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 $Revision: 64146 $
031     */
032    public abstract class QueueLoadBalancer extends LoadBalancerSupport {
033    
034        public void process(Exchange exchange) throws Exception {
035            List<Processor> list = getProcessors();
036            if (list.isEmpty()) {
037                throw new IllegalStateException("No processors available to process " + exchange);
038            }
039            Processor processor = chooseProcessor(list, exchange);
040            if (processor == null) {
041                throw new IllegalStateException("No processors could be chosen to process " + exchange);
042            } else {
043                processor.process(exchange);
044            }
045        }
046        
047        public boolean process(final Exchange exchange, final AsyncCallback callback) {
048            boolean sync = false;
049            List<Processor> list = getProcessors();
050            if (list.isEmpty()) {
051                throw new IllegalStateException("No processors available to process " + exchange);
052            }
053            Processor processor = chooseProcessor(list, exchange);
054            if (processor == null) {
055                throw new IllegalStateException("No processors could be chosen to process " + exchange);
056            } else {
057                if (processor instanceof AsyncProcessor) {
058                    AsyncProcessor asyncProcessor = (AsyncProcessor)processor;
059                    sync = asyncProcessor.process(exchange, new AsyncCallback() {
060                        public void done(boolean sync) {
061                            // Only handle the async case...
062                            if (sync) {
063                                return;
064                            } else {
065                                callback.done(sync);                        
066                            }
067                        }
068                    });                
069                } else {
070                    try {
071                        processor.process(exchange);
072                    } catch (Exception ex) {
073                        exchange.setException(ex);
074                    }
075                    callback.done(false);                
076                }            
077            }
078            return sync;
079            
080        }
081    
082        protected abstract Processor chooseProcessor(List<Processor> processors, Exchange exchange);
083    }