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 }