如何通过元素ID读取XML？

Question

这是我现在的XML文件，它给了我不同字符的对话，或者至少它应该。我希望它能够工作，以便我可以指定实体标识和选项/任务标识并获取输出。所以我该怎么做？任何帮助表示赞赏，非常感谢。

<?xml version="1.0"?> 
<dialoge> 
<entity id="1"> <!-- questgiver --> 
    <quest id="1"> 
     <option id="1"> 
      <precondition>player has not started quest</precondition> 
      <output>hello there, can you kill 2 enemies for me?</output> 
     </option> 
     <option id="2"> 
      <precondition>player has completed quest and player has not...</precondition> 
      <output>thankyou, have a sword for your troubles.</output> 
     </option> 
     <option id="3"> 
      <precondition>player has not finished quest</precondition> 
      <output>you haven't finished yet.</output> 
     </option> 
     <option id="4"> 
      <outpur>thank you.</outpur> 
     </option> 
    </quest> 
</entity> 
<entity id="2"> <!-- villager --> 
    <option id="1"> 
     <precondition>village is being destroyed</precondition> 
     <output>our village is being destroyed, please help us!</output> 
    </option> 
    <option id="2"> 
     <precondition>village has been saved or destroyed</precondition> 
     <output>we will never forget this.</output> 
    </option> 
    <option id="3"> 
     <output>hello.</output> 
    </option> 
</entity> 
</dialoge> 

这是我目前有，但它不起作用。我知道这可能是一个愚蠢的问题，但我无法在网络上的任何地方找到答案。谢谢。

public static void read() { 
    try { 
     File file = new File("text.xml"); 
     DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); 
     DocumentBuilder db = dbf.newDocumentBuilder(); 
     Document doc = db.parse(file); 
     doc.getDocumentElement().normalize(); 

     System.out.println("root of xml file " + doc.getDocumentElement().getNodeName()); 
     NodeList nodes = doc.getElementsByTagName("entity"); 
     System.out.println("=========================="); 

     for(int i = 0; i < nodes.getLength(); i++) { 
      Node node = nodes.item(i); 
      if(node.getNodeType() == Node.ELEMENT_NODE) { 
       Element element = (Element) node; 
         if(element.getElementsByTagName("entity").item(0).getTextContent().equals("output")) { 

       } 
       System.out.println("" + getValue("output", element)); 
      } 
     } 
    }catch(Exception e) { 
     e.printStackTrace(); 
    } 
} 

private static String getValue(String tag, Element element) { 
    NodeList nodes = element.getElementsByTagName(tag).item(0).getChildNodes(); 
    Node node = (Node) nodes.item(0); 
    return node.getNodeValue(); 
} 

Answer 1

最简单的方法可能是使用XPath ......

try { 
    File file = new File("text.xml"); 
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); 
    DocumentBuilder db = dbf.newDocumentBuilder(); 
    Document doc = db.parse(file); 
    doc.getDocumentElement().normalize(); 

    XPath xpath = XPathFactory.newInstance().newXPath(); 
    XPathExpression xExpress = xpath.compile("//*[@id='1']"); 
    NodeList nl = (NodeList) xExpress.evaluate(doc, XPathConstants.NODESET); 
    System.out.println("Found " + nl.getLength() + " matches"); 
} catch (Exception e) { 
    e.printStackTrace(); 
} 

XPath查询//*[@id='1']会发现其中有属性id与1

有价文件中的所有节点看看WC3 XPath Tutorial和How XPath works关于XPath的更多细节

Answer 2

一般来说， DOM更容易使用，但在开始使用之前会分析entire XML，因为SAX parser正在解析XML，并且遇到标签开始（例如， <something>），则触发startElement事件（事件的实际名称可能不同）。 read more..

见Java教程上Parsing an XML File Using SAX

下面是示例代码：

import javax.xml.parsers.SAXParser; 
import javax.xml.parsers.SAXParserFactory; 

import org.xml.sax.Attributes; 
import org.xml.sax.SAXException; 
import org.xml.sax.helpers.DefaultHandler; 

public class GetElementAttributesInSAXXMLParsing extends DefaultHandler { 

    public static void main(String[] args) throws Exception { 
     DefaultHandler handler = new GetElementAttributesInSAXXMLParsing(); 
     SAXParserFactory factory = SAXParserFactory.newInstance(); 
     factory.setValidating(false); 
     SAXParser parser = factory.newSAXParser(); 
     parser.parse(new File("text.xml"), handler);  
    } 

    @Override 
    public void startElement(String uri, String localName, String qName, Attributes attributes) 
      throws SAXException { 

     System.out.println("Tag Name:"+qName); 
     // get the number of attributes in the list 
     int length = attributes.getLength(); 

     // process each attribute 
     for (int i = 0; i < length; i++) { 

      // get qualified (prefixed) name by index 
      String name = attributes.getQName(i); 
      System.out.println("Attribute Name:" + name); 

      // get attribute's value by index. 
      String value = attributes.getValue(i); 
      System.out.println("Attribute Value:" + value); 
     } 
    } 
}