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: 36321 $ 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() { 042 this.loadBalancer = new RoundRobinLoadBalancer(); 043 } 044 045 public StickyLoadBalancer(Expression<Exchange> correlationExpression) { 046 this(correlationExpression, new RoundRobinLoadBalancer()); 047 } 048 049 public StickyLoadBalancer(Expression<Exchange> correlationExpression, QueueLoadBalancer loadBalancer) { 050 this.correlationExpression = correlationExpression; 051 this.loadBalancer = loadBalancer; 052 } 053 054 public void setCorrelationExpression(Expression<Exchange> 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 }