扩展标记语言(XML)是用于在不同应用程序之间进行消息传递和通信的流行媒介之一。
由于XML是开源的，并且可以通过DTD和XSD提供对数据格式的控制，因此它在各种技术中得到了广泛的使用。

Java XML格式化程序

几天前，我遇到了这样一种情况，即第三方API将Document对象和XML消息作为String返回。
因此，我编写了这个简单的XmlFormatter类，以使用适当的缩进来格式化XML，并将Document对象转换为XML String。

package com.theitroad.java.xmlutil;

import org.apache.xml.serialize.OutputFormat;
import org.apache.xml.serialize.XMLSerializer;
import org.w3c.dom.Document;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import java.io.IOException;
import java.io.StringReader;
import java.io.StringWriter;
import java.io.Writer;

/**
 * Utility Class for formatting XML
 * @author hyman
 *
 */
public class XmlFormatter {

	/**
	 *
	 * @param unformattedXml - XML String
	 * @return Properly formatted XML String
	 */
	public String format(String unformattedXml) {
		try {
			Document document = parseXmlFile(unformattedXml);

			OutputFormat format = new OutputFormat(document);
			format.setLineWidth(65);
			format.setIndenting(true);
			format.setIndent(2);
			Writer out = new StringWriter();
			XMLSerializer serializer = new XMLSerializer(out, format);
			serializer.serialize(document);

			return out.toString();
		} catch (IOException e) {
			e.printStackTrace();
			return "";
		}

	}

	/**
	 * This function converts String XML to Document object
	 * @param in - XML String
	 * @return Document object
	 */
	private Document parseXmlFile(String in) {
		try {
			DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
			DocumentBuilder db = dbf.newDocumentBuilder();
			InputSource is = new InputSource(new StringReader(in));
			return db.parse(is);
		} catch (ParserConfigurationException e) {
			throw new RuntimeException(e);
		} catch (SAXException e) {
			throw new RuntimeException(e);
		} catch (IOException e) {
			e.printStackTrace();
		}
		return null;
	}
	/**
	 * Takes an XML Document object and makes an XML String. Just a utility
	 * function.
	 *
	 * @param doc - The DOM document
	 * @return the XML String
	 */
	public String makeXMLString(Document doc) {
		String xmlString = "";
		if (doc != null) {
			try {
				TransformerFactory transfac = TransformerFactory.newInstance();
				Transformer trans = transfac.newTransformer();
				trans.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
				trans.setOutputProperty(OutputKeys.INDENT, "yes");
				StringWriter sw = new StringWriter();
				StreamResult result = new StreamResult(sw);
				DOMSource source = new DOMSource(doc);
				trans.transform(source, result);
				xmlString = sw.toString();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		return xmlString;
	}
	public static void main(String args[]){
		XmlFormatter formatter = new XmlFormatter();
		String book = "<?xml version=\"1.0\"?><catalog><book id=\"bk101\"><author>Gambardella, Matthew</author><title>XML Developers Guide</title><genre>Computer</genre><price>44.95</price><publish_date>2000-10-01</publish_date><description>An in-depth look at creating applications with XML.</description></book><book id=\"bk102\"><author>Ralls, Kim</author><title>Midnight Rain</title><genre>Fantasy</genre><price>5.95</price><publish_date>2000-12-16</publish_date><description>A former architect battles corporate zombies, an evil sorceress, and her own childhood to become queen of the world.</description></book></catalog>";
		System.out.println(formatter.format(book));
	}
}

要使用此类，您需要ApachexercesImpl.jar，可以从其下载。

上面类的输出是格式正确的XML字符串：

<?xml version="1.0" encoding="UTF-8"?>
<catalog>
<book id="bk101">
  <author>Gambardella, Matthew</author>
  <title>XML Developers Guide</title>
  <genre>Computer</genre>
  <price>44.95</price>
  <publish_date>2000-10-01</publish_date>
  <description>An in-depth look at creating applications with XML.</description>
</book>
<book id="bk102">
  <author>Ralls, Kim</author>
  <title>Midnight Rain</title>
  <genre>Fantasy</genre>
  <price>5.95</price>
  <publish_date>2000-12-16</publish_date>
  <description>A former architect battles corporate zombies, an evil
    sorceress, and her own childhood to become queen of the world.</description>
</book>
</catalog>

我希望您会发现该实用程序类有助于在Java中格式化XML并将XML转换为Document，反之亦然。

更新资料

自从我撰写本文以来已经有很多年了，java已经发展了很多，我们可以使用javax.xml.transformAPI轻松格式化XML字符串。

package com.theitroad.java.xmlutil;

import java.io.StringReader;
import java.io.StringWriter;

import javax.xml.transform.OutputKeys;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;

/**
 * Utility Class for formatting XML
 * 
 * @author hyman
 *
 */
public class XmlFormatter {

	public String format(String input) {
		return prettyFormat(input, "2");
	}

	public static String prettyFormat(String input, String indent) {
		Source xmlInput = new StreamSource(new StringReader(input));
		StringWriter stringWriter = new StringWriter();
		try {
			TransformerFactory transformerFactory = TransformerFactory.newInstance();
			Transformer transformer = transformerFactory.newTransformer();
			transformer.setOutputProperty(OutputKeys.INDENT, "yes");
			transformer.setOutputProperty(OutputKeys.DOCTYPE_PUBLIC, "yes");
			transformer.setOutputProperty("{https://xml.apache.org/xslt}indent-amount", indent);
			transformer.transform(xmlInput, new StreamResult(stringWriter));

			return stringWriter.toString().trim();
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}

	public static void main(String args[]) {
		XmlFormatter formatter = new XmlFormatter();
		String book = "<?xml version=\"1.0\"?><catalog><book id=\"bk101\"><author>Gambardella, Matthew</author><title>XML Developers Guide</title><genre>Computer</genre><price>44.95</price><publish_date>2000-10-01</publish_date><description>An in-depth look at creating applications with XML.</description></book><book id=\"bk102\"><author>Ralls, Kim</author><title>Midnight Rain</title><genre>Fantasy</genre><price>5.95</price><publish_date>2000-12-16</publish_date><description>A former architect battles corporate zombies, an evil sorceress, and her own childhood to become queen of the world.</description></book></catalog>";
		System.out.println(formatter.format(book));
	}
}

输出将与之前的输出相同，您应该使用此输出，而不是添加对任何第三方API的依赖关系。