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    import org.apache.camel.util.AsyncProcessorConverterHelper;
026    import org.apache.camel.util.AsyncProcessorHelper;
027    
028    /**
029     * A base class for {@link LoadBalancer} implementations which choose a single
030     * destination for each exchange (rather like JMS Queues)
031     * 
032     * @version 
033     */
034    public abstract class QueueLoadBalancer extends LoadBalancerSupport {
035    
036        public boolean process(final Exchange exchange, final AsyncCallback callback) {
037            List<Processor> list = getProcessors();
038            if (!list.isEmpty()) {
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                    AsyncProcessor albp = AsyncProcessorConverterHelper.convert(processor);
044                    boolean sync = AsyncProcessorHelper.process(albp, exchange, new AsyncCallback() {
045                        public void done(boolean doneSync) {
046                            // only handle the async case
047                            if (doneSync) {
048                                return;
049                            }
050    
051                            callback.done(false);
052                        }
053                    });
054    
055                    if (!sync) {
056                        // will continue routing asynchronously
057                        return false;
058                    }
059    
060                    callback.done(true);
061                    return true;
062                }
063            }
064    
065            // no processors but indicate we are done
066            callback.done(true);
067            return true;
068        }
069    
070        public void process(Exchange exchange) throws Exception {
071            AsyncProcessorHelper.process(this, exchange);
072        }
073    
074        protected abstract Processor chooseProcessor(List<Processor> processors, Exchange exchange);
075    }