How to pretty print XML from Java?

Question

I have a Java String that contains XML, with no line feeds or indentations. I would like to turn it into a String with nicely formatted XML. How do I do this?

String unformattedXml = "<tag><nested>hello</nested></tag>"; String formattedXml = new [UnknownClass]().format(unformattedXml); 

Note: My input is a String. My output is a String.

(Basic) mock result:

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

Answer 1

Transformer transformer = TransformerFactory.newInstance().newTransformer(); transformer.setOutputProperty(OutputKeys.INDENT, "yes"); transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2"); // initialize StreamResult with File object to save to file StreamResult result = new StreamResult(new StringWriter()); DOMSource source = new DOMSource(doc); transformer.transform(source, result); String xmlString = result.getWriter().toString(); System.out.println(xmlString); 

Note: Results may vary depending on the Java version. Search for workarounds specific to your platform.

Answer 2

Here's an answer to my own question. I combined the answers from the various results to write a class that pretty prints XML.

No guarantees on how it responds with invalid XML or large documents.

package ecb.sdw.pretty;  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 java.io.IOException; import java.io.StringReader; import java.io.StringWriter; import java.io.Writer;  /**  * Pretty-prints xml, supplied as a string.  * <p/>  * eg.  * <code>  * String formattedXml = new XmlFormatter().format("<tag><nested>hello</nested></tag>");  * </code>  */ public class XmlFormatter {      public XmlFormatter() {     }      public String format(String unformattedXml) {         try {             final 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) {             throw new RuntimeException(e);         }     }      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) {             throw new RuntimeException(e);         }     }      public static void main(String[] args) {         String unformattedXml =                 "<?xml version=\"1.0\" encoding=\"UTF-8\"?><QueryMessage\n" +                         "        xmlns=\"http://www.SDMX.org/resources/SDMXML/schemas/v2_0/message\"\n" +                         "        xmlns:query=\"http://www.SDMX.org/resources/SDMXML/schemas/v2_0/query\">\n" +                         "    <Query>\n" +                         "        <query:CategorySchemeWhere>\n" +                         "   \t\t\t\t\t         <query:AgencyID>ECB\n\n\n\n</query:AgencyID>\n" +                         "        </query:CategorySchemeWhere>\n" +                         "    </Query>\n\n\n\n\n" +                         "</QueryMessage>";          System.out.println(new XmlFormatter().format(unformattedXml));     }  }