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: }
|