001/**
002 * Copyright (c) 2011, The University of Southampton and the individual contributors.
003 * All rights reserved.
004 *
005 * Redistribution and use in source and binary forms, with or without modification,
006 * are permitted provided that the following conditions are met:
007 *
008 *   *  Redistributions of source code must retain the above copyright notice,
009 *      this list of conditions and the following disclaimer.
010 *
011 *   *  Redistributions in binary form must reproduce the above copyright notice,
012 *      this list of conditions and the following disclaimer in the documentation
013 *      and/or other materials provided with the distribution.
014 *
015 *   *  Neither the name of the University of Southampton nor the names of its
016 *      contributors may be used to endorse or promote products derived from this
017 *      software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
020 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
021 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
022 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
023 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
026 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
028 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package org.openimaj.text.nlp.namedentity;
031
032import java.util.ArrayList;
033
034import com.hp.hpl.jena.query.Query;
035import com.hp.hpl.jena.query.QueryExecution;
036import com.hp.hpl.jena.query.QueryExecutionFactory;
037import com.hp.hpl.jena.query.QueryFactory;
038import com.hp.hpl.jena.query.QuerySolution;
039import com.hp.hpl.jena.query.ResultSet;
040
041/**
042 * A class to handle the page iteration through a set of results from a sparql endpoint query.
043 * Will increase the page size until failure, then resume on last successful page size.
044 * 
045 * @author Laurence Willmore (lgw1e10@ecs.soton.ac.uk)
046 * @author Sina Samangooei (ss@ecs.soton.ac.uk)
047 */
048public class SparqlQueryPager {
049        private String endPoint;
050        private int increaseFactor = 5;
051        
052        /**
053         * @param endPoint = URL string of endpoint
054         */
055        public SparqlQueryPager(String endPoint){
056                this.endPoint=endPoint;
057        }
058        
059        /**
060         * Process a query in the form of a string.
061         * @param queryString = SELECT with no LIMIT or OFFSET clauses.
062         * @return List of com.hp.hpl.jena.query.QuerySolution.
063         */
064        public ArrayList<QuerySolution> pageQuery(String queryString){
065                int rollBacks=0;
066                ArrayList<QuerySolution> result = new ArrayList<QuerySolution>();
067                int currentOffset = 0;
068                int currentChunkSize = 500;             
069                while(true){
070                        String pageQueryString = queryString+" OFFSET "+currentOffset+" LIMIT "+currentChunkSize;
071                        ArrayList<QuerySolution> subResult = fetch(pageQueryString);
072                        if(subResult==null){
073                                if(rollBacks>2)return result;
074                                currentChunkSize=currentChunkSize/increaseFactor;
075                                rollBacks++;
076                                continue;
077                        }
078                        else if(subResult.size()<currentChunkSize){
079                                result.addAll(subResult);
080                                break;
081                        }
082                        else{
083                                result.addAll(subResult);
084                                currentOffset+=currentChunkSize;
085                                currentChunkSize*=increaseFactor;
086                        }
087                }
088                return result;
089        }
090
091        private ArrayList<QuerySolution> fetch(String pageQueryString) {
092                ArrayList<QuerySolution> result = new ArrayList<QuerySolution>();
093                Query q = QueryFactory.create(pageQueryString);
094                QueryExecution qexec =QueryExecutionFactory.sparqlService(endPoint, q);
095                ResultSet results;
096                try {
097                        results = qexec.execSelect();           
098                        for (; results.hasNext();) {
099                                QuerySolution soln = results.nextSolution();
100                                result.add(soln);                               
101                        }
102                }
103                catch(Exception e){
104                        e.printStackTrace();
105                        return null;
106                }               
107                finally {
108                        qexec.close();
109                }               
110                return result;
111        }
112
113}