Learning XML DOM -- a typical model for parsing XML documents

The book follows ： About XML Structure 、 characteristic 、 attribute

XML DOM Learning notes

If you want to parse 、 Read 、 write in XML, Then learn XML DOM

1.XML DOM What is it ？

• XML DOM All defined XML The objects and properties of the element , And how to access them ( Interface )
• XML DOM It's for getting 、 change 、 add to 、 Delete XML The standard of elements

2.XML DOM node

• Document nodes 、 Element nodes 、 Text node （ Text in element ）、 Attribute node 、 Comment node

• Be careful ： Text is stored directly in the text node , Text nodes are stored in element nodes

<book>
    <title> The romance of The Three Kingdoms </title> 
</book>

3.DOM Node tree

• XML DOM hold XML A document is treated as a tree structure . This tree structure is called Node tree ,XML Data is constructed in the form of a tree
• All nodes can be accessed through this tree . You can modify or delete their contents , You can also create new elements
• The parent node in the tree here 、 Child node 、 At the same level （ brother ） The concept of node is the same as that of tree in data structure

<bookstore>
    <book category="cooking">
        <title lang="en">Everyday Italian</title>	// First child node 
        <author>Giada De Laurentiis</author>
        <year>2005</year>
        <price>30.00</price>						// The last child node 
    </book>
</bookstore>

4.XML Parser

• working principle ： High level programming language through XML Parser , To access and operate XML file .
  1. First XML The parser will XML Load document into XML DOM In the object
  2. XML DOM Object contains access 、 operation XML Document method function
  3. Then the high-level programming language calls XML DOM To access XML Each node of

5.XML Properties and methods

• XML DOM The properties and methods of define the programming interface

• Typical properties ( The attribute here refers to the attribute of object-oriented language , instead of XML Attribute of element )
  

• Typical method
  

• XML DOM Every node in is an object , Its possession ：

  • Important attributes ：

    • nodeName： read-only 、 Of the text node nodeName yes #text、 Of the document node nodeName yes #document

    • nodeValue： Can read but write 、 Of the text node nodeValue It's the text itself 、 The attribute node is the value of the attribute

    • nodeType：

      

6.XML DOM List of nodes (Node List)

• The node list from getElementsByTagName() Methods and childNodes Property returns
• characteristic ：
  • The order of nodes in the list is the same as XML The document shall prevail 、 Index from 0 Start
  • If you delete or add elements , The list will be automatically updated

7.XML DOM Property list (js Code )

• Property list from getElementsByTagName() Methods and attributes Property returns

• And then through something like map The way of key value pair , Take the attribute value as key Retrieve the corresponding property and call the function getNameItem()

  xmlDoc=loadXMLDoc("books.xml");
  x=xmlDoc.getElementsByTagName("book")[0].attributes;
  document.write(x.getNamedItem("category").nodeValue);
  document.write("<br>" + x.length);
  

8.XML DOM Traversing the node tree (js Code )

var x, i ,xmlDoc;	
var txt = "";
var text = "<book>" + 
"<title>Everyday Italian</title>" +
"<author>Giada De Laurentiis</author>" +
"<year>2005</year>" +
"</book>";												//  Create a XML String of form 
 
parser = new DOMParser();								// Instantiate a DOM Parser 
xmlDoc = parser.parseFromString(text,"text/xml");	   // Use the parser to parse XML character string 
 
x = xmlDoc.documentElement.childNodes;	               //documentElement  Represents the root node 
for (i = 0; i < x.length ;i++) {
    
    txt += x[i].nodeName + ": " + x[i].childNodes[0].nodeValue + "<br>";// Add up 
}
document.getElementById("demo").innerHTML = txt;// Show 

9. Find other nodes through node attributes

• parentNode： Find the parent node of the current node
• childNodes： Find the child node of the current node , Return a list of nodes
• firstChild
• lastChild
• nextSibling： The next sibling of the current node
• previousSibling： The previous sibling node of the current node

10. Operate on the node (js Code )

10.1 Get node value

• nodeValue Property is used to get the Text value

  • Element node has no text value

  xmlDoc = loadXMLDoc("book.xml");
  x = xmlDoc.getElementsByTagName("title")[0];
  y = x.childNodes[0]// Text node 
  txt = y.nodeValue;
  

• getAttribute() Method returns the value

  • Attribute nodes have text values

  xmlDoc = loadXMLDoc("book.xml");
  txt = xmlDoc.getElementByTagName("title")[0].getAttribute();
  

