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: 1.1 $
034     */
035    public class StickyLoadBalancer extends QueueLoadBalancer {
036        private Expression<Exchange> correlationExpression;
037        private QueueLoadBalancer loadBalancer;
038        private int numberOfHashGroups = 64 * 1024;
039        private Map<Object, Processor> stickyMap = new HashMap<Object, Processor>();
040    
041        public StickyLoadBalancer(Expression<Exchange> correlationExpression) {
042            this(correlationExpression, new RoundRobinLoadBalancer());
043        }
044    
045        public StickyLoadBalancer(Expression<Exchange> correlationExpression, QueueLoadBalancer loadBalancer) {
046            this.correlationExpression = correlationExpression;
047            this.loadBalancer = loadBalancer;
048        }
049    
050        protected synchronized Processor chooseProcessor(List<Processor> processors, Exchange exchange) {
051            Object value = correlationExpression.evaluate(exchange);
052            Object key = getStickyKey(value);
053    
054            Processor processor;
055            synchronized (stickyMap) {
056                processor = stickyMap.get(key);
057                if (processor == null) {
058                    processor = loadBalancer.chooseProcessor(processors, exchange);
059                    stickyMap.put(key, processor);
060                }
061            }
062            return processor;
063        }
064    
065        @Override
066        public void removeProcessor(Processor processor) {
067            synchronized (stickyMap) {
068                Iterator<Map.Entry<Object, Processor>> iter = stickyMap.entrySet().iterator();
069                while (iter.hasNext()) {
070                    Map.Entry<Object, Processor> entry = iter.next();
071                    if (processor.equals(entry.getValue())) {
072                        iter.remove();
073                    }
074                }
075            }
076            super.removeProcessor(processor);
077        }
078    
079    
080        // Properties
081        //-------------------------------------------------------------------------
082        public int getNumberOfHashGroups() {
083            return numberOfHashGroups;
084        }
085    
086        public void setNumberOfHashGroups(int numberOfHashGroups) {
087            this.numberOfHashGroups = numberOfHashGroups;
088        }
089    
090        // Implementation methods
091        //-------------------------------------------------------------------------
092    
093        /**
094         * A strategy to create the key for the sticky load balancing map.
095         * The default implementation uses the hash code of the value
096         * then modulos by the numberOfHashGroups to avoid the sticky map getting too big
097         *
098         * @param value the correlation value
099         * @return the key to be used in the sticky map
100         */
101        protected Object getStickyKey(Object value) {
102            int hashCode = 37;
103            if (value != null) {
104                hashCode = value.hashCode();
105            }
106            if (numberOfHashGroups > 0) {
107                hashCode = hashCode % numberOfHashGroups;
108            }
109            return hashCode;
110        }
111    }