added a helper class and strategy method for people wishing to implement their own custom MessageQuery strategies to be fired as a new subscriber is created

git-svn-id: https://svn.apache.org/repos/asf/incubator/activemq/trunk@357712 13f79535-47bb-0310-9956-ffa450edef68

activemq-core/src/main/java/org/activemq/broker/region/policy/MessageQuery.java

@@ -0,0 +1,39 @@
+/**
+ * 
+ * Copyright 2005 LogicBlaze, Inc. http://www.logicblaze.com
+ * 
+ * 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.activemq.broker.region.policy;
+
+import org.activemq.command.ActiveMQDestination;
+
+import javax.jms.MessageListener;
+
+/**
+ * Represents some kind of query which will load messages from some source.
+ * 
+ * @version $Revision$
+ */
+public interface MessageQuery {
+    
+    /**
+     * Executes the query for messages; each message is passed into the listener
+     * 
+     * @param destination the destination on which the query is to be performed
+     * @param listener is the listener to notify as each message is created or loaded
+     */
+    public void execute(ActiveMQDestination destination, MessageListener listener);
+
+}

activemq-core/src/main/java/org/activemq/broker/region/policy/QueryBasedSubscriptionRecoveryPolicy.java

@@ -0,0 +1,101 @@
+/**
+ * <a href="http://activemq.org">ActiveMQ: The Open Source Message Fabric</a>
+ *
+ * Copyright 2005 (C) LogicBlaze, Inc. http://www.logicblaze.com
+ *
+ * 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.activemq.broker.region.policy;
+
+import org.activemq.ActiveMQMessageTransformation;
+import org.activemq.broker.ConnectionContext;
+import org.activemq.broker.region.MessageReference;
+import org.activemq.broker.region.Subscription;
+import org.activemq.command.ActiveMQDestination;
+import org.activemq.command.ActiveMQMessage;
+import org.activemq.filter.MessageEvaluationContext;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import javax.jms.Message;
+import javax.jms.MessageListener;
+
+/**
+ * This implementation of {@link SubscriptionRecoveryPolicy} will perform a user
+ * specific query mechanism to load any messages they may have missed.
+ * 
+ * @org.xbean.XBean
+ * 
+ * @version $Revision$
+ */
+public class QueryBasedSubscriptionRecoveryPolicy implements SubscriptionRecoveryPolicy {
+
+    private static final Log log = LogFactory.getLog(QueryBasedSubscriptionRecoveryPolicy.class);
+
+    private MessageQuery query;
+
+    public void add(ConnectionContext context, MessageReference message) throws Throwable {
+    }
+
+    public void recover(ConnectionContext context, final Subscription sub) throws Throwable {
+        if (query != null) {
+            final MessageEvaluationContext msgContext = context.getMessageEvaluationContext();
+            try {
+                ActiveMQDestination destination = sub.getConsumerInfo().getDestination();
+                query.execute(destination, new MessageListener() {
+                    public void onMessage(Message message) {
+                        dispatchInitialMessage(message, msgContext, sub);
+                    }
+                });
+            }
+            finally {
+                msgContext.clear();
+            }
+        }
+    }
+
+    public void start() throws Exception {
+        if (query != null) {
+            throw new IllegalArgumentException("No query property configured");
+        }
+    }
+
+    public void stop() throws Exception {
+    }
+
+    public MessageQuery getQuery() {
+        return query;
+    }
+
+    /**
+     * Sets the query strategy to load initial messages
+     */
+    public void setQuery(MessageQuery query) {
+        this.query = query;
+    }
+
+    protected void dispatchInitialMessage(Message message, MessageEvaluationContext msgContext, Subscription sub) {
+        try {
+            ActiveMQMessage activeMessage = ActiveMQMessageTransformation.transformMessage(message, null);
+            msgContext.setDestination(activeMessage.getDestination());
+            msgContext.setMessageReference(activeMessage);
+            if (sub.matches(activeMessage, msgContext)) {
+                sub.add(activeMessage);
+            }
+        }
+        catch (Throwable e) {
+            log.warn("Failed to dispatch initial message: " + message + " into subscription. Reason: " + e, e);
+        }
+    }
+}