• getAttributeNode() Method returns Attribute node

  xmlDoc = loadXMLDoc("book.xml");
  x = xmlDoc.getElementByTagName("title")[0].getAttributeNode("lang");//lang It's the property name 
  txt = x.nodeValue;
  

10.2 Modify node values

• nodeValue Attribute is used to modify the Text value

  x.nodeValue="Easy Cooking";// By direct assignment 
  

• setAttribute() Method to change the value of an existing attribute or create a new attribute

  //  change 
  x=xmlDoc.getElementsByTagName('book');// The label is book List of element nodes 
  x[0].setAttribute("category","food"); // change 
  //  establish 
   If the property does not exist , with “category” For the property name ,“food” Create a new attribute for the attribute value 
  

• nodeValue and getAttributeNode() Use together to change the value of the attribute

  x=xmlDoc.getElementsByTagName('book');
  y=x[0].getAttributeNode("category");
  y.nodeValue = "food";
  

10.3 Delete node value

• removeChild() Method to delete the specified node , The parameter is the node to be deleted

  • When a node is deleted , All its child nodes will also be deleted

  x=xmlDoc.getElementsByTagName('book')[0];	//  hold x Set as the node to delete 
  xmlDoc.documentElement.removeChild(x);		//  Delete node x
  
  x.parentNode.removeChild(x);				//  Navigate to x Parent node , And then delete x Child node ( Delete yourself )
  
  y = x.childNodes[0];
  x.removeChild(y);							//  Delete text node 
  

• nodeValue The way of attribute value substitution , Delete a text node

  xmlDoc.getElementsByTagName("title")[0].childNodes[0].nodeValue = "";
  //xmlDoc representative XML File object 
  //xmlDoc.getElementsByTagName("title") The representative label is “title” The list of elements 
  //xmlDoc.getElementsByTagName("title")[0] Represents the first element of the element list --- One label is “title” The elements of 
  //xmlDoc.getElementsByTagName("title")[0].childNodes The representative label is “title” List of child nodes of the element , Text node 
  //xmlDoc.getElementsByTagName("title")[0].childNodes[0] Represents the first element of the text node list 
  //xmlDoc.getElementsByTagName("title")[0].childNodes[0].nodeValue Represents the value of the first text node 
  

• removeAttribute(attribute_name) Delete the attribute node according to its name

  x[0].removeAttribute("category");
  

• removeAttributeNode(node) Delete all attributes of the node according to the node

10.4 Replace node values

• replaceChild() Method to replace the specified node

  xmlDoc=loadXMLDoc("books.xml"); 	//  load XML File to object xml Doc
  x = xmlDoc.documentElement;			// x Root node 
  //  Create a new book Elements 、title Elements 、node node 
  newNode = xmlDoc.createElement("book");	//  establish book Elements 
  newTitle = xmlDoc.createElement("title");//  establish title Elements 
  newText = xmlDoc.createTextNode("A Notebook");// Create text node 
  
  //  Form a parent-child relationship by adding 
  newTitle.appendChild(newText);	//  Add a text node to newTitle In the elements 
  newNode.appendChild(newTitle);	//  take title Element added to newNode in 
  
  //  Replacement node 
  y = x.getElementByTagName("book")[0]// y Is the first child node 
  x.replaceChild(newNode,y);// take x Child nodes of y Replace replace by newNode
  

• nodeValue Property substitution Text node The text in the （ Same as 10.3 Usage of ）

10.5 Create nodes

• createElement() Method to create a new element node
• createAttribute() Used to create a new attribute node , Create first, then assign
• createTextNode() Method to create a new text node
• createCDATASection() Method to create a new CDATA section node
• createComment() Method to create a new annotation node

10.6 Add a node

• appendChild() Method ： if x object Call the method , It's in x object Add a child node after the existing node

• insertBefore(node1,node2) Method ： if x object Call the method , It's in node2 Insert before the child node node1 Child node

• insertData() Method to insert data into an existing text node

  x=xmlDoc.getElementsByTagName("title")[0].childNodes[0];
  
  x.insertData(0,"Easy ");	//  stay 0 Position start , Insert "Easy " character string 
  

10.7 Clone node

• cloneNode(true/false) Method to create a copy of the specified node ;
  • true It means copying the attributes and child nodes of the cloned node

The book follows ： How to use C# Language parsing operation XML file