Add comment to DOM document

This is an example of how to add comments to a DOM Document. We have implemented a method, that is void prettyPrint(Document xml), in order to convert a DOM into a formatted XML String. Adding comments to a DOM Document implies that you should:

• Obtain a new instance of a DocumentBuilderFactory, that is a factory API that enables applications to obtain a parser that produces DOM object trees from XML documents.
• Set the parser produced so as not to validate documents as they are parsed, using setValidating(boolean validating) API method of DocumentBuilderFactory, with validating set to false.
• Create a new instance of a DocumentBuilder, using newDocumentBuilder() API method of DocumentBuilderFactory.
• Parse the FileInputStream with the content to be parsed, using parse(InputStream is) API method of DocumentBuilder. This method parses the content of the given InputStream as an XML document and returns a new DOM Document object.
• Get the Document Element using getDocumentElement() API method of Document.
• Create a new Comment, using createComment(String data) API method of Document.
• Get the parent node of the Document Element, and use insertBefore(Node newChild, Node refChild) API method of Node, for the parent node, to insert the comment before the specified child of the parent node.
• Call void prettyPrint(Document xml) method of the example. The method gets the xml Document and converts it into a formatted xml String, after transforming it with specific parameters, such as encoding. The method uses a Transformer, that is created using newTransformer() API method of TransformerFactory. The Transformer is used to transform a source tree into a result tree. After setting specific output properties to the transformer, using setOutputProperty(String name, String value) API method of Transformer, the method uses it to make the transformation, with transform(Source xmlSource, Result outputTarget) API method of Transformer. The parameters are the DOMSource with the DOM node and the result that is a StreamResult created from a StringWriter.

Let’s take a look at the code snippet that follows:  

package com.javacodegeeks.snippets.core;

import java.io.File;
import java.io.FileInputStream;
import java.io.StringWriter;
import java.io.Writer;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.Comment;
import org.w3c.dom.Document;
import org.w3c.dom.Element;

public class AddCommentToDOMDocument {
	
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("in.xml")));
		
		Element element = doc.getDocumentElement();
		Comment comment = doc.createComment("This is a comment");
		element.getParentNode().insertBefore(comment, element);
		
		prettyPrint(doc);
		
	}
	
	public static final void prettyPrint(Document xml) throws Exception {
		Transformer tf = TransformerFactory.newInstance().newTransformer();
		tf.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
		tf.setOutputProperty(OutputKeys.INDENT, "yes");
		Writer out = new StringWriter();
		tf.transform(new DOMSource(xml), new StreamResult(out));
		System.out.println(out.toString());
	}

}

Input:

<?xml version="1.0" encoding="UTF-8"?>
<rss version="2.0">
	<channel>
		<title>Java Tutorials and Examples</title>
		<item>
			<title><![CDATA[Java Tutorials]]></title>
			<link>http://www.javacodegeeks.com/</link>
		</item>
	</channel>
</rss>

Output:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!--This is a comment-->
<rss version="2.0">
	<channel>
		<title>Java Tutorials and Examples</title>
		<item>
			<title><![CDATA[Java Tutorials]]></title>
			<link>http://www.javacodegeeks.com/</link>
		</item>
	</channel>
</rss>

  
This was an example of how to add comments to a DOM Document in Java.

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