added an alternative eviction strategy

git-svn-id: https://svn.apache.org/repos/asf/incubator/activemq/trunk@382830 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -0,0 +1,48 @@
+/**
+ *
+ * Copyright 2005-2006 The Apache Software Foundation
+ *
+ * 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.apache.activemq.broker.region.policy;
+
+import org.apache.activemq.broker.region.MessageReference;
+
+import java.io.IOException;
+import java.util.Iterator;
+import java.util.LinkedList;
+
+/**
+ * An eviction strategy which evicts the oldest message with the lowest priority first.
+ * 
+ * @org.apache.xbean.XBean
+ * 
+ * @version $Revision$messageEvictionStrategy
+ */
+public class OldestMessageWithLowestPriorityEvictionStrategy implements MessageEvictionStrategy {
+
+    public MessageReference evictMessage(LinkedList messages) throws IOException {
+        byte lowestPriority = Byte.MAX_VALUE;
+        int pivot = 0;
+        Iterator iter = messages.iterator();
+        for (int i = 0; iter.hasNext(); i++) {
+            MessageReference reference = (MessageReference) iter.next();
+            byte priority = reference.getMessage().getPriority();
+            if (priority < lowestPriority) {
+                lowestPriority = priority;
+                pivot = i;
+            }
+        }
+        return (MessageReference) messages.remove(pivot);
+    }
+}