Question

我们有一个叫做Virtuoso的Java应用程序。如果它在Virtuoso执行检查点时运行某些SPARQL查询，则会给出："com.hp.hpl.jena.sparql.engine.http.QueryExceptionHTTP: File not found"

我的第一个想法是因为CheckpointSyncMode=2，它会阻止查询。但是我在CheckpointSyncMode=1时设法得到了这个例外。

不幸的是，我无法复制比方法调用更多的代码;但我可以使用任何SPARQL查询重现它。

ResponseResult resultsAndBindings = APIEndpointUtil.call(req, nb, match, contextPath, queryParams);

这是stacktrace：

HttpException: 404 File not found
at com.hp.hpl.jena.sparql.engine.http.HttpQuery.execCommon(HttpQuery.java:446)
at com.hp.hpl.jena.sparql.engine.http.HttpQuery.execPost(HttpQuery.java:344)
at com.hp.hpl.jena.sparql.engine.http.HttpQuery.exec(HttpQuery.java:239)
at com.hp.hpl.jena.sparql.engine.http.QueryEngineHTTP.execSelect(QueryEngineHTTP.java:302)
at com.epimorphics.lda.sources.SourceBase.executeSelect(SourceBase.java:110)
at com.epimorphics.lda.query.APIQuery.requestTotalCount(APIQuery.java:917)
at com.epimorphics.lda.core.APIEndpointImpl.call_revised(APIEndpointImpl.java:112)
at com.epimorphics.lda.core.APIEndpointImpl.call(APIEndpointImpl.java:92)
at com.epimorphics.lda.core.APIEndpointUtil.call(APIEndpointUtil.java:53)

在非常简单的测试环境中重现：

我设置了一个空的Virtuoso实例：

OpenLink Virtuoso Server
Version 07.20.3215-pthreads for Linux as of Jan 20 2016"

CheckpointSyncMode=2或CheckpointSyncMode=1并不重要;无论如何它都会发生。

确保Virtuoso忙于检查点：

#!/bin/bash

while true; do
    isql-vt 1111 dba dba exec="checkpoint;"
done;

使用Jena（使用：com.epimorphics.lda:elda-lda:1.3.16，jena-core:2.10.1）调用端点：

import com.hp.hpl.jena.query.ParameterizedSparqlString;
import com.hp.hpl.jena.query.QueryExecution;
import com.hp.hpl.jena.query.QueryExecutionFactory;
import com.hp.hpl.jena.query.QuerySolution;

public class Main {

    public static void main(String args[]){

        while(true)
            getPreviousSnapshot();
    }

    public static void getPreviousSnapshot() {

        ParameterizedSparqlString pss = new ParameterizedSparqlString("SELECT DISTINCT ?g WHERE {  GRAPH ?g {    ?s ?p ?o  }}");

        System.out.println("Executing SPARQL query:" + pss.toString());

        QueryExecution qe = QueryExecutionFactory.sparqlService("http://33.33.33.11:8890/sparql", pss.asQuery());
        com.hp.hpl.jena.query.ResultSet resultSet = qe.execSelect();

        processResultSet(resultSet);
        qe.close();

    }

    private static void processResultSet(com.hp.hpl.jena.query.ResultSet results) {

        while (results.hasNext()) {
            QuerySolution qs = results.next();
            String s = qs.getResource("g").toString();
            System.out.println(s);

        }
    }
}

输出：

Executing SPARQL query:SELECT DISTINCT ?g WHERE {  GRAPH ?g {    ?s ?p ?o  }}
http://www.openlinksw.com/schemas/virtrdf#
http://www.w3.org/ns/ldp#
http://localhost:8890/sparql
http://localhost:8890/DAV/
http://www.w3.org/2002/07/owl#
Executing SPARQL query:SELECT DISTINCT ?g WHERE {  GRAPH ?g {    ?s ?p ?o  }}
Exception in thread "main" HttpException: 404 File not found
    at com.hp.hpl.jena.sparql.engine.http.HttpQuery.execCommon(HttpQuery.java:446)
    at com.hp.hpl.jena.sparql.engine.http.HttpQuery.execGet(HttpQuery.java:289)
    at com.hp.hpl.jena.sparql.engine.http.HttpQuery.exec(HttpQuery.java:240)
    at com.hp.hpl.jena.sparql.engine.http.QueryEngineHTTP.execSelect(QueryEngineHTTP.java:302)
    at Main.getPreviousSnapshot(Main.java:21)
    at Main.main(Main.java:11)

Answer 1

根据我在virtuoso邮件列表上得到的答案：当由于执行检查点（这是Virtuoso中的原子操作）而暂时无法访问Virtuoso时，Jena与SPARQL服务没有任何关联，因此只返回404错误

为什么在Virtuoso检查站期间我得到'404 File not found`（通过Jena）？

1 个答案: