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* Licensed to the Apache Software Foundation (ASF) under one
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* 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.atlas.lib.StrUtils ;
import com.hp.hpl.jena.query.ARQ ;
import com.hp.hpl.jena.query.Query ;
import com.hp.hpl.jena.query.QueryExecution ;
import com.hp.hpl.jena.query.QueryExecutionFactory ;
import com.hp.hpl.jena.query.QueryFactory ;
import com.hp.hpl.jena.rdf.model.Model ;
import com.hp.hpl.jena.rdf.model.ModelFactory ;
import com.hp.hpl.jena.rdf.model.Property ;
import com.hp.hpl.jena.rdf.model.Resource ;
import com.hp.hpl.jena.sparql.engine.main.StageGenerator ;
import com.hp.hpl.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( StrUtils.strjoin("\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 ;
}
}