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?

Answer 1

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.
 * 

 * eg.
 * 
 * String formattedXml = new XmlFormatter().format("hello");
 * 
 */
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 =
                "\n" +
                        "    \n" +
                        "        \n" +
                        "   \t\t\t\t\t         ECB\n\n\n\n\n" +
                        "        \n" +
                        "    \n\n\n\n\n" +
                        "";

        System.out.println(new XmlFormatter().format(unformattedXml));
    }

}