读取RDF不起作用
[英]Reading RDF does not work
问题描述
I am trying to road a foaf file: 
我正在尝试传送foaf文件：
import org.apache.jena.rdf.model.Model;
import org.apache.jena.rdf.model.ModelFactory;
public class Testbed {
public static void main(String[] args) {
Model model = ModelFactory.createDefaultModel();
try {
model.read("http://www.csail.mit.edu/~lkagal/foaf", "RDF/XML");
}
catch(Exception ex) {
System.out.println(ex.toString());
}
}
}
I am getting the following exception: 我收到以下异常：
org.apache.jena.riot.RiotException: [line: 1, col: 50] White spaces are required between publicId and systemId.
I do not understand what this exception means. 我不明白这个例外的含义。 How can I fix it. 我该如何解决。 Am I using the wrong format (does not look like "TURTLE" or any other format)? 我使用了错误的格式（看起来不像“ TURTLE”或任何其他格式）吗？
My environment (Windows 10 x64, apache-jena-3.1.1): 我的环境（Windows 10 x64，apache-jena-3.1.1）：
java version "1.8.0_112" Java(TM) SE Runtime Environment (build 1.8.0_112-b15) Java HotSpot(TM) 64-Bit Server VM (build 25.112-b15, mixed mode
1 个解决方案
解决方案1
4 已采纳 2016-12-24 01:44:48
The URL http://www.csail.mit.edu/~lkagal/foaf is actually redirecting to http://people.csail.mit.edu/lkagal/foaf . URL http://www.csail.mit.edu/~lkagal/foaf实际上是重定向到http://people.csail.mit.edu/lkagal/foaf 。 The presence of a redirect is the cause of the error. 重定向的存在是导致错误的原因。
The problem was already reported and fixed in the development branch of Jena (bug [JENA-1263] ). 该问题已经在Jena的开发分支中报告并解决（错误[JENA-1263] ）。
Analysis 分析
Apache Jena uses Apache HttpClient for connection handling. Apache Jena使用Apache HttpClient进行连接处理。 In particular, Jena 3.1.0 uses HttpClient 4.2.6 which was updated to HttpClient 4.5.2 in Jena 3.1.1 . 特别是， Jena 3.1.0使用HttpClient 4.2.6 ，该版本已在Jena 3.1.1更新为HttpClient 4.5.2 。
As @potame pointed out, the issue is not present using Jena 3.1.0 , the reason is that it creates a connection which by default supports various features, including automatically following redirects (it uses new SystemDefaultHttpClient() ). 正如@potame指出的那样，使用Jena 3.1.0不会出现此问题，原因是它创建了一个默认支持各种功能的连接，包括自动跟随重定向（它使用new SystemDefaultHttpClient() ）。
On the contrary, with the update of HttpClient , in Jena 3.1.1 the code was modified to create a more minimal type of connection that is unable to follow redirects (it uses HttpClients.createMinimal() ). 相反，随着HttpClient的更新，在Jena 3.1.1对代码进行了修改，以创建一种无法跟踪重定向的更简单的连接类型（它使用HttpClients.createMinimal() ）。
What happens is that, instead of reaching your foaf file, it just retrieves the redirect message which is: 发生的是，它没有到达您的foaf文件，而是检索了以下重定向消息：
name="[xml]",ch=DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>301 Moved Permanently</title>
</head><body>
<h1>Moved Permanently</h1>
<p>The document has moved <a href="http://people.csail.mit.edu/lkagal/foaf">here</a>.</p>
<hr>
<address>Apache/2.2.16 (Debian) Server at www.csail.mit.edu Port 80</address>
</body></html>
and then tries to parse it with Apache Xerces which is actually the one that throws the exception (you can see that by using ex.printStackTrace() instead of System.out.println(ex.toString()) ): 然后尝试使用Apache Xerces解析它，它实际上是引发异常的代码（您可以使用ex.printStackTrace()而不是System.out.println(ex.toString())看到此异常）：
...
at org.apache.xerces.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:282)
at org.apache.xerces.impl.XMLScanner.reportFatalError(XMLScanner.java:1467)
at org.apache.xerces.impl.XMLScanner.scanExternalID(XMLScanner.java:1001)
...
Solutions 解决方案
- use the direct URL,
http://people.csail.mit.edu/lkagal/foaf使用直接网址http://people.csail.mit.edu/lkagal/foaf - use a previous version of
Jena使用早期版本的Jena - use the development branch of
Jena使用Jena的发展分支 provide
Jenawith your own "redirect capable" connection, to be used instead of the default one;为Jena提供您自己的“具有重定向功能”的连接，以代替默认的连接； you can do so calling the methodHttpOp.setDefaultHttpClientprior to usemodel.read, for example:你可以这样做调用方法HttpOp.setDefaultHttpClient在使用前model.read，例如：HttpOp.setDefaultHttpClient(HttpClientBuilder.create().build());
声明:本站的技术帖子网页，遵循CC BY-SA 4.0协议，如果您需要转载，请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.