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 }