Source Code Cross Referenced for TaskExecutor.java in  » Portal » mypersonalizer » es » udc » mypersonalizer » kernel » model » tasks » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Portal » mypersonalizer » es.udc.mypersonalizer.kernel.model.tasks 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * $Header: /export/home/cvsroot/MyPersonalizerRepository/MyPersonalizer/Subsystems/Kernel/Sources/es/udc/mypersonalizer/kernel/model/tasks/TaskExecutor.java,v 1.1.1.1 2004/03/25 12:08:37 fbellas Exp $
003:         * $Revision: 1.1.1.1 $
004:         * $Date: 2004/03/25 12:08:37 $
005:         *
006:         * =============================================================================
007:         *
008:         * Copyright (c) 2003, The MyPersonalizer Development Group
009:         * (http://www.tic.udc.es/~fbellas/mypersonalizer/index.html) at 
010:         * University Of A Coruņa
011:         * All rights reserved.
012:         *
013:         * Redistribution and use in source and binary forms, with or without
014:         * modification, are permitted provided that the following conditions are met:
015:         *
016:         *  - Redistributions of source code must retain the above copyright notice, 
017:         *    this list of conditions and the following disclaimer.
018:         *
019:         *  - Redistributions in binary form must reproduce the above copyright notice,
020:         *    this list of conditions and the following disclaimer in the documentation
021:         *    and/or other materials provided with the distribution.
022:         *
023:         *  - Neither the name of the University Of A Coruņa nor the names of its 
024:         *    contributors may be used to endorse or promote products derived from 
025:         *    this software without specific prior written permission.
026:         *
027:         * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
028:         * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
029:         * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
030:         * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
031:         * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
032:         * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
033:         * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
034:         * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
035:         * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
036:         * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
037:         * POSSIBILITY OF SUCH DAMAGE.
038:         *
039:         */
040:        package es.udc.mypersonalizer.kernel.model.tasks;
041:
042:        import java.util.ArrayList;
043:        import java.util.List;
044:
045:        import es.udc.mypersonalizer.kernel.model.query.ast.Query;
046:        import es.udc.mypersonalizer.kernel.model.query.ast.Step;
047:        import es.udc.mypersonalizer.kernel.model.query.executor.QueryExecutor;
048:        import es.udc.mypersonalizer.kernel.util.exceptions.IllegalResultMetaPropertyExeception;
049:        import es.udc.mypersonalizer.kernel.util.exceptions.InternalErrorException;
050:
051:        /**
052:         * Utility class for executing a <code>Task</code> on the results of a 
053:         * <code>Query</code>.
054:         * <p>
055:         * This class takes care of retrieving the results in chunks (<em>pages</em>)
056:         * to reduce memory consumption. These <em>pages</em> are then passed to
057:         * the task. 
058:         * 
059:         * @author Abel Muinho
060:         * @since 1.0
061:         */
062:        public class TaskExecutor {
063:            /** Size of each page. */
064:            /* TODO: Should be configurable per task. */
065:            private final static int PAGE_SIZE = 500;
066:
067:            /**
068:             * Executes a <code>Task</code> on the results of a <code>Query</code>.
069:             * <p>
070:             * The results are obtained by using the <em>page-by-page iterator</em>
071:             * pattern, and the task is executed on each page of properties returned.
072:             *  
073:             * @param query the query to perform.
074:             * @param task the task to execute.
075:             * @throws InternalErrorException if the task finds errors while executing
076:             *      or errors are found performing the query.
077:             * @throws IllegalResultMetaPropertyExeception if the query is not suitable
078:             *      for the given task.
079:             */
080:            public static List execute(Query query, Task task)
081:                    throws InternalErrorException,
082:                    IllegalResultMetaPropertyExeception {
083:
084:                if (isValidQuery(query, task)) {
085:                    /* Everyting is fine. */
086:                    int start = 0;
087:                    List messages = new ArrayList();
088:                    List pageResult;
089:                    do {
090:                        pageResult = QueryExecutor.executeQuery(query, start,
091:                                PAGE_SIZE);
092:                        /* It might be an empty list, but is not often the case. */
093:                        task.execute(pageResult);
094:                        messages.addAll(task.getMessages());
095:                        start += PAGE_SIZE;
096:                    } while (pageResult.size() == PAGE_SIZE);
097:                    return messages;
098:                } else {
099:                    /* Invalid query. */
100:                    throw new IllegalResultMetaPropertyExeception();
101:                }
102:            }
103:
104:            /**
105:             * Checks if a task is compatible with the results of the query.
106:             * @param query the query.
107:             * @param task the task.
108:             * @return <code>true</code> if the task is compatible with the results
109:             *      of the query, <code>false</code> otherwise.
110:             */
111:            private static boolean isValidQuery(Query query, Task task) {
112:                /* Find target property */
113:                Step lastStep = (Step) query.getReturnClause().get(
114:                        query.getReturnClause().size() - 1);
115:
116:                return task.isCompatibleWith(lastStep.getMetaProperty());
117:            }
118:        }
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