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Java中解析XML的方式有哪些

时间:2022-05-19 帮助过:3人阅读 来源: php中文网

java解析XML的方式有使用DOM解析通过DOM对象以树状结构连接在一起;使用SAX 解析它是遇到不同元素时会逐行解析;使用StAX解析会从XML中提取所需的数据

XML是一种通用的数据交换格式,它的平台无关性、语言无关性、系统无关性、给数据集成与交互带来了极大的方便。接下来将要在文章中为大家具体介绍在Java中解析XML的方式,具有一定的参考作用,希望对大家有所帮助

【推荐课程:XML教程

使用DOM解析

DOM解析器主要用于在内存中使用XML作为对象图(树状结构) 也就是文档对象模型(DOM)。首先解析器遍历输入XML文件并创建与XML文件中的节点相对应的DOM对象。这些DOM对象以树状结构链接在一起。一旦解析器完成了解析过程,就会从中获得这个类似树的DOM对象结构。

例:在所有代码示例中解析xml内容

public class DOMParserDemo {
 
  public static void main(String[] args) throws Exception {
    DocumentBuilderFactory factory =
        DocumentBuilderFactory.newInstance();
    DocumentBuilder builder = factory.newDocumentBuilder();
    Document document =
      builder.parse(
        ClassLoader.getSystemResourceAsStream("xml/employee.xml"));
    List<Employee> empList = new ArrayList<>();
    NodeList nodeList = document.getDocumentElement().getChildNodes();
    for (int i = 0; i < nodeList.getLength(); i++) {
      Node node = nodeList.item(i);
      if (node instanceof Element) {
        Employee emp = new Employee();
        emp.id = node.getAttributes().
            getNamedItem("id").getNodeValue();
        NodeList childNodes = node.getChildNodes();
        for (int j = 0; j < childNodes.getLength(); j++) {
          Node cNode = childNodes.item(j);
          if (cNode instanceof Element) {
            String content = cNode.getLastChild().
                getTextContent().trim();
            switch (cNode.getNodeName()) {
              case "firstName":
                emp.firstName = content;
                break;
              case "lastName":
                emp.lastName = content;
                break;
              case "location":
                emp.location = content;
                break;
            }
          }
        }
        empList.add(emp);
      }
    }
   
    for (Employee emp : empList) {
      System.out.println(emp);
    }
 
  }
}
class Employee{
  String id;
  String firstName;
  String lastName;
  String location;
 
  @Override
  public String toString() {
    return firstName+" "+lastName+"("+id+")"+location;
  }
}

输出结果为:

Rakesh Mishra(111)Bangalore
John Davis(112)Chennai
Rajesh Sharma(113)Pune

使用SAX 解析

SAX Parser与DOM解析器的不同之处在于SAX解析器不会将完整的XML加载到内存中,而是在遇到不同的元素时,它逐行解析XML,c触发不同的事件,例如:打开标记,结束标记,字符数据,评论等。

使用SAX Parser解析XML的代码如下:

import java.util.ArrayList;
import java.util.List;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
public class SAXParserDemo {
  public static void main(String[] args) throws Exception {
    SAXParserFactory parserFactor = SAXParserFactory.newInstance();
    SAXParser parser = parserFactor.newSAXParser();
    SAXHandler handler = new SAXHandler();
    parser.parse(ClassLoader.getSystemResourceAsStream("xml/employee.xml"),
                 handler);
    for ( Employee emp : handler.empList){
      System.out.println(emp);
    }
  }
}
class SAXHandler extends DefaultHandler {
 
  List<Employee> empList = new ArrayList<>();
  Employee emp = null;
  String content = null;
  @Override
  public void startElement(String uri, String localName,
                           String qName, Attributes attributes)
                           throws SAXException {
       
    switch(qName){
      case "employee":
        emp = new Employee();
        emp.id = attributes.getValue("id");
        break;
    }
  }
 
  @Override
  public void endElement(String uri, String localName,
                         String qName) throws SAXException {
   switch(qName){
     case "employee":
       empList.add(emp);      
       break;
     case "firstName":
       emp.firstName = content;
       break;
     case "lastName":
       emp.lastName = content;
       break;
     case "location":
       emp.location = content;
       break;
   }
  }
 
  @Override
  public void characters(char[] ch, int start, int length)
          throws SAXException {
    content = String.copyValueOf(ch, start, length).trim();
  }
     
}
 
class Employee {
  String id;
  String firstName;
  String lastName;
  String location;
 
  @Override
  public String toString() {
    return firstName + " " + lastName + "(" + id + ")" + location;
  }
}

输出结果为:

Rakesh Mishra(111)Bangalore
John Davis(112)Chennai
Rajesh Sharma(113)Pune

使用StAX Parser

StAX用于XML的Streaming API,而StAX Parser与SA的不同之处在于SAX Parser。StAX解析器也是一种与SAX解析器也是有所不同的

SAX Parser会推送数据,但StAX解析器会从XML中提取所需的数据。StAX解析器将光标维持在文档中的当前位置,允许提取光标处可用的内容,而SAX解析器在遇到某些数据时发出事件。

XMLInputFactory和XMLStreamReader是可用于加载XML文件的两个类。当我们使用XMLStreamReader读取XML文件时,事件以整数值的形式生成,然后将这些事件与XMLStreamConstants中的常量进行比较。以下代码显示了如何使用StAX解析器解析XML:

import java.util.ArrayList;
import java.util.List;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;
 
public class StaxParserDemo {
  public static void main(String[] args) throws XMLStreamException {
    List<Employee> empList = null;
    Employee currEmp = null;
    String tagContent = null;
    XMLInputFactory factory = XMLInputFactory.newInstance();
    XMLStreamReader reader =
        factory.createXMLStreamReader(
        ClassLoader.getSystemResourceAsStream("xml/employee.xml"));
         
    while(reader.hasNext()){
      int event = reader.next();
      switch(event){
        case XMLStreamConstants.START_ELEMENT:
          if ("employee".equals(reader.getLocalName())){
            currEmp = new Employee();
            currEmp.id = reader.getAttributeValue(0);
          }
          if("employees".equals(reader.getLocalName())){
            empList = new ArrayList<>();
          }
          break;
           
        case XMLStreamConstants.CHARACTERS:
          tagContent = reader.getText().trim();
          break;
           
        case XMLStreamConstants.END_ELEMENT:
          switch(reader.getLocalName()){
            case "employee":
              empList.add(currEmp);
              break;
            case "firstName":
              currEmp.firstName = tagContent;
              break;
            case "lastName":
              currEmp.lastName = tagContent;
              break;
            case "location":
              currEmp.location = tagContent;
              break;
          }
          break;
        case XMLStreamConstants.START_DOCUMENT:
          empList = new ArrayList<>();
          break;
      }
 
    }
    for ( Employee emp : empList){
      System.out.println(emp);
    }
       
  }
}
 
class Employee{
  String id;
  String firstName;
  String lastName;
  String location;
   
  @Override
  public String toString(){
    return firstName+" "+lastName+"("+id+") "+location;
  }
}

输出结果为:

Rakesh Mishra(111) Bangalore
John Davis(112) Chennai
Rajesh Sharma(113) Pune

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