages' must not be null");
 
-		messageGroup.add(message);
+		MessageGroupMetadata metadata = getGroupMetadata(groupId);
+		SimpleMessageGroup group = null;
+		if (metadata == null) {
+			group = new SimpleMessageGroup(groupId);
+		}
 
-		// enrich Message with additional headers and add it to MS
-		Message<?> enrichedMessage = enrichMessage(message);
+		for (Message<?> message : messages) {
+			// enrich Message with additional headers and add it to MS
+			Message<?> enrichedMessage = enrichMessage(message);
+			addMessage(enrichedMessage);
+			if (metadata != null) {
+				metadata.add(enrichedMessage.getHeaders().getId());
+			}
+			else {
+				group.add(enrichedMessage);
+			}
+		}
 
-		addMessage(enrichedMessage);
+		if (group != null) {
+			metadata = new MessageGroupMetadata(group);
+		}
 
-		// build raw MessageGroup and add enriched Message to it
-		MessageGroup rawGroup = buildMessageGroup(groupId, true);
-		rawGroup.setLastModified(System.currentTimeMillis());
-		rawGroup.add(enrichedMessage);
+		metadata.setLastModified(System.currentTimeMillis());
 
 		// store MessageGroupMetadata built from enriched MG
-		doStore(MESSAGE_GROUP_KEY_PREFIX + groupId, new MessageGroupMetadata(rawGroup));
-
-		// return clean MG
-		return getMessageGroup(groupId);
+		doStore(MESSAGE_GROUP_KEY_PREFIX + groupId, metadata);
 	}
 
 	/**
@@ -137,32 +161,17 @@ public abstract class AbstractKeyValueMessageStore extends AbstractMessageGroupS
 		Assert.notNull(groupId, "'groupId' must not be null");
 		Assert.notNull(messageToRemove, "'messageToRemove' must not be null");
 
-		// build raw MG
-		MessageGroup rawGroup = buildMessageGroup(groupId, true);
+		UUID id = messageToRemove.getHeaders().getId();
+		removeMessage(id);
 
-		// create a clean instance of
-		MessageGroup messageGroup = normalizeSimpleMessageGroup(rawGroup);
-
-
-		Message<?> actualMessageToRemove = null;
-
-		for (Message<?> message : rawGroup.getMessages()) {
-			if (message.getHeaders().getId().equals(messageToRemove.getHeaders().getId())) {
-				actualMessageToRemove = message;
-				break;
-			}
+		MessageGroupMetadata metadata = getGroupMetadata(groupId);
+		if (metadata != null) {
+			metadata.remove(id);
+			metadata.setLastModified(System.currentTimeMillis());
+			doStore(MESSAGE_GROUP_KEY_PREFIX + groupId, metadata);
 		}
 
-		if (actualMessageToRemove != null) {
-			rawGroup.remove(actualMessageToRemove);
-			removeMessage(messageToRemove.getHeaders().getId());
-			rawGroup.setLastModified(System.currentTimeMillis());
-
-			doStore(MESSAGE_GROUP_KEY_PREFIX + groupId, new MessageGroupMetadata(rawGroup));
-			messageGroup = getMessageGroup(groupId);
-		}
-
-		return messageGroup;
+		return getMessageGroup(groupId);
 	}
 
 
@@ -188,10 +197,12 @@ public abstract class AbstractKeyValueMessageStore extends AbstractMessageGroupS
 	@Override
 	public void completeGroup(Object groupId) {
 		Assert.notNull(groupId, "'groupId' must not be null");
-		MessageGroup messageGroup = buildMessageGroup(groupId, true);
-		messageGroup.complete();
-		messageGroup.setLastModified(System.currentTimeMillis());
-		doStore(MESSAGE_GROUP_KEY_PREFIX + groupId, new MessageGroupMetadata(messageGroup));
+		MessageGroupMetadata metadata = getGroupMetadata(groupId);
+		if (metadata != null) {
+			metadata.complete();
+			metadata.setLastModified(System.currentTimeMillis());
+			doStore(MESSAGE_GROUP_KEY_PREFIX + groupId, metadata);
+		}
 	}
 
 	/**
@@ -215,37 +226,62 @@ public abstract class AbstractKeyValueMessageStore extends AbstractMessageGroupS
 	@Override
 	public void setLastReleasedSequenceNumberForGroup(Object groupId, int sequenceNumber) {
 		Assert.notNull(groupId, "'groupId' must not be null");
-		MessageGroup messageGroup = buildMessageGroup(groupId, true);
-		messageGroup.setLastReleasedMessageSequenceNumber(sequenceNumber);
-		messageGroup.setLastModified(System.currentTimeMillis());
-		doStore(MESSAGE_GROUP_KEY_PREFIX + groupId, new MessageGroupMetadata(messageGroup));
+		MessageGroupMetadata metadata = getGroupMetadata(groupId);
+		if (metadata == null) {
+			SimpleMessageGroup messageGroup = new SimpleMessageGroup(groupId);
+			metadata = new MessageGroupMetadata(messageGroup);
+		}
+		metadata.setLastReleasedMessageSequenceNumber(sequenceNumber);
+		metadata.setLastModified(System.currentTimeMillis());
+		doStore(MESSAGE_GROUP_KEY_PREFIX + groupId, metadata);
 	}
 
