xpath包含Java中的名称空间的问题(Dom解析器) [英] Issues with xpath that contained namespaces in Java (Dom parser)

问题描述

我正在尝试解析rdfs xml文件，以便在rdfs文件中查找所有类.

I'm trying to parse an rdfs xml file in order to find all the Classes in an rdfs file.

xpath:"/rdf:RDF/rdfs:Class" 在我的XML编辑器中工作. 当我在Java程序中插入xpath时(我已经实现了dom解析器)，我得到0个类. 下面的示例运行，但输出0个类！

The xpath: "/rdf:RDF/rdfs:Class" is working in my XML editor. When i insert the xpath in my Java program (i have implemented a dom parser), i get 0 Classes. The following example runs but it outputs 0 classes!

我愿意

import java.io.IOException;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPathExpressionException;
import org.xml.sax.SAXException;

public class Main {
public static void main(String args[]) throws XPathExpressionException, ParserConfigurationException, SAXException, IOException{

    FindClasses FSB = new FindClasses();
    FSB.FindAllClasses("C:\\Workspace\\file.xml"); //rdfs file
     }
}

FindClasses类如下:

The class FindClasses is as follows:

import java.io.IOException;
import java.util.Collection;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

public class FindClasses {

public void FindAllClasses(String fileName) throws XPathExpressionException, ParserConfigurationException, SAXException, IOException {


    DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
    domFactory.setNamespaceAware(true); 
    DocumentBuilder builder = domFactory.newDocumentBuilder();
    Document doc = builder.parse(fileName);

    XPath xpath = XPathFactory.newInstance().newXPath();
    XPathExpression classes_expr = xpath.compile("/rdf:RDF/rdfs:Class");

    Object result = classes_expr.evaluate(doc, XPathConstants.NODESET);
    NodeList classes = (NodeList) result;

    System.out.println("I found : " + classes.getLength() + " classes " );

        }
    }

rdfs文件为:

<?xml version="1.0" encoding="UTF-8"?>
<rdf:RDF xml:lang="en" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#">
        <rdfs:Class rdf:about="Class1">
        </rdfs:Class>
        <rdfs:Class rdf:about="Class2">
        </rdfs:Class>
</rdf:RDF>  

我不太了解为什么xpath在该示例中返回0个节点. 这很奇怪，因为我也实现了其他dom解析器，并且它们工作正常. 有人可以帮我吗?

I don't really understand why the xpath returns 0 nodes in that example. It's weird, cause i have implemented other dom parsers as well and they were working fine. Can somebody help me?

谢谢

推荐答案

我访问了以下链接，并解决了我的问题: Java中的xpath问题

I visited the following link and i solved my problem: Issues with xpath in java

问题是xpath包含两个名称空间(rdf，rdfs)，例如"/rdf:RDF/rdfs:Class". 如果xpath不包含任何名称空间，例如/RDF/Class，就不会有问题了.

The problem was that the xpath contained two namespaces (rdf,rdfs) like "/rdf:RDF/rdfs:Class". If the xpath didn't contain any namespace e.g. /RDF/Class , there was not going to be an issue.

因此，在该行的之后:

xpath = XPathFactory.newInstance().newXPath();

和在该行之前:

XPathExpression classes_expr = xpath.compile("/rdf:RDF/rdfs:Class");    

我添加了以下内容:

xpath.setNamespaceContext(new NamespaceContext() {
    public String getNamespaceURI(String prefix) {
      switch (prefix) {
        case "rdf": return "http://www.w3.org/1999/02/22-rdf-syntax-ns#";
        case "rdfs" : return "http://www.w3.org/2000/01/rdf-schema#"; 
       }
    return prefix;

    }
    public String getPrefix(String namespace) {
        if (namespace.equals("rdf")) return "rdf";
        else if (namespace.equals("rdfs")) return "rdfs";
        else return null;
       }
    @Override
    public Iterator getPrefixes(String arg0) {
        // TODO Auto-generated method stub
        return null;
    }
    }); 

这篇关于xpath包含Java中的名称空间的问题(Dom解析器)的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！