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.spi;
018    
019    import org.apache.camel.Consumer;
020    import org.apache.camel.Endpoint;
021    
022    /**
023     * Strategy for a {@link org.apache.camel.PollingConsumer} when polling an {@link org.apache.camel.Endpoint}.
024     * <p/>
025     * This pluggable strategy allows to plugin different implementations what to do, most noticeable what to
026     * do in case the polling goes wrong. This can be handled in the
027     * {@link #rollback(org.apache.camel.Consumer , org.apache.camel.Endpoint , int, Exception) rollback} method.
028     *
029     * @version 
030     */
031    public interface PollingConsumerPollStrategy {
032    
033        /**
034         * Called when poll is about to begin
035         *
036         * @param consumer the consumer
037         * @param endpoint the endpoint being consumed
038         * @return <tt>true</tt> to begin polling, or <tt>false</tt> to skip polling this time.
039         */
040        boolean begin(Consumer consumer, Endpoint endpoint);
041    
042        /**
043         * Called when poll is completed successfully
044         *
045         * @param consumer the consumer
046         * @param endpoint the endpoint being consumed
047         * @param polledMessages number of messages polled, will be <tt>0</tt> if no message was polled at all.
048         */
049        void commit(Consumer consumer, Endpoint endpoint, int polledMessages);
050    
051        /**
052         * Called when poll failed
053         *
054         * @param consumer the consumer
055         * @param endpoint the endpoint being consumed
056         * @param retryCounter current retry attempt, starting from 0.
057         * @param cause the caused exception
058         * @throws Exception can be used to rethrow the caused exception. Notice that thrown an exception will
059         *         terminate the scheduler and thus Camel will not trigger again. So if you want to let the scheduler
060         *         to continue to run then do <b>not</b> throw any exception from this method.
061         * @return whether to retry immediately or not. Return <tt>false</tt> to ignore the problem,
062         *         <tt>true</tt> to try immediately again
063         */
064        boolean rollback(Consumer consumer, Endpoint endpoint, int retryCounter, Exception cause) throws Exception;
065    
066    }