Java XML Pretty Print with Commented blocks - pretty-print

Question

I have below code to pretty print a given XML.
public void prettyPrintXML(String xmlString) {
try {
Source xmlInput = new StreamSource(new StringReader(xmlString));
StringWriter stringWriter = new StringWriter();
StreamResult xmlOutput = new StreamResult(stringWriter);
TransformerFactory transformerFactory = TransformerFactory.newInstance();
Transformer transformer = transformerFactory.newTransformer();
transformer.setOutputProperty(OutputKeys.METHOD, "xml");
transformer.setOutputProperty(OutputKeys.INDENT, "yes");
transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "4");
transformer.transform(xmlInput, xmlOutput);
System.out.println("OutPutXML : ");
System.out.println(xmlOutput.getWriter().toString());
} catch (Exception e) {
e.printStackTrace();
}
}
Here is an input and output of the above code:
InputXML :
<employees><employee><name>John</name><age>18</age></employee><!--employee><name>Smith</name><age>27</age></employee--></employees>
OutPutXML :
<?xml version="1.0" encoding="UTF-8"?>
<employees>
<employee>
<name>John</name>
<age>18</age>
</employee>
<!--employee><name>Smith</name><age>27</age></employee-->
</employees>
I need to get the commented block in above output in below format
<!--employee>
<name>Smith</name>
<age>27</age>
</employee-->
Is there a way to do this in Java without using any external libraries?

Answer 1

No, this is not supported out of the box using the standard libraries. Getting that kind of behaviour requires tweaking a lot; parsing the comment as XML and inheriting the indentation level from the parent node. You also run the risk of mixing comments containing plain text with those containing XML.
I have however implemented such a processor: xmlformatter. It also handles XML in text and CDATA nodes, and can do so robustly (i.e. does not fail on invalid XML within comments).
From
<parent><child><!--<comment><xml/></comment>--></child></parent>
you'll get
<parent>
<child>
<!--
<comment>
<xml/>
</comment>-->
</child>
</parent>
which I think will be a bit more readable than your desired output.