使用耶拿查询DBpedia端点时出现问题（HttpException：500 HTTP）

Question

我正在尝试使用Jena API从DBpedia端点获取给定类的所有实例。我注意到结果集限制为10000个项目。因此，对于那些具有超过10000的类，我编写了以下代码。但是，此代码引发异常（ HttpException：500 HTTP 500错误，导致查询：SPARQL请求失败）。当类的实例少于40000个时（例如City），代码可以正常运行。对于那些拥有超过40000个类的类（例如person），将抛出执行。有人可以帮我解决这个问题吗？

例外

HttpException: 500 HTTP 500 error making the query: SPARQL Request Failed
    at org.apache.jena.sparql.engine.http.HttpQuery.rewrap(HttpQuery.java:370)
    at org.apache.jena.sparql.engine.http.HttpQuery.execGet(HttpQuery.java:336)
    at org.apache.jena.sparql.engine.http.HttpQuery.exec(HttpQuery.java:288)
    at org.apache.jena.sparql.engine.http.QueryEngineHTTP.execResultSetInner(QueryEngineHTTP.java:351)
    at org.apache.jena.sparql.engine.http.QueryEngineHTTP.execSelect(QueryEngineHTTP.java:344)
    at org.jgnn.testes.dbpedia.DBpediaSPARQLDemo.getNumberOfInstancesByClassAndEndpoint(DBpediaSPARQLDemo.java:1637)
    at org.jgnn.testes.dbpedia.DBpediaSPARQLDemo.getNumberOfInstancesByClass(DBpediaSPARQLDemo.java:1602)
    at org.jgnn.testes.dbpedia.DBpediaSPARQLDemo.main(DBpediaSPARQLDemo.java:103)

public static int getNumberOfInstancesByClassAndEndpoint(String dbo_class,String regex_dbr, String sparqlEnpoint){


    int offset=0;
    int limit=10000;
    //total number of instances 
    int numberOfInstances=0;
    //number of instances of the iteration
    int numberOfInstancesOfIter=1;

    String dbo_class="dbo:Person";

    while (numberOfInstancesOfIter!=0) {
        String queryString="PREFIX dbo:<http://dbpedia.org/ontology/>\n"+
                "SELECT  DISTINCT ?x \n"+
                "WHERE \n"+
                "{ "+

                    "?x  a "+dbo_class+ " ."+ 
                 "} ORDER BY ?x LIMIT "+
                 limit+" OFFSET "+ offset;

        org.apache.jena.query.Query   query  = QueryFactory.create(queryString.toString());

        // Remote execution.
        try ( QueryExecution qexec = QueryExecutionFactory.sparqlService("http://dbpedia.org/sparql", query) ) {
            // Set the DBpedia specific timeout.
            ((QueryEngineHTTP)qexec).setTimeout(120, TimeUnit.SECONDS, 120, TimeUnit.SECONDS); 

            // Execute.
            ResultSet rs = qexec.execSelect();

            while(rs.hasNext()){               
                QuerySolution qs=rs.next();                 
            }
            //how many instances in this iteration?
            numberOfInstancesOfIter=rs.getRowNumber();

            //update instance number
            numberOfInstances+=numberOfInstancesOfIter;
            //it ends if the number of intances of iteration is less than the limit
            if(numberOfInstancesOfIter < limit ){
                numberOfInstancesOfIter=0;
            }

            if (!(numberOfInstances==0)){
                System.out.println("ok");
            }

            java.util.concurrent.TimeUnit.SECONDS.sleep(2);
        } catch (Exception e) {
            e.printStackTrace();
        }

        offset+=limit;

    }//while

    System.out.println("Number of instances of "+dbo_class +" is :"+numberOfInstances);