 	@Override
 	public Message<?> pollMessageFromGroup(Object groupId) {
-		Assert.notNull(groupId, "'groupId' must not be null");
-		Object mgm = doRetrieve(MESSAGE_GROUP_KEY_PREFIX + groupId);
-		if (mgm != null) {
-			Assert.isInstanceOf(MessageGroupMetadata.class, mgm);
-			MessageGroupMetadata messageGroupMetadata = (MessageGroupMetadata) mgm;
-
-			UUID firstId = messageGroupMetadata.firstId();
+		MessageGroupMetadata groupMetadata = getGroupMetadata(groupId);
+		if (groupMetadata != null) {
+			UUID firstId = groupMetadata.firstId();
 			if (firstId != null) {
-				messageGroupMetadata.remove(firstId);
-				messageGroupMetadata.setLastModified(System.currentTimeMillis());
-				doStore(MESSAGE_GROUP_KEY_PREFIX + groupId, messageGroupMetadata);
+				groupMetadata.remove(firstId);
+				groupMetadata.setLastModified(System.currentTimeMillis());
+				doStore(MESSAGE_GROUP_KEY_PREFIX + groupId, groupMetadata);
 				return removeMessage(firstId);
 			}
 		}
 		return null;
 	}
 
+	@Override
+	public Message<?> getOneMessageFromGroup(Object groupId) {
+		MessageGroupMetadata groupMetadata = getGroupMetadata(groupId);
+		if (groupMetadata != null) {
+			UUID messageId = groupMetadata.firstId();
+			if (messageId != null) {
+				return getMessage(messageId);
+			}
+		}
+		return null;
+	}
+
+	@Override
+	public Collection<Message<?>> getMessagesForGroup(Object groupId) {
+		MessageGroupMetadata groupMetadata = getGroupMetadata(groupId);
+		ArrayList<Message<?>> messages = new ArrayList<Message<?>>();
+		if (groupMetadata != null) {
+			Iterator<UUID> messageIds = groupMetadata.messageIdIterator();
+			while (messageIds.hasNext()) {
+				messages.add(getMessage(messageIds.next()));
+			}
+		}
+		return messages;
+	}
+
 	@Override
 	@SuppressWarnings("unchecked")
 	public Iterator<MessageGroup> iterator() {
 		final Iterator<?> idIterator = normalizeKeys(
 				(Collection<String>) doListKeys(MESSAGE_GROUP_KEY_PREFIX + "*"))
-					.iterator();
+				.iterator();
 		return new MessageGroupIterator(idIterator);
 	}
 
@@ -266,13 +302,13 @@ public abstract class AbstractKeyValueMessageStore extends AbstractMessageGroupS
 
 	@Override
 	public int messageGroupSize(Object groupId) {
-		Object mgm = doRetrieve(MESSAGE_GROUP_KEY_PREFIX + groupId);
+		MessageGroupMetadata mgm = getGroupMetadata(groupId);
 		if (mgm != null) {
-			Assert.isInstanceOf(MessageGroupMetadata.class, mgm);
-			MessageGroupMetadata messageGroupMetadata = (MessageGroupMetadata) mgm;
-			return messageGroupMetadata.size();
+			return mgm.size();
+		}
+		else {
+			return 0;
 		}
-		return 0;
 	}
 
 	protected abstract Object doRetrieve(Object id);
@@ -308,48 +344,6 @@ public abstract class AbstractKeyValueMessageStore extends AbstractMessageGroupS
 		return enrichedMessage;
 	}
 
-	private MessageGroup buildMessageGroup(Object groupId, boolean raw) {
-		Assert.notNull(groupId, "'groupId' must not be null");
-		Object mgm = doRetrieve(MESSAGE_GROUP_KEY_PREFIX + groupId);
-		if (mgm != null) {
-			Assert.isInstanceOf(MessageGroupMetadata.class, mgm);
-			MessageGroupMetadata messageGroupMetadata = (MessageGroupMetadata) mgm;
-			ArrayList<Message<?>> messages = new ArrayList<Message<?>>();
-
-			Iterator<UUID> messageIds = messageGroupMetadata.messageIdIterator();
-			while (messageIds.hasNext()) {
-				UUID next = messageIds.next();
-				if (next != null) {
-					if (raw) {
-						messages.add(getRawMessage(next));
-					}
-					else {
-						messages.add(getMessage(next));
-					}
-				}
-			}
-
-			MessageGroup messageGroup = getMessageGroupFactory()
-					.create(messages, groupId, messageGroupMetadata.getTimestamp(), messageGroupMetadata.isComplete());
-			messageGroup.setLastModified(messageGroupMetadata.getLastModified());
-			messageGroup.setLastReleasedMessageSequenceNumber(
-					messageGroupMetadata.getLastReleasedMessageSequenceNumber());
-			return messageGroup;
-		}
-		else {
-			return getMessageGroupFactory().create(groupId);
-		}
-	}
-
-	private MessageGroup normalizeSimpleMessageGroup(MessageGroup messageGroup) {
-		MessageGroup normalizedGroup = getMessageGroupFactory().create(messageGroup.getGroupId());
-		for (Message<?> message : messageGroup.getMessages()) {
-			Message<?> normalizedMessage = normalizeMessage(message);
-			normalizedGroup.add(normalizedMessage);
-		}
-		return normalizedGroup;
-	}
-
 	private Message<?> getRawMessage(UUID id) {
 		Assert.notNull(id, "'id' must not be null");
 		Object message = doRetrieve(MESSAGE_KEY_PREFIX + id);
@@ -380,4 +374,5 @@ public abstract class AbstractKeyValueMessageStore extends AbstractMessageGroupS
 			throw new UnsupportedOperationException();
 		}
 	}
+
 }

spring-integration-core/src/main/java/org/springframework/integration/store/AbstractMessageGroupStore.java

