java有一个静态方法U.formatXml(string)。生活的例子

import com.github.underscore.U;

public class MyClass {
    public static void main(String args[]) {
        String xml = "<tag><nested>hello</nested></tag>";

        System.out.println(U.formatXml("<?xml version=\"1.0\" encoding=\"UTF-8\"?><root>" + xml + "</root>"));
    }
}

输出:

<?xml version="1.0" encoding="UTF-8"?>
<root>
   <tag>
      <nested>hello</nested>
   </tag>
</root>

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();

}

我过去使用org.dom4j.io.OutputFormat.createPrettyPrint()方法打印过

public String prettyPrint(final String xml){  

    if (StringUtils.isBlank(xml)) {
        throw new RuntimeException("xml was null or blank in prettyPrint()");
    }

    final StringWriter sw;

    try {
        final OutputFormat format = OutputFormat.createPrettyPrint();
        final org.dom4j.Document document = DocumentHelper.parseText(xml);
        sw = new StringWriter();
        final XMLWriter writer = new XMLWriter(sw, format);
        writer.write(document);
    }
    catch (Exception e) {
        throw new RuntimeException("Error pretty printing xml:\n" + xml, e);
    }
    return sw.toString();
}

我用Scala看到了一个答案，所以这里有另一个用Groovy的答案，以防有人觉得有趣。默认缩进为2步，XmlNodePrinter构造函数也可以传递另一个值。

def xml = "<tag><nested>hello</nested></tag>"
def stringWriter = new StringWriter()
def node = new XmlParser().parseText(xml);
new XmlNodePrinter(new PrintWriter(stringWriter)).print(node)
println stringWriter.toString()

如果groovy jar在类路径中，则使用Java

  String xml = "<tag><nested>hello</nested></tag>";
  StringWriter stringWriter = new StringWriter();
  Node node = new XmlParser().parseText(xml);
  new XmlNodePrinter(new PrintWriter(stringWriter)).print(node);
  System.out.println(stringWriter.toString());

以上所有的解决方案都不适合我，然后我找到了这个http://myshittycode.com/2014/02/10/java-properly-indenting-xml-string/

线索就是用XPath删除空格

    String xml = "<root>" +
             "\n   " +
             "\n<name>Coco Puff</name>" +
             "\n        <total>10</total>    </root>";

try {
    Document document = DocumentBuilderFactory.newInstance()
            .newDocumentBuilder()
            .parse(new InputSource(new ByteArrayInputStream(xml.getBytes("utf-8"))));

    XPath xPath = XPathFactory.newInstance().newXPath();
    NodeList nodeList = (NodeList) xPath.evaluate("//text()[normalize-space()='']",
                                                  document,
                                                  XPathConstants.NODESET);

    for (int i = 0; i < nodeList.getLength(); ++i) {
        Node node = nodeList.item(i);
        node.getParentNode().removeChild(node);
    }

    Transformer transformer = TransformerFactory.newInstance().newTransformer();
    transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
    transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
    transformer.setOutputProperty(OutputKeys.INDENT, "yes");
    transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "4");

    StringWriter stringWriter = new StringWriter();
    StreamResult streamResult = new StreamResult(stringWriter);

    transformer.transform(new DOMSource(document), streamResult);

    System.out.println(stringWriter.toString());
}
catch (Exception e) {
    e.printStackTrace();
}

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。)