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    
024    /**
025     * A base class for {@link LoadBalancer} implementations which choose a single
026     * destination for each exchange (rather like JMS Queues)
027     * 
028     * @version $Revision: 3413 $
029     */
030    public abstract class QueueLoadBalancer extends LoadBalancerSupport {
031    
032        public void process(Exchange exchange) throws Exception {
033            List<Processor> list = getProcessors();
034            if (list.isEmpty()) {
035                throw new IllegalStateException("No processors available to process " + exchange);
036            }
037            Processor processor = chooseProcessor(list, exchange);
038            if (processor == null) {
039                throw new IllegalStateException("No processors could be chosen to process " + exchange);
040            } else {
041                processor.process(exchange);
042            }
043        }
044    
045        protected abstract Processor chooseProcessor(List<Processor> processors, Exchange exchange);
046    }