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.AsyncCallback;
022    import org.apache.camel.AsyncProcessor;
023    import org.apache.camel.Exchange;
024    import org.apache.camel.Processor;
025    
026    /**
027     * A base class for {@link LoadBalancer} implementations which choose a single
028     * destination for each exchange (rather like JMS Queues)
029     * 
030     * @version 
031     */
032    public abstract class QueueLoadBalancer extends LoadBalancerSupport {
033    
034        public boolean process(final Exchange exchange, final AsyncCallback callback) {
035            List<Processor> list = getProcessors();
036            if (!list.isEmpty()) {
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                    if (processor instanceof AsyncProcessor) {
042                        AsyncProcessor async = (AsyncProcessor) processor;
043                        return async.process(exchange, callback);
044                    } else {
045                        try {
046                            processor.process(exchange);
047                        } catch (Exception e) {
048                            exchange.setException(e);
049                        }
050                        callback.done(true);
051                        return true;
052                    }
053                }
054            }
055    
056            // no processors but indicate we are done
057            callback.done(true);
058            return true;
059        }
060    
061        protected abstract Processor chooseProcessor(List<Processor> processors, Exchange exchange);
062    }