| /** |
| * 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 tdb.examples; |
| |
| import org.apache.jena.query.*; |
| import org.apache.jena.system.Txn; |
| import org.apache.jena.tdb.TDBFactory ; |
| |
| /** |
| * Example of a READ transaction. |
| * See {@link Txn#executeRead}. |
| */ |
| public class ExTDB_Txn1 |
| { |
| public static void main(String... argv) |
| { |
| String directory = "MyDatabases/DB1"; |
| Dataset dataset = TDBFactory.createDataset(directory); |
| |
| // Start READ transaction. |
| // No updates or changes to the dataset are possible while this |
| // dataset is used for a read transaction. |
| // An application can have other Datasets, in the same JVM, |
| // tied to the same TDB database performing read or write |
| // transactions concurrently. |
| |
| // A READ transaction is |
| // dataset.begin(ReadWrite.READ); |
| // try { |
| // ... |
| // ... The app can also call dataset.abort() or dataset.commit() here; commit is not necessary |
| // } finally { dataset.end();} |
| |
| // Use Txn.executeRead when the app knows there are no updates. |
| // Can use Txn.execute when a write is possible. |
| Txn.executeRead(dataset, ()-> { |
| // Do some queries |
| String sparqlQueryString1 = "SELECT (count(*) AS ?count) { ?s ?p ?o }"; |
| execQuery(sparqlQueryString1, dataset); |
| |
| String sparqlQueryString2 = "SELECT * { ?s ?p ?o }"; |
| execQuery(sparqlQueryString2, dataset); |
| }); |
| } |
| |
| public static void execQuery(String sparqlQueryString, Dataset dataset) |
| { |
| Query query = QueryFactory.create(sparqlQueryString); |
| try ( QueryExecution qexec = QueryExecutionFactory.create(query, dataset) ) { |
| ResultSet results = qexec.execSelect(); |
| for ( ; results.hasNext() ; ) { |
| QuerySolution soln = results.nextSolution(); |
| int count = soln.getLiteral("count").getInt(); |
| System.out.println("count = " + count); |
| } |
| } |
| } |
| } |