我也有同样的问题，我用JTidy (http://jtidy.sourceforge.net/index.html)取得了巨大的成功。

例子:

Tidy t = new Tidy();
t.setIndentContent(true);
Document d = t.parseDOM(
    new ByteArrayInputStream("HTML goes here", null);

OutputStream out = new ByteArrayOutputStream();
t.pprint(d, out);
String html = out.toString();

I have found that in Java 1.6.0_32 the normal method to pretty print an XML string (using a Transformer with a null or identity xslt) does not behave as I would like if tags are merely separated by whitespace, as opposed to having no separating text. I tried using <xsl:strip-space elements="*"/> in my template to no avail. The simplest solution I found was to strip the space the way I wanted using a SAXSource and XML filter. Since my solution was for logging I also extended this to work with incomplete XML fragments. Note the normal method seems to work fine if you use a DOMSource but I did not want to use this because of the incompleteness and memory overhead.

public static class WhitespaceIgnoreFilter extends XMLFilterImpl
{

    @Override
    public void ignorableWhitespace(char[] arg0,
                                    int arg1,
                                    int arg2) throws SAXException
    {
        //Ignore it then...
    }

    @Override
    public void characters( char[] ch,
                            int start,
                            int length) throws SAXException
    {
        if (!new String(ch, start, length).trim().equals("")) 
               super.characters(ch, start, length); 
    }
}

public static String prettyXML(String logMsg, boolean allowBadlyFormedFragments) throws SAXException, IOException, TransformerException
    {
        TransformerFactory transFactory = TransformerFactory.newInstance();
        transFactory.setAttribute("indent-number", new Integer(2));
        Transformer transformer = transFactory.newTransformer();
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
        transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "4");
        StringWriter out = new StringWriter();
        XMLReader masterParser = SAXHelper.getSAXParser(true);
        XMLFilter parser = new WhitespaceIgnoreFilter();
        parser.setParent(masterParser);

        if(allowBadlyFormedFragments)
        {
            transformer.setErrorListener(new ErrorListener()
            {
                @Override
                public void warning(TransformerException exception) throws TransformerException
                {
                }

                @Override
                public void fatalError(TransformerException exception) throws TransformerException
                {
                }

                @Override
                public void error(TransformerException exception) throws TransformerException
                {
                }
            });
        }

        try
        {
            transformer.transform(new SAXSource(parser, new InputSource(new StringReader(logMsg))), new StreamResult(out));
        }
        catch (TransformerException e)
        {
            if(e.getCause() != null && e.getCause() instanceof SAXParseException)
            {
                if(!allowBadlyFormedFragments || !"XML document structures must start and end within the same entity.".equals(e.getCause().getMessage()))
                {
                    throw e;
                }
            }
            else
            {
                throw e;
            }
        }
        out.flush();
        return out.toString();
    }

有一个非常好的命令行XML实用程序叫做xmlstarlet(http://xmlstar.sourceforge.net/)，它可以做很多事情，很多人都在使用它。

您可以使用Runtime以编程方式执行此程序。然后读入格式化的输出文件。它具有比几行Java代码所能提供的更多选项和更好的错误报告。

下载xmlstarlet: http://sourceforge.net/project/showfiles.php?group_id=66612&package_id=64589

我把它们混合在一起，写了一个小程序。它从xml文件中读取并打印出来。而不是xzy给出你的文件路径。

    public static void main(String[] args) throws Exception {
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    dbf.setValidating(false);
    DocumentBuilder db = dbf.newDocumentBuilder();
    Document doc = db.parse(new FileInputStream(new File("C:/Users/xyz.xml")));
    prettyPrint(doc);

}

private static String prettyPrint(Document document)
        throws TransformerException {
    TransformerFactory transformerFactory = TransformerFactory
            .newInstance();
    Transformer transformer = transformerFactory.newTransformer();
    transformer.setOutputProperty(OutputKeys.INDENT, "yes");
    transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2");
    transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
    transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no");
    DOMSource source = new DOMSource(document);
    StringWriter strWriter = new StringWriter();
    StreamResult result = new StreamResult(strWriter);transformer.transform(source, result);
    System.out.println(strWriter.getBuffer().toString());

    return strWriter.getBuffer().toString();

}

如果使用第三方XML库是可行的，那么您可以使用一些比目前票数最高的答案所建议的要简单得多的方法。

它声明输入和输出都应该是字符串，所以这里有一个实用程序方法，用XOM库实现:

import nu.xom.*;
import java.io.*;

[...]

public static String format(String xml) throws ParsingException, IOException {
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    Serializer serializer = new Serializer(out);
    serializer.setIndent(4);  // or whatever you like
    serializer.write(new Builder().build(xml, ""));
    return out.toString("UTF-8");
}

我对它进行了测试，结果不依赖于JRE版本或类似的东西。要了解如何根据自己的喜好定制输出格式，请查看Serializer API。

这实际上比我想象的要长——需要一些额外的行，因为Serializer想要写入一个OutputStream。但是请注意，这里很少有用于实际XML处理的代码。

(这个答案是我对XOM的评估的一部分，在我关于替代dom4j的最佳Java XML库的问题中，XOM被建议作为一个选项。在dom4j中，您可以使用XMLWriter和OutputFormat轻松实现这一点。编辑:…正如mlo55的答案所示。)

嗯…面对这样的事情，这是一个已知的bug… 只需添加这个OutputProperty ..

transformer.setOutputProperty(OutputPropertiesFactory.S_KEY_INDENT_AMOUNT, "8");

希望这对你有所帮助……