How to Format an Unformatted XML String in Java Using JAXP and DOM?

Formatting an XML String in Java

As a Java developer, you may encounter situations where you have an XML string with no line feeds or indentations and need to convert it into a nicely formatted string. This is particularly useful for debugging purposes or presenting XML data in a readable manner.

To accomplish this task, you can leverage the Java API for XML Processing (JAXP) and the Document Object Model (DOM) to transform the XML string into a formatted representation.

Firstly, create a new Transformer object from the TransformerFactory. Set the "INDENT" and "{http://xml.apache.org/xslt}indent-amount" properties to "yes" and "2" respectively, to enable line breaks and indentations:

Transformer transformer = TransformerFactory.newInstance().newTransformer();
transformer.setOutputProperty(OutputKeys.INDENT, "yes");
transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2");

Next, convert the XML string into a DOMSource object:

String inputXml = "<tag><nested>hello</nested></tag>";
DOMSource source = new DOMSource(DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(new InputSource(new StringReader(inputXml))));

Then, create a StreamResult object to hold the formatted XML string:

StreamResult result = new StreamResult(new StringWriter());

Finally, transform the source DOM into the formatted XML string using the transformer:

transformer.transform(source, result);

The result.getWriter() object will contain the formatted XML string:

String formattedXml = result.getWriter().toString();

Example:

String unformattedXml = "hello";
Transformer transformer = TransformerFactory.newInstance().newTransformer();
transformer.setOutputProperty(OutputKeys.INDENT, "yes");
transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2");
DOMSource source = new DOMSource(DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(new InputSource(new StringReader(unformattedXml))));

StreamResult result = new StreamResult(new StringWriter());
transformer.transform(source, result);
System.out.println(result.getWriter().toString());

Output:

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

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