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: 795369 $
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 super();
043 this.loadBalancer = new RoundRobinLoadBalancer();
044 }
045
046 public StickyLoadBalancer(Expression correlationExpression) {
047 this(correlationExpression, new RoundRobinLoadBalancer());
048 }
049
050 public StickyLoadBalancer(Expression correlationExpression, QueueLoadBalancer loadBalancer) {
051 super();
052 this.correlationExpression = correlationExpression;
053 this.loadBalancer = loadBalancer;
054 }
055
056 protected synchronized Processor chooseProcessor(List<Processor> processors, Exchange exchange) {
057 Object value = correlationExpression.evaluate(exchange, Object.class);
058 Object key = getStickyKey(value);
059
060 Processor processor;
061 synchronized (stickyMap) {
062 processor = stickyMap.get(key);
063 if (processor == null) {
064 processor = loadBalancer.chooseProcessor(processors, exchange);
065 stickyMap.put(key, processor);
066 }
067 }
068 return processor;
069 }
070
071 @Override
072 public void removeProcessor(Processor processor) {
073 synchronized (stickyMap) {
074 Iterator<Map.Entry<Object, Processor>> iter = stickyMap.entrySet().iterator();
075 while (iter.hasNext()) {
076 Map.Entry<Object, Processor> entry = iter.next();
077 if (processor.equals(entry.getValue())) {
078 iter.remove();
079 }
080 }
081 }
082 super.removeProcessor(processor);
083 }
084
085
086 // Properties
087 //-------------------------------------------------------------------------
088 public int getNumberOfHashGroups() {
089 return numberOfHashGroups;
090 }
091
092 public void setNumberOfHashGroups(int numberOfHashGroups) {
093 this.numberOfHashGroups = numberOfHashGroups;
094 }
095
096 // Implementation methods
097 //-------------------------------------------------------------------------
098
099 /**
100 * A strategy to create the key for the sticky load balancing map.
101 * The default implementation uses the hash code of the value
102 * then modulos by the numberOfHashGroups to avoid the sticky map getting too big
103 *
104 * @param value the correlation value
105 * @return the key to be used in the sticky map
106 */
107 protected Object getStickyKey(Object value) {
108 int hashCode = 37;
109 if (value != null) {
110 hashCode = value.hashCode();
111 }
112 if (numberOfHashGroups > 0) {
113 hashCode = hashCode % numberOfHashGroups;
114 }
115 return hashCode;
116 }
117
118 public String toString() {
119 return "StickyLoadBalancer";
120 }
121
122 }