@@ -49,6 +49,9 @@ public abstract class AbstractMessageGroupStore extends AbstractBatchingMessageG
 
 	private final Collection<MessageGroupCallback> expiryCallbacks = new LinkedHashSet<MessageGroupCallback>();
 
+	private final MessageGroupFactory persistentMessageGroupFactory =
+			new SimpleMessageGroupFactory(SimpleMessageGroupFactory.GroupType.PERSISTENT);
+
 	private volatile boolean timeoutOnIdle;
 
 	private volatile BeanFactory beanFactory;
@@ -57,6 +60,8 @@ public abstract class AbstractMessageGroupStore extends AbstractBatchingMessageG
 
 	private volatile boolean messageBuilderFactorySet;
 
+	private boolean lazyLoadMessageGroups = true;
+
 	public AbstractMessageGroupStore() {
 		super();
 	}
@@ -77,6 +82,16 @@ public abstract class AbstractMessageGroupStore extends AbstractBatchingMessageG
 		return this.messageBuilderFactory;
 	}
 
+	@Override
+	protected MessageGroupFactory getMessageGroupFactory() {
+		if (this.lazyLoadMessageGroups) {
+			return this.persistentMessageGroupFactory;
+		}
+		else {
+			return super.getMessageGroupFactory();
+		}
+	}
+
 	/**
 	 * Convenient injection point for expiry callbacks in the message store. Each of the callbacks provided will simply
 	 * be registered with the store using {@link #registerMessageGroupExpiryCallback(MessageGroupCallback)}.
@@ -98,13 +113,24 @@ public abstract class AbstractMessageGroupStore extends AbstractBatchingMessageG
 	 * the {@link MessageGroup} was created. If you want the timeout to be based on the time
 	 * the {@link MessageGroup} was idling (e.g., inactive from the last update) invoke this method with 'true'.
 	 * Default is 'false'.
-	 *
 	 * @param timeoutOnIdle The boolean.
 	 */
 	public void setTimeoutOnIdle(boolean timeoutOnIdle) {
 		this.timeoutOnIdle = timeoutOnIdle;
 	}
 
+	/**
+	 * Specify if the result of the {@link #getMessageGroup(Object)} should be wrapped
+	 * to the {@link PersistentMessageGroup} - a lazy-load proxy for messages in group
+	 * Defaults to {@code true}.
+	 * <p> The target logic is based on the {@link SimpleMessageGroupFactory.GroupType#PERSISTENT}.
+	 * @param lazyLoadMessageGroups the {@code boolean} flag to use.
+	 * @since 4.3
+	 */
+	public void setLazyLoadMessageGroups(boolean lazyLoadMessageGroups) {
+		this.lazyLoadMessageGroups = lazyLoadMessageGroups;
+	}
+
 	@Override
 	public void registerMessageGroupExpiryCallback(MessageGroupCallback callback) {
 		this.expiryCallbacks.add(callback);
@@ -119,7 +145,7 @@ public abstract class AbstractMessageGroupStore extends AbstractBatchingMessageG
 
 			long timestamp = group.getTimestamp();
 			if (this.isTimeoutOnIdle() && group.getLastModified() > 0) {
-			    timestamp = group.getLastModified();
+				timestamp = group.getLastModified();
 			}
 
 			if (timestamp <= threshold) {
@@ -175,8 +201,9 @@ public abstract class AbstractMessageGroupStore extends AbstractBatchingMessageG
 	}
 
 	@Override
-	public Message<?> getOneMessageFromGroup(Object groupId) {
-		throw new UnsupportedOperationException("Not yet implemented for this store");
+	public MessageGroup addMessageToGroup(Object groupId, Message<?> message) {
+		addMessagesToGroup(groupId, message);
+		return getMessageGroup(groupId);
 	}
 
 	private void expire(MessageGroup group) {

spring-integration-core/src/main/java/org/springframework/integration/store/MessageGroupFactory.java

@@ -29,11 +29,57 @@ import org.springframework.messaging.Message;
  */
 public interface MessageGroupFactory {
 
+	/**
+	 * Create a {@link MessageGroup} instance based on the provided {@code groupId}.
+	 * @param groupId the group id to use.
+	 * @return the {@link MessageGroup} instance.
+	 */
 	MessageGroup create(Object groupId);
 
+	/**
+	 * Create a {@link MessageGroup} instance based on the provided {@code groupId}
+	 * and with the {@code messages} for the group.
+	 * @param messages the messages for the group.
+	 * @param groupId the group id to use.
+	 * @return the {@link MessageGroup} instance.
+	 */
 	MessageGroup create(Collection<? extends Message<?>> messages, Object groupId);
 
