001 /** 002 * 003 * Licensed to the Apache Software Foundation (ASF) under one or more 004 * contributor license agreements. See the NOTICE file distributed with 005 * this work for additional information regarding copyright ownership. 006 * The ASF licenses this file to You under the Apache License, Version 2.0 007 * (the "License"); you may not use this file except in compliance with 008 * the License. You may obtain a copy of the License at 009 * 010 * http://www.apache.org/licenses/LICENSE-2.0 011 * 012 * Unless required by applicable law or agreed to in writing, software 013 * distributed under the License is distributed on an "AS IS" BASIS, 014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 015 * See the License for the specific language governing permissions and 016 * limitations under the License. 017 */ 018 package org.apache.camel.processor.loadbalancer; 019 020 import org.apache.camel.Exchange; 021 import org.apache.camel.Expression; 022 import org.apache.camel.Processor; 023 024 import java.util.HashMap; 025 import java.util.List; 026 import java.util.Map; 027 import java.util.Set; 028 import java.util.Iterator; 029 030 /** 031 * Implements a sticky load balancer using an {@link Expression} to calculate 032 * a correlation key to perform the sticky load balancing; rather like jsessionid in the web 033 * or JMSXGroupID in JMS. 034 * 035 * @version $Revision: 1.1 $ 036 */ 037 public class StickyLoadBalancer extends QueueLoadBalancer { 038 private Expression<Exchange> correlationExpression; 039 private QueueLoadBalancer loadBalancer; 040 private int numberOfHashGroups = 64 * 1024; 041 private Map<Object, Processor> stickyMap = new HashMap<Object, Processor>(); 042 043 public StickyLoadBalancer(Expression<Exchange> correlationExpression) { 044 this(correlationExpression, new RoundRobinLoadBalancer()); 045 } 046 047 public StickyLoadBalancer(Expression<Exchange> correlationExpression, QueueLoadBalancer loadBalancer) { 048 this.correlationExpression = correlationExpression; 049 this.loadBalancer = loadBalancer; 050 } 051 052 protected synchronized Processor chooseProcessor(List<Processor> processors, Exchange exchange) { 053 Object value = correlationExpression.evaluate(exchange); 054 Object key = getStickyKey(value); 055 056 Processor processor; 057 synchronized (stickyMap) { 058 processor = stickyMap.get(key); 059 if (processor == null) { 060 processor = loadBalancer.chooseProcessor(processors, exchange); 061 stickyMap.put(key, processor); 062 } 063 } 064 return processor; 065 } 066 067 @Override 068 public void removeProcessor(Processor processor) { 069 synchronized (stickyMap) { 070 Iterator<Map.Entry<Object,Processor>> iter = stickyMap.entrySet().iterator(); 071 while (iter.hasNext()) { 072 Map.Entry<Object, Processor> entry = iter.next(); 073 if (processor.equals(entry.getValue())) { 074 iter.remove(); 075 } 076 } 077 } 078 super.removeProcessor(processor); 079 } 080 081 082 // Properties 083 //------------------------------------------------------------------------- 084 public int getNumberOfHashGroups() { 085 return numberOfHashGroups; 086 } 087 088 public void setNumberOfHashGroups(int numberOfHashGroups) { 089 this.numberOfHashGroups = numberOfHashGroups; 090 } 091 092 // Implementation methods 093 //------------------------------------------------------------------------- 094 095 /** 096 * A strategy to create the key for the sticky load balancing map. 097 * The default implementation uses the hash code of the value 098 * then modulos by the numberOfHashGroups to avoid the sticky map getting too big 099 * 100 * @param value the correlation value 101 * @return the key to be used in the sticky map 102 */ 103 protected Object getStickyKey(Object value) { 104 int hashCode = 37; 105 if (value != null) { 106 hashCode = value.hashCode(); 107 } 108 if (numberOfHashGroups > 0) { 109 hashCode = hashCode % numberOfHashGroups; 110 } 111 return hashCode; 112 } 113 }