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.List;
020
021 import org.apache.camel.Exchange;
022 import org.apache.camel.Processor;
023 import org.apache.camel.util.ObjectHelper;
024
025 /**
026 * This FailOverLoadBalancer will failover to use next processor when an exception occured
027 */
028 public class FailOverLoadBalancer extends LoadBalancerSupport {
029
030 private final List<Class<?>> exceptions;
031
032 public FailOverLoadBalancer() {
033 this.exceptions = null;
034 }
035
036 public FailOverLoadBalancer(List<Class<?>> exceptions) {
037 this.exceptions = exceptions;
038 for (Class<?> type : exceptions) {
039 if (!ObjectHelper.isAssignableFrom(Throwable.class, type)) {
040 throw new IllegalArgumentException("Class is not an instance of Throwable: " + type);
041 }
042 }
043 }
044
045 public List<Class<?>> getExceptions() {
046 return exceptions;
047 }
048
049 /**
050 * Should the given failed Exchange failover?
051 *
052 * @param exchange the exchange that failed
053 * @return <tt>true</tt> to failover
054 */
055 protected boolean shouldFailOver(Exchange exchange) {
056 if (exchange.getException() != null) {
057
058 if (exceptions == null || exceptions.isEmpty()) {
059 // always failover if no exceptions defined
060 return true;
061 }
062
063 for (Class<?> exception : exceptions) {
064 // will look in exception hierarchy
065 if (exchange.getException(exception) != null) {
066 return true;
067 }
068 }
069 }
070
071 return false;
072 }
073
074 public void process(Exchange exchange) throws Exception {
075 List<Processor> list = getProcessors();
076 if (list.isEmpty()) {
077 throw new IllegalStateException("No processors available to process " + exchange);
078 }
079
080 int index = 0;
081 Processor processor = list.get(index);
082
083 // process the first time
084 processExchange(processor, exchange);
085
086 // loop while we should fail over
087 while (shouldFailOver(exchange)) {
088 index++;
089 if (index < list.size()) {
090 // try again but prepare exchange before we failover
091 prepareExchangeForFailover(exchange);
092 processor = list.get(index);
093 processExchange(processor, exchange);
094 } else {
095 // no more processors to try
096 break;
097 }
098 }
099 }
100
101 /**
102 * Prepares the exchange for failover
103 *
104 * @param exchange the exchange
105 */
106 protected void prepareExchangeForFailover(Exchange exchange) {
107 exchange.setException(null);
108
109 exchange.setProperty(Exchange.ERRORHANDLER_HANDLED, null);
110 exchange.setProperty(Exchange.FAILURE_HANDLED, null);
111 exchange.setProperty(Exchange.EXCEPTION_CAUGHT, null);
112 exchange.getIn().removeHeader(Exchange.REDELIVERED);
113 exchange.getIn().removeHeader(Exchange.REDELIVERY_COUNTER);
114 }
115
116 private void processExchange(Processor processor, Exchange exchange) {
117 if (processor == null) {
118 throw new IllegalStateException("No processors could be chosen to process " + exchange);
119 }
120 try {
121 processor.process(exchange);
122 } catch (Exception e) {
123 exchange.setException(e);
124 }
125 }
126
127 public String toString() {
128 return "FailoverLoadBalancer";
129 }
130
131 }