001 /**
002 *
003 * Licensed to the Apache Software Foundation (ASF) under one or more
004 * contributor license agreements. See the NOTICE file distributed with
005 * this work for additional information regarding copyright ownership.
006 * The ASF licenses this file to You under the Apache License, Version 2.0
007 * (the "License"); you may not use this file except in compliance with
008 * the License. You may obtain a copy of the License at
009 *
010 * http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018 package org.apache.camel.processor.loadbalancer;
019
020 import org.apache.camel.Exchange;
021 import org.apache.camel.Expression;
022 import org.apache.camel.Processor;
023
024 import java.util.HashMap;
025 import java.util.List;
026 import java.util.Map;
027 import java.util.Set;
028 import java.util.Iterator;
029
030 /**
031 * Implements a sticky load balancer using an {@link Expression} to calculate
032 * a correlation key to perform the sticky load balancing; rather like jsessionid in the web
033 * or JMSXGroupID in JMS.
034 *
035 * @version $Revision: 1.1 $
036 */
037 public class StickyLoadBalancer extends QueueLoadBalancer {
038 private Expression<Exchange> correlationExpression;
039 private QueueLoadBalancer loadBalancer;
040 private int numberOfHashGroups = 64 * 1024;
041 private Map<Object, Processor> stickyMap = new HashMap<Object, Processor>();
042
043 public StickyLoadBalancer(Expression<Exchange> correlationExpression) {
044 this(correlationExpression, new RoundRobinLoadBalancer());
045 }
046
047 public StickyLoadBalancer(Expression<Exchange> correlationExpression, QueueLoadBalancer loadBalancer) {
048 this.correlationExpression = correlationExpression;
049 this.loadBalancer = loadBalancer;
050 }
051
052 protected synchronized Processor chooseProcessor(List<Processor> processors, Exchange exchange) {
053 Object value = correlationExpression.evaluate(exchange);
054 Object key = getStickyKey(value);
055
056 Processor processor;
057 synchronized (stickyMap) {
058 processor = stickyMap.get(key);
059 if (processor == null) {
060 processor = loadBalancer.chooseProcessor(processors, exchange);
061 stickyMap.put(key, processor);
062 }
063 }
064 return processor;
065 }
066
067 @Override
068 public void removeProcessor(Processor processor) {
069 synchronized (stickyMap) {
070 Iterator<Map.Entry<Object,Processor>> iter = stickyMap.entrySet().iterator();
071 while (iter.hasNext()) {
072 Map.Entry<Object, Processor> entry = iter.next();
073 if (processor.equals(entry.getValue())) {
074 iter.remove();
075 }
076 }
077 }
078 super.removeProcessor(processor);
079 }
080
081
082 // Properties
083 //-------------------------------------------------------------------------
084 public int getNumberOfHashGroups() {
085 return numberOfHashGroups;
086 }
087
088 public void setNumberOfHashGroups(int numberOfHashGroups) {
089 this.numberOfHashGroups = numberOfHashGroups;
090 }
091
092 // Implementation methods
093 //-------------------------------------------------------------------------
094
095 /**
096 * A strategy to create the key for the sticky load balancing map.
097 * The default implementation uses the hash code of the value
098 * then modulos by the numberOfHashGroups to avoid the sticky map getting too big
099 *
100 * @param value the correlation value
101 * @return the key to be used in the sticky map
102 */
103 protected Object getStickyKey(Object value) {
104 int hashCode = 37;
105 if (value != null) {
106 hashCode = value.hashCode();
107 }
108 if (numberOfHashGroups > 0) {
109 hashCode = hashCode % numberOfHashGroups;
110 }
111 return hashCode;
112 }
113 }