+	/**
+	 * Create a {@link MessageGroup} instance based on the provided {@code groupId}
+	 * and with the {@code messages} for the group.
+	 * In addition the creating {@code timestamp} and {@code complete} flag may be used to customize
+	 * the target {@link MessageGroup} object.
+	 * @param messages the messages for the group.
+	 * @param groupId the group id to use.
+	 * @param timestamp the creation time.
+	 * @param complete the {@code boolean} flag to indicate that group is completed.
+	 * @return the {@link MessageGroup} instance.
+	 */
 	MessageGroup create(Collection<? extends Message<?>> messages, Object groupId, long timestamp,
 						boolean complete);
 
+	/**
+	 * Create a {@link MessageGroup} instance based on the provided {@code groupId}.
+	 * The {@link MessageGroupStore} may be consulted for the messages and metadata for the {@link MessageGroup}.
+	 * @param messageGroupStore the {@link MessageGroupStore} for additional {@link MessageGroup} information.
+	 * @param groupId the group id to use.
+	 * @return the {@link MessageGroup} instance.
+	 */
+	MessageGroup create(MessageGroupStore messageGroupStore, Object groupId);
+
+	/**
+	 * Create a {@link MessageGroup} instance based on the provided {@code groupId}.
+	 * The {@link MessageGroupStore} may be consulted for the messages and metadata for the {@link MessageGroup}.
+	 * In addition the creating {@code timestamp} and {@code complete} flag may be used to customize
+	 * the target {@link MessageGroup} object.
+	 * @param messageGroupStore the {@link MessageGroupStore} for additional {@link MessageGroup} information.
+	 * @param groupId the group id to use.
+	 * @param timestamp the creation time.
+	 * @param complete the {@code boolean} flag to indicate that group is completed.
+	 * @return the {@link MessageGroup} instance.
+	 */
+	MessageGroup create(MessageGroupStore messageGroupStore, Object groupId, long timestamp,
+			boolean complete);
+
 }

spring-integration-core/src/main/java/org/springframework/integration/store/MessageGroupMetadata.java

@@ -26,10 +26,11 @@ import org.springframework.messaging.Message;
 import org.springframework.util.Assert;
 
 /**
- * Immutable Value Object holding metadata about a MessageGroup.
+ * Value Object holding metadata about a MessageGroup in the MessageGroupStore.
  *
  * @author Oleg Zhurakousky
  * @author Gary Russell
+ * @author Artem Bilan
  * @since 2.1
  */
 public class MessageGroupMetadata implements Serializable {
@@ -40,47 +41,35 @@ public class MessageGroupMetadata implements Serializable {
 
 	private final List<UUID> messageIds = new LinkedList<UUID>();
 
-	private final boolean complete;
-
 	private final long timestamp;
 
+	private volatile boolean complete;
+
 	private volatile long lastModified;
 
-	private final int lastReleasedMessageSequenceNumber;
-
-	private final boolean hasMessages;
-
-	private final UUID first;
+	private volatile int lastReleasedMessageSequenceNumber;
 
 	public MessageGroupMetadata(MessageGroup messageGroup) {
-		this(messageGroup, true, null);
-	}
-
-	public MessageGroupMetadata(MessageGroup messageGroup, boolean hasMessages, UUID first) {
-
 		Assert.notNull(messageGroup, "'messageGroup' must not be null");
 		this.groupId = messageGroup.getGroupId();
-		if (hasMessages) {
-			for (Message<?> message : messageGroup.getMessages()) {
-				this.messageIds.add(message.getHeaders().getId());
-			}
+		for (Message<?> message : messageGroup.getMessages()) {
+			this.messageIds.add(message.getHeaders().getId());
 		}
 		this.complete = messageGroup.isComplete();
 		this.timestamp = messageGroup.getTimestamp();
 		this.lastReleasedMessageSequenceNumber = messageGroup.getLastReleasedMessageSequenceNumber();
 		this.lastModified = messageGroup.getLastModified();
-		this.hasMessages = hasMessages;
-		this.first = first;
 	}
 
 	public void remove(UUID messageId) {
-		if (!this.hasMessages) {
-			throw new IllegalStateException("Messages are not available, fetch the entire group");
-		}
 		this.messageIds.remove(messageId);
 	}
 
-	public void setLastModified(long lastModified) {
+	boolean add(UUID messageId) {
+		return !this.messageIds.contains(messageId) && this.messageIds.add(messageId);
+	}
+
+	void setLastModified(long lastModified) {
 		this.lastModified = lastModified;
 	}
 
@@ -89,9 +78,6 @@ public class MessageGroupMetadata implements Serializable {
 	}
 
 	public Iterator<UUID> messageIdIterator() {
-		if (!this.hasMessages) {
-			throw new IllegalStateException("Messages are not available, fetch the entire group");
-		}
 		return this.messageIds.iterator();
 	}
 
@@ -100,18 +86,16 @@ public class MessageGroupMetadata implements Serializable {
 	}
 
 	public UUID firstId() {
-		if (this.first != null) {
-			return this.first;
-		}
-		if (!this.hasMessages) {
-			throw new IllegalStateException("Messages are not available, fetch the entire group");
-		}
 		if (this.messageIds.size() > 0) {
-			return this.messageIds.iterator().next();
+			return this.messageIds.get(0);
 		}
 		return null;
 	}
 
