Java DOM解析器 - 解析XML文件

使用DOM的步驟

以下是在使用DOM解析器解析文件使用的步驟。

• 匯入XML相關的軟體包。

• 建立DocumentBuilder

• 從檔案或流建立一個文件

• 提取根元素

• 檢查屬性

• 檢查子元素

匯入XML相關的軟體包

import org.w3c.dom.*;
import javax.xml.parsers.*;
import java.io.*;

建立 DocumentBuilder

DocumentBuilderFactory factory =
DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();

從檔案或流建立一個文件

StringBuilder xmlStringBuilder = new StringBuilder();
xmlStringBuilder.append("<?xml version="1.0"?> <class> </class>");
ByteArrayInputStream input =  new ByteArrayInputStream(
   xmlStringBuilder.toString().getBytes("UTF-8"));
Document doc = builder.parse(input);

提取根元素

Element root = document.getDocumentElement();

檢查屬性

//returns specific attribute
getAttribute("attributeName"); 
//returns a Map (table) of names/values
getAttributes(); 

檢查子元素

//returns a list of subelements of specified name
getElementsByTagName("subelementName"); 
//returns a list of all child nodes
getChildNodes(); 

演示範例

這是輸入需要解析的 xml 檔案：

<?xml version="1.0"?>
<class>
   <student rollno="393">
      <firstname>dinkar</firstname>
      <lastname>kad</lastname>
      <nickname>dinkar</nickname>
      <marks>85</marks>
   </student>
   <student rollno="493">
      <firstname>Vaneet</firstname>
      <lastname>Gupta</lastname>
      <nickname>vinni</nickname>
      <marks>95</marks>
   </student>
   <student rollno="593">
      <firstname>jasvir</firstname>
      <lastname>singn</lastname>
      <nickname>jazz</nickname>
      <marks>90</marks>
   </student>
</class>

演示範例：

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();
      }
   }
}

這將產生以下結果：

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