ActiveMQ example source code file (MessageQuery.java)

This example ActiveMQ source code file (MessageQuery.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - ActiveMQ tags/keywords

exception, exception, messagelistener, messagelistener, messagequery, messagequery

The ActiveMQ MessageQuery.java source code

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.activemq.broker.region.policy;

import javax.jms.MessageListener;

import org.apache.activemq.command.ActiveMQDestination;
import org.apache.activemq.command.Message;

/**
 * Represents some kind of query which will load initial messages from some source for a new topic subscriber.
 * 
 * 
 */
public interface MessageQuery {
    
    /**
     * Executes the query for messages; each message is passed into the listener
     * 
     * @param destination the destination on which the query is to be performed
     * @param listener is the listener to notify as each message is created or loaded
     */
    void execute(ActiveMQDestination destination, MessageListener listener) throws Exception;

    /**
     * Returns true if the given update is valid and does not overlap with the initial message query.
     * When performing an initial load from some source, there is a chance that an update may occur which is logically before
     * the message sent on the initial load - so this method provides a hook where the query instance can keep track of the version IDs
     * of the messages sent so that if an older version is sent as an update it can be excluded to avoid going backwards in time.
     * 
     * e.g. if the execute() method creates version 2 of an object and then an update message is sent for version 1, this method should return false to 
     * hide the old update message.
     * 
     * @param message the update message which may have been sent before the query actually completed
     * @return true if the update message is valid otherwise false in which case the update message will be discarded.
     */
    boolean validateUpdate(Message message);

}