+	void complete() {
+		this.complete = true;
+	}
+
 	public boolean isComplete() {
 		return this.complete;
 	}
@@ -127,4 +111,9 @@ public class MessageGroupMetadata implements Serializable {
 	public int getLastReleasedMessageSequenceNumber() {
 		return this.lastReleasedMessageSequenceNumber;
 	}
+
+	void setLastReleasedMessageSequenceNumber(int lastReleasedMessageSequenceNumber) {
+		this.lastReleasedMessageSequenceNumber = lastReleasedMessageSequenceNumber;
+	}
+
 }

spring-integration-core/src/main/java/org/springframework/integration/store/MessageGroupStore.java

@@ -29,6 +29,7 @@ import org.springframework.messaging.Message;
  * @author Dave Syer
  * @author Oleg Zhurakousky
  * @author Gary Russell
+ * @author Artem Bilan
  *
  * @since 2.0
  *
@@ -36,9 +37,8 @@ import org.springframework.messaging.Message;
 public interface MessageGroupStore extends BasicMessageGroupStore {
 
 	/**
-	 * Optional attribute giving the number of messages in the store over all groups. Implementations may decline to
-	 * respond by throwing an exception.
-	 *
+	 * Optional attribute giving the number of messages in the store over all groups.
+	 * Implementations may decline to respond by throwing an exception.
 	 * @return the number of messages
 	 * @throws UnsupportedOperationException if not implemented
 	 */
@@ -46,9 +46,8 @@ public interface MessageGroupStore extends BasicMessageGroupStore {
 	int getMessageCountForAllMessageGroups();
 
 	/**
-	 * Optional attribute giving the number of  message groups. Implementations may decline
-	 * to respond by throwing an exception.
-	 *
+	 * Optional attribute giving the number of  message groups.
+	 * Implementations may decline to respond by throwing an exception.
 	 * @return the number message groups
 	 * @throws UnsupportedOperationException if not implemented
 	 */
@@ -56,9 +55,8 @@ public interface MessageGroupStore extends BasicMessageGroupStore {
 	int getMessageGroupCount();
 
 	/**
-	 * Persist the deletion of a single message from the group. The group is modified to reflect that 'messageToRemove' is
-	 * no longer present in the group.
-	 *
+	 * Persist the deletion of a single message from the group.
+	 * The group is modified to reflect that 'messageToRemove' is no longer present in the group.
 	 * @param key The groupId for the group containing the message.
 	 * @param messageToRemove The message to be removed.
 	 * @return The message Group.
@@ -69,27 +67,22 @@ public interface MessageGroupStore extends BasicMessageGroupStore {
 
 	/**
 	 * Persist the deletion of messages from the group.
-	 *
 	 * @param key The groupId for the group containing the message(s).
 	 * @param messages The messages to be removed.
-	 *
 	 * @since 4.2
 	 */
 	void removeMessagesFromGroup(Object key, Collection<Message<?>> messages);
 
 	/**
 	 * Persist the deletion of messages from the group.
-	 *
 	 * @param key The groupId for the group containing the message(s).
 	 * @param messages The messages to be removed.
-	 *
 	 * @since 4.2
 	 */
 	void removeMessagesFromGroup(Object key, Message<?>... messages);
 
 	/**
 	 * Register a callback for when a message group is expired through {@link #expireMessageGroups(long)}.
-	 *
 	 * @param callback A callback to execute when a message group is cleaned up.
 	 */
 	void registerMessageGroupExpiryCallback(MessageGroupCallback callback);
@@ -99,10 +92,8 @@ public interface MessageGroupStore extends BasicMessageGroupStore {
 	 * each of the registered callbacks on them in turn. For example: call with a timeout of 100 to expire all groups
 	 * that were created more than 100 milliseconds ago, and are not yet complete. Use a timeout of 0 (or negative to be
 	 * on the safe side) to expire all message groups.
-	 *
 	 * @param timeout the timeout threshold to use
 	 * @return the number of message groups expired
-	 *
 	 * @see #registerMessageGroupExpiryCallback(MessageGroupCallback)
 	 */
 	@ManagedOperation
@@ -110,7 +101,6 @@ public interface MessageGroupStore extends BasicMessageGroupStore {
 
 	/**
 	 * Allows you to set the sequence number of the last released Message. Used for Resequencing use cases
-	 *
 	 * @param groupId The group identifier.
 	 * @param sequenceNumber The sequence number.
 	 */
@@ -125,7 +115,6 @@ public interface MessageGroupStore extends BasicMessageGroupStore {
 	 * Completes this MessageGroup. Completion of the MessageGroup generally means
 	 * that this group should not be allowing any more mutating operation to be performed on it.
 	 * For example any attempt to add/remove new Message form the group should not be allowed.
-	 *
 	 * @param groupId The group identifier.
 	 */
 	void completeGroup(Object groupId);
@@ -140,13 +129,30 @@ public interface MessageGroupStore extends BasicMessageGroupStore {
 	MessageGroupMetadata getGroupMetadata(Object groupId);
 
 	/**
-	 * Return the one {@link org.springframework.messaging.Message} from {@link org.springframework.integration.store.MessageGroup}.
+	 * Return the one {@link Message} from {@link MessageGroup}.
 	 * @param groupId The group identifier.
-	 * @return the {@link org.springframework.messaging.Message}.
+	 * @return the {@link Message}.
 	 * @since 4.0
 	 */
 	Message<?> getOneMessageFromGroup(Object groupId);
 
