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();
}

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());

使用jdom2: http://www.jdom.org/

import java.io.StringReader;
import org.jdom2.input.SAXBuilder;
import org.jdom2.output.Format;
import org.jdom2.output.XMLOutputter;

String prettyXml = new XMLOutputter(Format.getPrettyFormat()).
                         outputString(new SAXBuilder().build(new StringReader(uglyXml)));

对于那些寻找快速和肮脏的解决方案的人——它不需要XML是100%有效的。例如，在REST / SOAP日志的情况下(你永远不知道其他人发送了什么;-))

我发现并改进了一个我在网上找到的代码剪辑，我认为这仍然是一个有效的可能的方法:

public static String prettyPrintXMLAsString(String xmlString) {
    /* Remove new lines */
    final String LINE_BREAK = "\n";
    xmlString = xmlString.replaceAll(LINE_BREAK, "");
    StringBuffer prettyPrintXml = new StringBuffer();
    /* Group the xml tags */
    Pattern pattern = Pattern.compile("(<[^/][^>]+>)?([^<]*)(</[^>]+>)?(<[^/][^>]+/>)?");
    Matcher matcher = pattern.matcher(xmlString);
    int tabCount = 0;
    while (matcher.find()) {
        String str1 = (null == matcher.group(1) || "null".equals(matcher.group())) ? "" : matcher.group(1);
        String str2 = (null == matcher.group(2) || "null".equals(matcher.group())) ? "" : matcher.group(2);
        String str3 = (null == matcher.group(3) || "null".equals(matcher.group())) ? "" : matcher.group(3);
        String str4 = (null == matcher.group(4) || "null".equals(matcher.group())) ? "" : matcher.group(4);

        if (matcher.group() != null && !matcher.group().trim().equals("")) {
            printTabs(tabCount, prettyPrintXml);
            if (!str1.equals("") && str3.equals("")) {
                ++tabCount;
            }
            if (str1.equals("") && !str3.equals("")) {
                --tabCount;
                prettyPrintXml.deleteCharAt(prettyPrintXml.length() - 1);
            }

            prettyPrintXml.append(str1);
            prettyPrintXml.append(str2);
            prettyPrintXml.append(str3);
            if (!str4.equals("")) {
                prettyPrintXml.append(LINE_BREAK);
                printTabs(tabCount, prettyPrintXml);
                prettyPrintXml.append(str4);
            }
            prettyPrintXml.append(LINE_BREAK);
        }
    }
    return prettyPrintXml.toString();
}

private static void printTabs(int count, StringBuffer stringBuffer) {
    for (int i = 0; i < count; i++) {
        stringBuffer.append("\t");
    }
}

public static void main(String[] args) {
    String x = new String(
            "<soap:Envelope xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\"><soap:Body><soap:Fault><faultcode>soap:Client</faultcode><faultstring>INVALID_MESSAGE</faultstring><detail><ns3:XcbSoapFault xmlns=\"\" xmlns:ns3=\"http://www.someapp.eu/xcb/types/xcb/v1\"><CauseCode>20007</CauseCode><CauseText>INVALID_MESSAGE</CauseText><DebugInfo>Problems creating SAAJ object model</DebugInfo></ns3:XcbSoapFault></detail></soap:Fault></soap:Body></soap:Envelope>");
    System.out.println(prettyPrintXMLAsString(x));
}

输出如下:

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <soap:Fault>
        <faultcode>soap:Client</faultcode>
        <faultstring>INVALID_MESSAGE</faultstring>
        <detail>
            <ns3:XcbSoapFault xmlns="" xmlns:ns3="http://www.someapp.eu/xcb/types/xcb/v1">
                <CauseCode>20007</CauseCode>
                <CauseText>INVALID_MESSAGE</CauseText>
                <DebugInfo>Problems creating SAAJ object model</DebugInfo>
            </ns3:XcbSoapFault>
        </detail>
    </soap:Fault>
  </soap:Body>
</soap:Envelope>

使用scala:

import xml._
val xml = XML.loadString("<tag><nested>hello</nested></tag>")
val formatted = new PrettyPrinter(150, 2).format(xml)
println(formatted)

如果你依赖scala-library.jar，你也可以在Java中这样做。它是这样的:

import scala.xml.*;

public class FormatXML {
    public static void main(String[] args) {
        String unformattedXml = "<tag><nested>hello</nested></tag>";
        PrettyPrinter pp = new PrettyPrinter(150, 3);
        String formatted = pp.format(XML.loadString(unformattedXml), TopScope$.MODULE$);
        System.out.println(formatted);
    }
}

PrettyPrinter对象是用两个整数构造的，第一个是最大行长，第二个是缩进步骤。