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我對從文件讀取的模型運行SPARQL查詢，並遇到未顯示結果的問題。當我嘗試打印顯示ResultSet中的每一個解決方案，我被堵在執行帶參數模型和查詢的queryExecuteFactory時出錯
QueryExecution qe = QueryExecutionFactory.create(queryString, model);
它不顯示的查詢，而是：
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這是我的代碼：
package com.monead.androjena.demo;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
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.query.QuerySolution;
import com.hp.hpl.jena.query.ResultSet;
import com.hp.hpl.jena.query.Syntax;
import com.hp.hpl.jena.rdf.model.Model;
import com.hp.hpl.jena.rdf.model.ModelFactory;
public class SparqlCodeClass {
public String queryRemoteSparqlEndpoint() {
/**
* Use the SPARQL engine and report the results
*
* @return The number of resulting rows
*/
StringBuffer results = new StringBuffer();
try{
InputStream in = new FileInputStream(new File("storage/extSdCard/foaf.rdf"));
// Create an empty in-memory model and populate it from the graph
Model model = ModelFactory.createMemModelMaker().createModel(null);
//--results.append(model);
//Model model = ModelFactory.createDefaultModel();
model.read(in,null); // null base URI, since model URIs are absolute
//results.append(model);
//--results.append(model);
// Set the query
String queryString = "PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>"+
"PREFIX foaf: <http://xmlns.com/foaf/0.1/>"+
"SELECT DISTINCT ?name"+
"WHERE {"+
"?x rdf:type foaf:Person ."+
" ?x foaf:name ?name"+
"}"+
"ORDER BY ?name";
// Set the SPARQL endpoint URI
// String sparqlEndpointUri = "http://dbpedia.org/sparql";
results.append(queryString);
// Create a Query instance
Query query = QueryFactory.create(queryString, Syntax.syntaxARQ);
results.append(query);
// Limit the number of results returned
// Setting the limit is optional - default is unlimited
query.setLimit(10);
// Set the starting record for results returned
// Setting the limit is optional - default is 1 (and it is 1-based)
query.setOffset(1);
// QueryExecution qe = QueryExecutionFactory.sparqlService(sparqlEndpointUri, query)ว
QueryExecution qe = QueryExecutionFactory.create(queryString, model);
results.append(qe);
// Execute the query and obtain results
ResultSet resultSet = qe.execSelect();
results.append(resultSet);
// Setup a place to house results for output
// Get the column names (the aliases supplied in the SELECT clause)
List<String> columnNames = resultSet.getResultVars();
// Iterate through all resulting rows
while (resultSet.hasNext()) {
// Get the next result row
QuerySolution solution = resultSet.next();
// Iterate through the columns
for (String var : columnNames) {
// Add the column label to the StringBuffer
// results.append(var + ": ");
// Add the returned row/column data to the StringBuffer
// Data value will be null if optional and not present
if (solution.get(var) == null) {
// results.append("{null}");
// Test whether the returned value is a literal value
} else if (solution.get(var).isLiteral()) {
// results.append(solution.getLiteral(var).toString());
// Otherwise the returned value is a URI
} else {
// results.append(solution.getResource(var).getURI());
}
results.append('\n');
}
results.append("-----------------\n");
}
// Important - free up resources used running the query
qe.close();
in.close();
}
catch(FileNotFoundException e){
results.append("Error from not found");
}
catch(IOException e){
results.append("Error from io");
}
// Return the results as a String
return results.toString();
}
}