+	/**
+	 * Store messages with an association to a group id.
+	 * This can be used to group messages together.
+	 * @param groupId The group id to store messages under.
+	 * @param messages The messages to add.
+	 * @since 4.3
+	 */
+	void addMessagesToGroup(Object groupId, Message<?>... messages);
+
+	/**
+	 * Retrieve messages for the provided group id.
+	 * @param groupId The group id to retrieve messages for.
+	 * @return the messages for group.
+	 * @since 4.3
+	 */
+	Collection<Message<?>> getMessagesForGroup(Object groupId);
+
 	/**
 	 * Invoked when a MessageGroupStore expires a group.
 	 */

spring-integration-core/src/main/java/org/springframework/integration/store/PersistentMessageGroup.java

@@ -0,0 +1,226 @@
+/*
+ * Copyright 2016 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.store;
+
+import java.util.AbstractCollection;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Iterator;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import org.springframework.integration.IntegrationMessageHeaderAccessor;
+import org.springframework.messaging.Message;
+
+/**
+ * @author Artem Bilan
+ * @since 4.3
+ */
+class PersistentMessageGroup implements MessageGroup {
+
+	private static final Log logger = LogFactory.getLog(PersistentMessageGroup.class);
+
+	private MessageGroupStore messageGroupStore;
+
+	private final Collection<Message<?>> messages = new PersistentCollection();
+
+	private final MessageGroup original;
+
+	private volatile Message<?> oneMessage;
+
+	private volatile int size;
+
+	PersistentMessageGroup(MessageGroupStore messageGroupStore, MessageGroup original) {
+		this.messageGroupStore = messageGroupStore;
+		this.original = original;
+	}
+
+	public void setSize(int size) {
+		this.size = size;
+	}
+
+	@Override
+	public Collection<Message<?>> getMessages() {
+		return Collections.unmodifiableCollection(this.messages);
+	}
+
+	@Override
+	public Message<?> getOne() {
+		if (this.oneMessage == null) {
+			synchronized (this) {
+				if (this.oneMessage == null) {
+					if (logger.isDebugEnabled()) {
+						logger.debug("Lazy loading of one message for messageGroup: " + this.original.getGroupId());
+					}
+					this.oneMessage = this.messageGroupStore.getOneMessageFromGroup(this.original.getGroupId());
+				}
+			}
+		}
+		return this.oneMessage;
+	}
+
+	@Override
+	public int getSequenceSize() {
+		if (size() == 0) {
+			return 0;
+		}
+		else {
+			Message<?> message = getOne();
+			if (message != null) {
+				Integer sequenceSize = message.getHeaders()
+						.get(IntegrationMessageHeaderAccessor.SEQUENCE_SIZE, Integer.class);
+				return (sequenceSize != null ? sequenceSize : 0);
+			}
+			else {
+				return 0;
+			}
+		}
+	}
+
+	@Override
+	public int size() {
+		if (this.size == 0) {
+			synchronized (this) {
+				if (this.size == 0) {
+					if (logger.isDebugEnabled()) {
+						logger.debug("Lazy loading of group size for messageGroup: " + this.original.getGroupId());
+					}
+					this.size = this.messageGroupStore.messageGroupSize(this.original.getGroupId());
+				}
+			}
+		}
+		return this.size;
+	}
+
+	@Override
+	public Object getGroupId() {
+		return this.original.getGroupId();
+	}
+
+	@Override
+	public boolean canAdd(Message<?> message) {
+		return this.original.canAdd(message);
+	}
+
+	@Override
+	public int getLastReleasedMessageSequenceNumber() {
+		return this.original.getLastReleasedMessageSequenceNumber();
+	}
+
+	@Override
+	public boolean isComplete() {
+		return this.original.isComplete();
+	}
+
+	@Override
+	public void complete() {
+		this.original.complete();
+	}
+
+	@Override
+	public long getTimestamp() {
+		return this.original.getTimestamp();
+	}
+
+	@Override
+	public long getLastModified() {
+		return this.original.getLastModified();
+	}
+
+	@Override
+	public void setLastModified(long lastModified) {
+		this.original.setLastModified(lastModified);
+	}
+
+	@Override
+	public void add(Message<?> messageToAdd) {
+		this.original.add(messageToAdd);
+	}
+
+	@Override
+	public boolean remove(Message<?> messageToRemove) {
+		return this.original.remove(messageToRemove);
+	}
+
+	@Override
+	public void setLastReleasedMessageSequenceNumber(int sequenceNumber) {
+		this.original.setLastReleasedMessageSequenceNumber(sequenceNumber);
+	}
+
+	@Override
+	public void clear() {
+		this.original.clear();
+	}
+
+
+	private class PersistentCollection extends AbstractCollection<Message<?>> {
+
+		private volatile Collection<Message<?>> collection;
+
+		private void load() {
+			if (this.collection == null) {
+				synchronized (this) {
+					if (this.collection == null) {
+						Object groupId = PersistentMessageGroup.this.original.getGroupId();
+						if (logger.isDebugEnabled()) {
+							logger.debug("Lazy loading of messages for messageGroup: " + groupId);
+						}
+						this.collection = PersistentMessageGroup.this.messageGroupStore.getMessagesForGroup(groupId);
+					}
+				}
+			}
+		}
+
+		@Override
+		public boolean contains(Object o) {
+			load();
+			return this.collection.contains(o);
+		}
+
+		@Override
+		public Object[] toArray() {
+			load();
+			return this.collection.toArray();
+		}
+
+		@Override
+		public <T> T[] toArray(T[] a) {
+			load();
+			return this.collection.toArray(a);
+		}
+
+		@Override
+		public boolean containsAll(Collection<?> c) {
+			load();
+			return this.collection.containsAll(c);
+		}
+
+		@Override
+		public Iterator<Message<?>> iterator() {
+			load();
+			return this.collection.iterator();
+		}
+
+		@Override
+		public int size() {
+			return PersistentMessageGroup.this.size();
+		}
+
+	}
+
+}

spring-integration-core/src/main/java/org/springframework/integration/store/SimpleMessageGroupFactory.java

