XML（可扩展标记语言）是一种用于存储和传输数据的标记语言。在Java中，有许多库和工具可用于处理和解析XML。本文将介绍一些常用的Java XML处理和解析方法，并提供代码示例。
一、DOM（文档对象模型）解析器
DOM解析器将整个XML文档加载到内存中，并将其表示为一个树形结构。这使得我们可以方便地遍历和操作XML文档。
示例代码：
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 DOMParserExample {
public static void main(String[] args) {
try {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.parse("input.xml");
document.getDocumentElement().normalize();
NodeList nodeList = document.getElementsByTagName("book");
for (int i = 0; i < nodeList.getLength(); i++) {
Node node = nodeList.item(i);
if (node.getNodeType() == Node.ELEMENT_NODE) {
Element element = (Element) node;
String title = element.getElementsByTagName("title").item(0).getTextContent();
String author = element.getElementsByTagName("author").item(0).getTextContent();
int year = Integer.parseInt(element.getElementsByTagName("year").item(0).getTextContent());
System.out.println("Book " + (i + 1) + ":");
System.out.println("Title: " + title);
System.out.println("Author: " + author);
System.out.println("Year: " + year);
System.out.println();
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
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二、SAX（简单API for XML）解析器
SAX解析器是一种事件驱动的解析器，它逐行读取XML文档，并在解析过程中触发相应的事件。相比DOM解析器，SAX解析器更节省内存，适用于处理大型XML文档。
示例代码：
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 SAXParserExample {
public static void main(String[] args) {
try {
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser saxParser = factory.newSAXParser();
DefaultHandler handler = new DefaultHandler() {
boolean isTitle = false;
boolean isAuthor = false;
boolean isYear = false;
@Override
public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
if (qName.equalsIgnoreCase("title")) {
isTitle = true;
} else if (qName.equalsIgnoreCase("author")) {
isAuthor = true;
} else if (qName.equalsIgnoreCase("year")) {
isYear = true;
}
}
@Override
public void characters(char[] ch, int start, int length) throws SAXException {
if (isTitle) {
System.out.println("Title: " + new String(ch, start, length));
isTitle = false;
} else if (isAuthor) {
System.out.println("Author: " + new String(ch, start, length));
isAuthor = false;
} else if (isYear) {
System.out.println("Year: " + Integer.parseInt(new String(ch, start, length)));
isYear = false;
}
}
};
saxParser.parse("input.xml", handler);
} catch (Exception e) {
e.printStackTrace();
}
}
}
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三、JAXB（Java Architecture for XML Binding）
JAXB是Java的一种标准XML绑定技术，它可以将XML文档转换为Java对象，以及将Java对象转换为XML文档。
示例代码：
import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import java.io.File;
public class JAXBExample {
public static void main(String[] args) {
try {
JAXBContext jaxbContext = JAXBContext.newInstance(Book.class);
Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
Book book = (Book) unmarshaller.unmarshal(new File("input.xml"));
System.out.println("Title: " + book.getTitle());
System.out.println("Author: " + book.getAuthor());
System.out.println("Year: " + book.getYear());
Marshaller marshaller = jaxbContext.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(book, System.out);
} catch (Exception e) {
e.printStackTrace();
}
}
}
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四、XPath
XPath是一种用于在XML文档中定位元素的语言。在Java中，我们可以使用XPath来解析和查询XML文档。
示例代码：
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
public class XPathExample {
public static void main(String[] args) {
try {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.parse("input.xml");
XPathFactory xPathFactory = XPathFactory.newInstance();
XPath xPath = xPathFactory.newXPath();
XPathExpression expression = xPath.compile("//book[year > 2000]");
NodeList nodeList = (NodeList) expression.evaluate(document, XPathConstants.NODESET);
for (int i = 0; i < nodeList.getLength(); i++) {
System.out.println("Book " + (i + 1) + ":");
System.out.println("Title: " + xPath.compile("title").evaluate(nodeList.item(i)));
System.out.println("Author: " + xPath.compile("author").evaluate(nodeList.item(i)));
System.out.println("Year: " + Integer.parseInt(xPath.compile("year").evaluate(nodeList.item(i))));
System.out.println();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
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总结：
本文介绍了Java中常用的XML处理和解析方法，包括DOM解析器、SAX解析器、JAXB和XPath。根据实际需求，我们可以选择适合的方法来处理和解析XML文档。以上示例代码可以帮助读者更好地理解和使用这些方法。
