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;
018    
019    /**
020     * Represents a <a
021     * href="http://activemq.apache.org/camel/polling-consumer.html">Polling
022     * Consumer</a> where the caller polls for messages when it is ready.
023     * 
024     * @version $Revision: 706523 $
025     */
026    public interface PollingConsumer<E extends Exchange> extends Consumer<E> {
027    
028        /**
029         * Waits until a message is available and then returns it. Warning that this
030         * method could block indefinitely if no messages are available.
031         * <p/>
032         * Will return <tt>null</tt> if the consumer is not started
033         * 
034         * @return the message exchange received.
035         */
036        E receive();
037    
038        /**
039         * Attempts to receive a message exchange immediately without waiting and
040         * returning <tt>null</tt> if a message exchange is not available yet.
041         * 
042         * @return the message exchange if one is immediately available otherwise
043         *         <tt>null</tt>
044         */
045        E receiveNoWait();
046    
047        /**
048         * Attempts to receive a message exchange, waiting up to the given timeout
049         * to expire if a message is not yet available
050         * 
051         * @param timeout the amount of time in milliseconds to wait for a message
052         *                before timing out and returning <tt>null</tt>
053         * 
054         * @return the message exchange if one iwas available within the timeout
055         *         period, or <tt>null</tt> if the timeout expired
056         */
057        E receive(long timeout);
058    
059    }