@@ -59,6 +59,28 @@ public class SimpleMessageGroupFactory implements MessageGroupFactory {
 		return new SimpleMessageGroup(this.type.get(), messages, groupId, timestamp, complete);
 	}
 
+	@Override
+	public MessageGroup create(MessageGroupStore messageGroupStore, Object groupId) {
+		if (GroupType.PERSISTENT.equals(this.type)) {
+			return new PersistentMessageGroup(messageGroupStore, new SimpleMessageGroup(groupId));
+		}
+		else {
+			return create(messageGroupStore.getMessagesForGroup(groupId), groupId);
+		}
+	}
+
+	@Override
+	public MessageGroup create(MessageGroupStore messageGroupStore, Object groupId, long timestamp, boolean complete) {
+		if (GroupType.PERSISTENT.equals(this.type)) {
+			SimpleMessageGroup original = new SimpleMessageGroup(Collections.<Message<?>>emptyList(), groupId,
+					timestamp, complete);
+			return new PersistentMessageGroup(messageGroupStore, original);
+		}
+		else {
+			return create(messageGroupStore.getMessagesForGroup(groupId), groupId, timestamp, complete);
+		}
+	}
+
 	public enum GroupType {
 
 		BLOCKING_QUEUE {
@@ -84,6 +106,14 @@ public class SimpleMessageGroupFactory implements MessageGroupFactory {
 				return Collections.<Message<?>>synchronizedSet(new LinkedHashSet<Message<?>>());
 			}
 
+		},
+		PERSISTENT {
+
+			@Override
+			Collection<Message<?>> get() {
+				return HASH_SET.get();
+			}
+
 		};
 
 		abstract Collection<Message<?>> get();

spring-integration-core/src/main/java/org/springframework/integration/store/SimpleMessageStore.java

@@ -239,7 +239,10 @@ public class SimpleMessageStore extends AbstractMessageGroupStore
 	}
 
 	@Override
-	public MessageGroup addMessageToGroup(Object groupId, Message<?> message) {
+	public void addMessagesToGroup(Object groupId, Message<?>... messages) {
+		Assert.notNull(groupId, "'groupId' must not be null");
+		Assert.notNull(messages, "'messages' must not be null");
+
 		Lock lock = this.lockRegistry.obtain(groupId);
 		try {
 			lock.lockInterruptibly();
@@ -247,31 +250,38 @@ public class SimpleMessageStore extends AbstractMessageGroupStore
 			try {
 				UpperBound upperBound;
 				MessageGroup group = this.groupIdToMessageGroup.get(groupId);
+				MessagingException outOfCapacityException =
+						new MessagingException(getClass().getSimpleName() +
+								" was out of capacity (" + this.groupCapacity + ") for group '" + groupId +
+								"', try constructing it with a larger capacity.");
 				if (group == null) {
+					if (this.groupCapacity > 0 && messages.length > this.groupCapacity) {
+						throw outOfCapacityException;
+					}
 					group = getMessageGroupFactory().create(groupId);
 					this.groupIdToMessageGroup.putIfAbsent(groupId, group);
 					upperBound = new UpperBound(this.groupCapacity);
-					upperBound.tryAcquire(-1);
+					for (Message<?> message : messages) {
+						upperBound.tryAcquire(-1);
+						group.add(message);
+					}
 					this.groupToUpperBound.putIfAbsent(groupId, upperBound);
 				}
 				else {
 					upperBound = this.groupToUpperBound.get(groupId);
 					Assert.state(upperBound != null, "'upperBound' must not be null.");
-					lock.unlock();
-					if (!upperBound.tryAcquire(this.upperBoundTimeout)) {
-						unlocked = true;
-						throw new MessagingException(this.getClass().getSimpleName()
-								+ " was out of capacity ("
-								+ this.groupCapacity
-								+ ") for group '"
-								+ groupId
-								+ "', try constructing it with a larger capacity.");
+					for (Message<?> message : messages) {
+						lock.unlock();
+						if (!upperBound.tryAcquire(this.upperBoundTimeout)) {
+							unlocked = true;
+							throw outOfCapacityException;
+						}
+						lock.lockInterruptibly();
+						group.add(message);
 					}
-					lock.lockInterruptibly();
 				}
-				group.add(message);
+
 				group.setLastModified(System.currentTimeMillis());
-				return group;
 			}
 			finally {
 				if (!unlocked) {
@@ -445,6 +455,11 @@ public class SimpleMessageStore extends AbstractMessageGroupStore
 		return getMessageGroup(groupId).getOne();
 	}
 
