Java中解析XML的方式有哪些

java解析XML的方式有使用DOM解析透過DOM物件以樹狀結構連接在一起；使用SAX 解析它是遇到不同元素時會逐行解析；使用StAX解析會從XML中提取所需的資料

XML是一種通用的資料交換格式,它的平台無關性、語言無關性、系統無關性、給資料整合與互動帶來了極大的方便。接下來將會在文章中為大家具體介紹在Java中解析XML的方式，具有一定的參考作用，希望對大家有所幫助

##【推薦課程：XML教學】

#使用DOM解析##DOM解析器主要用於在記憶體中使用XML作為物件圖（樹狀結構） 也就是文件物件模型（DOM）。首先解析器遍歷輸入XML檔案並建立與XML檔案中的節點相對應的DOM物件。這些DOM物件以樹狀結構連結在一起。一旦解析器完成了解析過程，就會從中得到這個類似樹的DOM物件結構。

範例：在所有程式碼範例中解析xml內容

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;
  }
}

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

SAX Parser與DOM解析器的不同之處在於SAX解析器不會將完整的XML載入到記憶體中，而是在遇到不同的元素時，它逐行解析XML，c觸發不同的事件，例如：開啟標記，結束標記，字元數據，評論等。

使用SAX Parser解析XML的程式碼如下：

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;
  }
}

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

#StAX用於XML的Streaming API，而StAX Parser與SA的不同之處在於SAX Parser。 StAX解析器也是一種與SAX解析器也是有所不同的

SAX Parser會推送數據，但StAX解析器會從XML中提取所需的數據。 StAX解析器將遊標維持在文件中的目前位置，允許提取遊標處可用的內容，而SAX解析器在遇到某些資料時發出事件。

XMLInputFactory和XMLStreamReader是兩個可用來載入XML檔案的類別。當我們使用XMLStreamReader讀取XML檔案時，事件會以整數值的形式生成，然後將這些事件與XMLStreamConstants中的常數進行比較。以下程式碼顯示如何使用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;
  }
}

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

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