DOM 解析器，将解析整个 XML 文档并且将把所有的 XML文档信息 加载到内存当中，然后再进行操作
简言之，此技术，将 XML 文件转换成 DOM 或者说是 树形结构，然后你就可以遍历结点了。
什么是节点？
在DOM中， XML文档 中的所有信息，都是节点。
例如：<salary>200000</salary> salary是节点，200000也是节点，200000是文本节点。200000不是salary的值。
看定义：http://www.w3schools.com/dom/dom_nodes.asp Text is Always Stored in Text Nodes
警告（提示）：
DOM解析技术，速度慢，消耗很多内存.
对于大文件，通常使用 SAX技术，SAX 快速，消耗内存少。
1. DOM XML Parser Example
本例子，通过“name”获得节点，以及对应的值
D:\javaCode\staff.xml
<?xml version="1.0" encoding="UTF-8"?> <company> <staff id="1001"> <firstname>xiaohan</firstname> <lastname>yi</lastname> <nickname>xiaokai</nickname> <salary>100000</salary> </staff> <staff id="2001"> <firstname>xiaowei</firstname> <lastname>lan</lastname> <nickname>xiaowei</nickname> <salary>200000</salary> </staff> </company>
package com.domdemo;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.w3c.dom.Node;
import org.w3c.dom.Element;
import java.io.File;
public class ReadXMLFile {
public static void main(String argv[]) {
try {
File fXmlFile = new File("D:/javaCode/staff.xml");
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = documentBuilderFactory.newDocumentBuilder();
Document doc = dBuilder.parse(fXmlFile);
// optional,but recommended
// read this -
// http://stackoverflow.com/questions/13786607/normalization-in-dom-parsing-with-java-how-does-it-work
doc.getDocumentElement().normalize();
System.out.println("Root element :" + doc.getDocumentElement().getNodeName());
NodeList nList = doc.getElementsByTagName("staff");
System.out.println("-------------我是分隔线-------------------------------------------");
for (int temp = 0; temp < nList.getLength(); temp++) {
Node nNode = nList.item(temp);
System.out.println("\nCurrent Element :" + nNode.getNodeName());
if (nNode.getNodeType() == Node.ELEMENT_NODE) {
Element eElement = (Element) nNode;
System.out.println("Staff id : "+ eElement.getAttribute("id"));
System.out.println("First Name : "+ eElement.getElementsByTagName("firstname").item(0).getTextContent());
System.out.println("Last Name : "+ eElement.getElementsByTagName("lastname").item(0).getTextContent());
System.out.println("Nick Name : "+ eElement.getElementsByTagName("nickname").item(0).getTextContent());
System.out.println("Salary : "+ eElement.getElementsByTagName("salary").item(0).getTextContent());
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
运行结果：
Root element :company -------------我是分隔线------------------------------------------- Current Element :staff Staff id : 1001 First Name : xiaohan Last Name : yi Nick Name : xiaokai Salary : 100000 Current Element :staff Staff id : 2001 First Name : xiaowei Last Name : lan Nick Name : xiaowei Salary : 200000
2. Looping the Node
本例子读取同样的“staff.xml“,将展现如何一个接一个的循环节点，并且打印出节点名和值，如果有属性的话，也将属性打印出。
package com.domdemo;
import java.io.File;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
public class ReadXMLFileLoopNode {
public static void main(String[] args) {
try {
File file = new File("D:/javaCode/staff.xml");
DocumentBuilder dBuilder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
Document doc = dBuilder.parse(file);
System.out.println("Root element :" + doc.getDocumentElement().getNodeName());
if (doc.hasChildNodes()) {
printNote(doc.getChildNodes());
}
} catch (Exception e) {
System.out.println(e.getMessage());
}
}
private static void printNote(NodeList nodeList) {
for (int count = 0; count < nodeList.getLength(); count++) {
Node tempNode = nodeList.item(count);
// make sure it's element node.
if (tempNode.getNodeType() == Node.ELEMENT_NODE) {
// 获取节点名，和节点值
System.out.println("\nNode Name =" + tempNode.getNodeName() + " [OPEN]");
System.out.println("Node Value =" + tempNode.getTextContent());
if (tempNode.hasAttributes()) {
// 获取属性名，和属性值
NamedNodeMap nodeMap = tempNode.getAttributes();
for (int i = 0; i < nodeMap.getLength(); i++) {
Node node = nodeMap.item(i);
System.out.println("attr name : " + node.getNodeName());
System.out.println("attr value : " + node.getNodeValue());
}
}
if (tempNode.hasChildNodes()) {
// loop again if has child nodes
printNote(tempNode.getChildNodes());
}
System.out.println("Node Name =" + tempNode.getNodeName() + " [CLOSE]");
}
}
}
}
Root element :company Node Name =company [OPEN] Node Value = xiaohan yi xiaokai 100000 xiaowei lan xiaowei 200000 Node Name =staff [OPEN] Node Value = xiaohan yi xiaokai 100000 attr name : id attr value : 1001 Node Name =firstname [OPEN] Node Value =xiaohan Node Name =firstname [CLOSE] Node Name =lastname [OPEN] Node Value =yi Node Name =lastname [CLOSE] Node Name =nickname [OPEN] Node Value =xiaokai Node Name =nickname [CLOSE] Node Name =salary [OPEN] Node Value =100000 Node Name =salary [CLOSE] Node Name =staff [CLOSE] Node Name =staff [OPEN] Node Value = xiaowei lan xiaowei 200000 attr name : id attr value : 2001 Node Name =firstname [OPEN] Node Value =xiaowei Node Name =firstname [CLOSE] Node Name =lastname [OPEN] Node Value =lan Node Name =lastname [CLOSE] Node Name =nickname [OPEN] Node Value =xiaowei Node Name =nickname [CLOSE] Node Name =salary [OPEN] Node Value =200000 Node Name =salary [CLOSE] Node Name =staff [CLOSE] Node Name =company [CLOSE]
参考文献：
http://www.mkyong.com/java/how-to-read-xml-file-in-java-dom-parser/
