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.Processor;
022    
023    import java.util.List;
024    
025    /**
026     * A base class for {@link LoadBalancer} implementations which choose a single destination for each exchange
027     * (rather like JMS Queues)
028     *
029     * @version $Revision: 1.1 $
030     */
031    public abstract class QueueLoadBalancer extends LoadBalancerSupport {
032    
033        public void process(Exchange exchange) throws Exception {
034            List<Processor> list = getProcessors();
035            if (list.isEmpty()) {
036                throw new IllegalStateException("No processors available to process " + exchange);
037            }
038            Processor processor = chooseProcessor(list, exchange);
039            if (processor == null) {
040                throw new IllegalStateException("No processors could be chosen to process " + exchange);
041            }
042            else {
043                processor.process(exchange);
044            }
045        }
046    
047        protected abstract Processor chooseProcessor(List<Processor> processors, Exchange exchange);
048    }