Apache Jena 4.9.0执行SPARQL SELECT查询遇Content-Type报错求助

使用Apache Jena 4.9.0开发工具，向Virtuoso开源版7.2.13和GraphDB 10.8.0的SPARQL端点发送SELECT查询时，触发错误：

Endpoint returned Content-Type: application/sparql-results+json which is not recognized for SELECT queries.

代码实现 #

HttpClient httpClient = HttpClient.newBuilder()
                    .connectTimeout(Duration.ofSeconds(shortTimeOut))
                    .followRedirects(Redirect.NORMAL)
                    .build();
QueryExecution gqexec = QueryExecutionHTTPBuilder
                    .service(ep)
                    .httpClient(httpClient)
                    .query(q)
                    .sendMode(QuerySendMode.asPost)
                    .timeout(longTimeOut, TimeUnit.SECONDS)
                    .build();
ResultSet rs = gqexec.execSelect();

查询语句 #

SELECT DISTINCT ?g WHERE { GRAPH ?g {?s ?p ?o} }

请求详情 #

Received POST request: POST /sparql HTTP/1.1

Headers:
Connection: Upgrade, HTTP2-Settings
Content-Length: 48
Host: localhost:8080
HTTP2-Settings: AAEAAEAAAAIAAAAAAAMAAAAAAAQBAAAAAAUAAEAAAAYABgAA
Upgrade: h2c
User-Agent: Java-http-client/21.0.5
Accept: application/sparql-results+json, application/sparql-results+xml;q=0.9, text/tab-separated-values;q=0.7, text/csv;q=0.5,application/json;q=0.2,application/xml;q=0.2,*/*;q=0.1
Content-Type: application/sparql-query;charset=utf-8

Body:
SELECT DISTINCT ?g WHERE { GRAPH ?g {?s ?p ?o} }

响应数据 #

< HTTP/1.1 200 OK
< Server: Virtuoso/07.20.3240 (Linux) x86_64-ubuntu_focal-linux-gnu
< Connection: Keep-Alive
< Date: Wed, 27 Nov 2024 09:13:32 GMT
< Accept-Ranges: bytes
< Content-disposition: filename=sparql_2024-11-27_09-13-32Z.json
< Content-Type: application/sparql-results+json
< Content-Length: 12180
<
{ [12180 bytes data]

{ "head": { "link": [], "vars": ["g"] },
  "results": { "distinct": false, "ordered": true, "bindings": [
    { "g": { "type": "uri", "value": "http://www.openlinksw.com/schemas/virtrdf#" }},
    { "g": { "type": "uri", "value": "http://www.w3.org/ns/ldp#" }},
...

原因分析 #

application/sparql-results+json是SPARQL SELECT查询的标准响应Content-Type，报错核心原因包括：

• 自定义HttpClient的配置干扰了Jena默认的响应解析逻辑，导致无法正确识别标准Content-Type；
• Jena 4.9.0对带有Content-disposition头的响应可能存在解析异常；
• 项目依赖缺失jena-sparql-json模块，导致JSON结果解析器未注册。

解决方法 #

方法1：强制指定结果格式 #

在构建QueryExecution时手动指定结果格式为JSON，跳过Content-Type自动检测：

QueryExecution gqexec = QueryExecutionHTTPBuilder
                    .service(ep)
                    .httpClient(httpClient)
                    .query(q)
                    .sendMode(QuerySendMode.asPost)
                    .timeout(longTimeOut, TimeUnit.SECONDS)
                    .format(ResultsFormat.FMT_RS_JSON) // 新增此行
                    .build();

方法2：使用Jena默认HttpClient #

移除自定义HttpClient，使用Jena自带客户端避免配置冲突：

QueryExecution gqexec = QueryExecutionHTTPBuilder
                    .service(ep)
                    .query(q)
                    .sendMode(QuerySendMode.asPost)
                    .timeout(longTimeOut, TimeUnit.SECONDS)
                    .build();

方法3：补全依赖 #

确保项目依赖中包含jena-sparql-json模块（Maven示例）：

<dependency>
    <groupId>org.apache.jena</groupId>
    <artifactId>jena-sparql-json</artifactId>
    <version>4.9.0</version>
</dependency>

方法4：针对Virtuoso的额外配置 #

若仅Virtuoso端点出现问题，可在请求URL后追加format=json参数强制指定返回格式：

QueryExecution gqexec = QueryExecutionHTTPBuilder
                    .service(ep + "?format=json") // 追加参数
                    .httpClient(httpClient)
                    .query(q)
                    .sendMode(QuerySendMode.asPost)
                    .timeout(longTimeOut, TimeUnit.SECONDS)
                    .build();

内容的提问来源于stack exchange，提问作者Yasunori