# Java DOM解析器 - 解析XML文档 - Java XML教程
## 使用DOM的步骤
以下是在使用DOM解析器解析文档使用的步骤。
* 导入XML相关的软件包。
* 创建DocumentBuilder
* 从文件或流创建一个文档
* 提取根元素
* 检查属性
* 检查子元素
导入XML相关的软件包
```
import org.w3c.dom.*;
import javax.xml.parsers.*;
import java.io.*;
```
**创建 DocumentBuilder**
```
DocumentBuilderFactory factory =
DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
```
**从文件或流创建一个文档**
```
StringBuilder xmlStringBuilder = new StringBuilder();
xmlStringBuilder.append(" ");
ByteArrayInputStream input = new ByteArrayInputStream(
xmlStringBuilder.toString().getBytes("UTF-8"));
Document doc = builder.parse(input);
```
**提取根元素**
```
Element root = document.getDocumentElement();
```
**检查属性**
```
//returns specific attribute
getAttribute("attributeName");
//returns a Map (table) of names/values
getAttributes();
```
**检查子元素**
```
//returns a list of subelements of specified name
getElementsByTagName("subelementName");
//returns a list of all child nodes
getChildNodes();
```
## 演示示例
这是输入需要解析的 xml 文件：
```
dinkar
kad
dinkar
85
Vaneet
Gupta
vinni
95
jasvir
singn
jazz
90
```
**演示示例：**
_DomParserDemo.java_
```
package com.yiibai.xml;
import java.io.File;
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;
public class DomParserDemo {
public static void main(String[] args){
try {
File inputFile = new File("input.txt");
DocumentBuilderFactory dbFactory
= DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
Document doc = dBuilder.parse(inputFile);
doc.getDocumentElement().normalize();
System.out.println("Root element :"
+ doc.getDocumentElement().getNodeName());
NodeList nList = doc.getElementsByTagName("student");
System.out.println("----------------------------");
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("Student roll no : "
+ eElement.getAttribute("rollno"));
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("Marks : "
+ eElement
.getElementsByTagName("marks")
.item(0)
.getTextContent());
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
```
这将产生以下结果：
```
Root element :class
----------------------------
Current Element :student
Student roll no : 393
First Name : dinkar
Last Name : kad
Nick Name : dinkar
Marks : 85
Current Element :student
Student roll no : 493
First Name : Vaneet
Last Name : Gupta
Nick Name : vinni
Marks : 95
Current Element :student
Student roll no : 593
First Name : jasvir
Last Name : singn
Nick Name : jazz
Marks : 90
```