+	@Override
+	public Collection<Message<?>> getMessagesForGroup(Object groupId) {
+		return getMessageGroup(groupId).getMessages();
+	}
+
 	public void clearMessageGroup(Object groupId) {
 		Lock lock = this.lockRegistry.obtain(groupId);
 		try {

spring-integration-core/src/test/java/org/springframework/integration/aggregator/AbstractCorrelatingMessageHandlerTests.java

@@ -293,9 +293,8 @@ public class AbstractCorrelatingMessageHandlerTests {
 		Method forceComplete =
 				AbstractCorrelatingMessageHandler.class.getDeclaredMethod("forceComplete", MessageGroup.class);
 		forceComplete.setAccessible(true);
-		mgs.addMessageToGroup("foo", new GenericMessage<String>("foo"));
 		GenericMessage<String> secondMessage = new GenericMessage<String>("bar");
-		mgs.addMessageToGroup("foo", secondMessage);
+		mgs.addMessagesToGroup("foo", new GenericMessage<String>("foo"), secondMessage);
 		MessageGroup group = mgs.getMessageGroup("foo");
 		// remove a message
 		mgs.removeMessagesFromGroup("foo", secondMessage);
@@ -324,7 +323,7 @@ public class AbstractCorrelatingMessageHandlerTests {
 		QueueChannel outputChannel = new QueueChannel();
 		handler.setOutputChannel(outputChannel);
 		MessageGroupStore mgs = TestUtils.getPropertyValue(handler, "messageStore", MessageGroupStore.class);
-		mgs.addMessageToGroup("foo", new GenericMessage<String>("foo"));
+		mgs.addMessagesToGroup("foo", new GenericMessage<String>("foo"));
 		mgs.completeGroup("foo");
 		mgs = spy(mgs);
 		new DirectFieldAccessor(handler).setPropertyValue("messageStore", mgs);
@@ -357,7 +356,7 @@ public class AbstractCorrelatingMessageHandlerTests {
 		QueueChannel outputChannel = new QueueChannel();
 		handler.setOutputChannel(outputChannel);
 		MessageGroupStore mgs = TestUtils.getPropertyValue(handler, "messageStore", MessageGroupStore.class);
-		mgs.addMessageToGroup("foo", new GenericMessage<String>("foo"));
+		mgs.addMessagesToGroup("foo", new GenericMessage<String>("foo"));
 		MessageGroup group = new SimpleMessageGroup(mgs.getMessageGroup("foo"));
 		mgs.completeGroup("foo");
 		mgs = spy(mgs);
@@ -393,7 +392,7 @@ public class AbstractCorrelatingMessageHandlerTests {
 		QueueChannel outputChannel = new QueueChannel();
 		handler.setOutputChannel(outputChannel);
 		MessageGroupStore mgs = TestUtils.getPropertyValue(handler, "messageStore", MessageGroupStore.class);
-		mgs.addMessageToGroup("foo", new GenericMessage<String>("foo"));
+		mgs.addMessagesToGroup("foo", new GenericMessage<String>("foo"));
 		MessageGroup group = new SimpleMessageGroup(mgs.getMessageGroup("foo"));
 		mgs = spy(mgs);
 		new DirectFieldAccessor(handler).setPropertyValue("messageStore", mgs);

spring-integration-core/src/test/java/org/springframework/integration/config/xml/GatewayParserTests.java

@@ -36,7 +36,6 @@ import java.util.concurrent.atomic.AtomicReference;
 import org.apache.commons.logging.Log;
 import org.junit.Test;
 import org.junit.runner.RunWith;
-import reactor.rx.Promise;
 
 import org.springframework.beans.DirectFieldAccessor;
 import org.springframework.beans.factory.BeanNameAware;
@@ -65,6 +64,8 @@ import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
 
+import reactor.rx.Promise;
+
 /**
  * @author Mark Fisher
  * @author Artem Bilan
@@ -173,7 +174,7 @@ public class GatewayParserTests {
 		this.startResponder(requestChannel, replyChannel);
 		TestService service = context.getBean("promise", TestService.class);
 		Promise<Message<?>> result = service.promise("foo");
-		Message<?> reply = result.await(1, TimeUnit.SECONDS);
+		Message<?> reply = result.await(10, TimeUnit.SECONDS);
 		assertEquals("foo", reply.getPayload());
 		assertNotNull(TestUtils.getPropertyValue(context.getBean("&promise"), "asyncExecutor"));
 	}

spring-integration-core/src/test/java/org/springframework/integration/store/MessageStoreTests.java

@@ -34,6 +34,7 @@ import org.springframework.test.util.ReflectionTestUtils;
 /**
  * @author Dave Syer
  * @author Gary Russell
+ * @author Artem Bilan
  */
 public class MessageStoreTests {
 
@@ -80,7 +81,7 @@ public class MessageStoreTests {
 		assertEquals(1, store.getMessageCountForAllMessageGroups());
 	}
 
-	private static class TestMessageStore extends AbstractMessageGroupStore {
+	private static class TestMessageStore extends SimpleMessageStore  {
 
 		@SuppressWarnings("unchecked")
 		MessageGroup testMessages =
@@ -95,7 +96,7 @@ public class MessageStoreTests {
 		}
 
 		@Override
-		public MessageGroup addMessageToGroup(Object correlationKey, Message<?> message) {
+		public void addMessagesToGroup(Object groupId, Message<?>... messages) {
 			throw new UnsupportedOperationException();
 		}