如何構建DOM樹？

Question

<?xml version="1.0" encoding="UTF-8" ?> 
<!DOCTYPE people SYSTEM "validator.dtd"> 

<people> 
    <student> 
     <name>John</name> 
     <course>Computer Technology</course> 
     <semester>6</semester> 
     <scheme>E</scheme> 
    </student> 

    <student> 
     <name>Foo</name> 
     <course>Industrial Electronics</course> 
     <semester>6</semester> 
     <scheme>E</scheme> 
    </student> 
</people>  

這是我的XML文檔。我已經做了這個樹的表示。

這棵樹表示是正確的還是錯誤的？

Answer 1

您可以只打印DOM樹得到一個不錯的主意：

public static void main(String[] args) throws UnsupportedEncodingException, IOException, ParserConfigurationException, SAXException { 
    final String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\" ?>" 
      + "<people>" 
      + " <!-- a comment -->" 
      + " <student>" 
      + "  <name>John</name>" 
      + "  <!-- a comment -->" 
      + "  <course>Computer Technology</course>" 
      + "  <semester>6</semester>" 
      + "  <scheme>E</scheme>" 
      + " </student>" 
      + "" 
      + " <student>" 
      + "  <name>Foo</name>" 
      + "  <course>Industrial Electronics</course>" 
      + "  <semester>6</semester>" 
      + "  <scheme>E</scheme>" 
      + " </student>" 
      + "</people>"; 
    final Document document = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(new ByteArrayInputStream(xml.getBytes())); 
    printNodes(document.getDocumentElement(), 0); 
} 

private static void printNodes(final Node node, final int depth) { 
    final StringBuilder prefix = new StringBuilder(); 
    for (int i = 0; i < depth; ++i) { 
     prefix.append("\t"); 
    } 
    if (node.getNodeType() == Node.ELEMENT_NODE) { 
     System.out.println(prefix.toString() + "Going into " + node.getNodeName()); 
     final NodeList nodeList = node.getChildNodes(); 
     for (int i = 0; i < nodeList.getLength(); ++i) { 
      printNodes(nodeList.item(i), depth + 1); 
     } 
    } else if (node.getNodeType() == Node.COMMENT_NODE) { 
     System.out.println(prefix.toString() + "Comment node: \"" + node.getTextContent() + "\""); 
    } else { 
     System.out.println(prefix.toString() + "Text node: \"" + node.getTextContent() + "\""); 
    } 
} 

的這個輸出是：

Going into people 
    Text node: " " 
    Comment node: " a comment " 
    Text node: " " 
    Going into student 
     Text node: "  " 
     Going into name 
      Text node: "John" 
     Text node: "  " 
     Comment node: " a comment " 
     Text node: "  " 
     Going into course 
      Text node: "Computer Technology" 
     Text node: "  " 
     Going into semester 
      Text node: "6" 
     Text node: "  " 
     Going into scheme 
      Text node: "E" 
     Text node: " " 
    Text node: " " 
    Going into student 
     Text node: "  " 
     Going into name 
      Text node: "Foo" 
     Text node: "  " 
     Going into course 
      Text node: "Industrial Electronics" 
     Text node: "  " 
     Going into semester 
      Text node: "6" 
     Text node: "  " 
     Going into scheme 
      Text node: "E" 
     Text node: " " 

正如你可以看到有文本節點無處不在，之間可見節點。這是因爲，在理論上，有文字周圍子節點 - 例如

<student> 
    some random text 
    <course>Computer</course> 
    some more text 
</student> 

所以DOM樹需要考慮到這一點。如果XML不是非常漂亮，而只是一行，那麼下一個節點將是空的而不是空白。

翻閱文檔，看看它對輸出有什麼影響。