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