| /* |
| * 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 arq.examples.bgpmatching; |
| |
| import org.apache.jena.query.* ; |
| import org.apache.jena.rdf.model.Model ; |
| import org.apache.jena.rdf.model.ModelFactory ; |
| import org.apache.jena.rdf.model.Property ; |
| import org.apache.jena.rdf.model.Resource ; |
| import org.apache.jena.sparql.engine.main.StageGenerator ; |
| import org.apache.jena.sparql.util.QueryExecUtils ; |
| |
| /** Example to execute a query but handle the |
| * basic graph patterns in the query in some special way. |
| * Stages are one step in executing a basic graph pattern (BGP). |
| * A StageGenerator builds a StageList and the stage list |
| * is executes with the output (a QueryIterator) of the previous |
| * stage fed int the current stage. |
| */ |
| |
| public class StageAltMain |
| { |
| static String NS = "http://example/" ; |
| |
| public static void main(String[] argv) |
| { |
| String[] queryString = |
| { |
| "PREFIX ns: <"+NS+">" , |
| "SELECT ?v ", |
| "{ ?s ns:p1 'xyz' ;", |
| " ns:p2 ?v }" |
| } ; |
| |
| // The stage generator to be used for a query execution |
| // is read from the context. There is a global context, which |
| // is cloned when a query execution object (query engine) is |
| // created. |
| |
| // Normally, StageGenerators are chained - a new one inspects the |
| // execution request and sees if it handles it. If it does not, |
| // it sends the request to the stage generator that was already registered. |
| |
| // The normal stage generator is registerd in the global context. |
| // This can be replaced, so that every query execution uses the |
| // alternative stage generator, or the cloned context can be |
| // alter so that just one query execution is affected. |
| |
| // Change the stage generator for all queries ... |
| if ( false ) |
| { |
| StageGenerator origStageGen = (StageGenerator)ARQ.getContext().get(ARQ.stageGenerator) ; |
| StageGenerator stageGenAlt = new StageGeneratorAlt(origStageGen) ; |
| ARQ.getContext().set(ARQ.stageGenerator, stageGenAlt) ; |
| } |
| |
| Query query = QueryFactory.create( String.join("\n", queryString)) ; |
| QueryExecution engine = QueryExecutionFactory.create(query, makeData()) ; |
| |
| // ... or set on a per-execution basis. |
| if ( true ) |
| { |
| StageGenerator origStageGen = (StageGenerator)engine.getContext().get(ARQ.stageGenerator) ; |
| StageGenerator stageGenAlt = new StageGeneratorAlt(origStageGen) ; |
| engine.getContext().set(ARQ.stageGenerator, stageGenAlt) ; |
| } |
| |
| QueryExecUtils.executeQuery(query, engine) ; |
| } |
| |
| private static Model makeData() |
| { |
| Model model = ModelFactory.createDefaultModel() ; |
| Resource r = model.createResource(NS+"r") ; |
| Property p1 = model.createProperty(NS+"p1") ; |
| Property p2 = model.createProperty(NS+"p2") ; |
| model.add(r, p1, "xyz") ; |
| model.add(r, p2, "abc") ; |
| return model ; |
| } |
| } |