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 */
017package org.apache.camel.processor.loadbalancer;
018
019import java.util.List;
020
021import org.apache.camel.AsyncCallback;
022import org.apache.camel.AsyncProcessor;
023import org.apache.camel.Exchange;
024import 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 */
032public 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}