001 /**
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.camel.processor.loadbalancer;
018
019 import java.util.HashMap;
020 import java.util.Iterator;
021 import java.util.List;
022 import java.util.Map;
023
024 import org.apache.camel.Exchange;
025 import org.apache.camel.Expression;
026 import org.apache.camel.Processor;
027
028 /**
029 * Implements a sticky load balancer using an {@link Expression} to calculate
030 * a correlation key to perform the sticky load balancing; rather like jsessionid in the web
031 * or JMSXGroupID in JMS.
032 *
033 * @version $Revision: 709613 $
034 */
035 public class StickyLoadBalancer extends QueueLoadBalancer {
036 private Expression correlationExpression;
037 private QueueLoadBalancer loadBalancer;
038 private int numberOfHashGroups = 64 * 1024;
039 private final Map<Object, Processor> stickyMap = new HashMap<Object, Processor>();
040
041 public StickyLoadBalancer() {
042 this.loadBalancer = new RoundRobinLoadBalancer();
043 }
044
045 public StickyLoadBalancer(Expression correlationExpression) {
046 this(correlationExpression, new RoundRobinLoadBalancer());
047 }
048
049 public StickyLoadBalancer(Expression correlationExpression, QueueLoadBalancer loadBalancer) {
050 this.correlationExpression = correlationExpression;
051 this.loadBalancer = loadBalancer;
052 }
053
054 public void setCorrelationExpression(Expression correlationExpression) {
055 this.correlationExpression = correlationExpression;
056 }
057
058 public void setLoadBalancer(QueueLoadBalancer loadBalancer) {
059 this.loadBalancer = loadBalancer;
060 }
061
062 protected synchronized Processor chooseProcessor(List<Processor> processors, Exchange exchange) {
063 Object value = correlationExpression.evaluate(exchange);
064 Object key = getStickyKey(value);
065
066 Processor processor;
067 synchronized (stickyMap) {
068 processor = stickyMap.get(key);
069 if (processor == null) {
070 processor = loadBalancer.chooseProcessor(processors, exchange);
071 stickyMap.put(key, processor);
072 }
073 }
074 return processor;
075 }
076
077 @Override
078 public void removeProcessor(Processor processor) {
079 synchronized (stickyMap) {
080 Iterator<Map.Entry<Object, Processor>> iter = stickyMap.entrySet().iterator();
081 while (iter.hasNext()) {
082 Map.Entry<Object, Processor> entry = iter.next();
083 if (processor.equals(entry.getValue())) {
084 iter.remove();
085 }
086 }
087 }
088 super.removeProcessor(processor);
089 }
090
091
092 // Properties
093 //-------------------------------------------------------------------------
094 public int getNumberOfHashGroups() {
095 return numberOfHashGroups;
096 }
097
098 public void setNumberOfHashGroups(int numberOfHashGroups) {
099 this.numberOfHashGroups = numberOfHashGroups;
100 }
101
102 // Implementation methods
103 //-------------------------------------------------------------------------
104
105 /**
106 * A strategy to create the key for the sticky load balancing map.
107 * The default implementation uses the hash code of the value
108 * then modulos by the numberOfHashGroups to avoid the sticky map getting too big
109 *
110 * @param value the correlation value
111 * @return the key to be used in the sticky map
112 */
113 protected Object getStickyKey(Object value) {
114 int hashCode = 37;
115 if (value != null) {
116 hashCode = value.hashCode();
117 }
118 if (numberOfHashGroups > 0) {
119 hashCode = hashCode % numberOfHashGroups;
120 }
121 return hashCode;
122 }
123 }