Canonicalizing and Hashing XML in Java

XmlHash.java

import org.apache.xml.security.Init;
import org.apache.xml.security.c14n.Canonicalizer;
import org.apache.xml.security.exceptions.XMLSecurityException;

import javax.xml.transform.OutputKeys;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.StringReader;
import java.security.GeneralSecurityException;
import java.security.MessageDigest;
import java.util.Base64;

public class XmlHash {

	static {
		Init.init();
	}

	public static void main(String... args) throws Exception {
		hash("<hello>world</hello>");
		hash("<hello>world<!-- yo --></hello>");
		hash("<hello>welt</hello>");
	}

	private static void hash(String xml) throws TransformerException, XMLSecurityException, IOException, GeneralSecurityException {

		var transformer = TransformerFactory.newDefaultInstance().newTransformer();
		var transformed = new ByteArrayOutputStream();
		transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
		transformer.setOutputProperty(OutputKeys.METHOD, "xml");
		transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
		transformer.transform(new StreamSource(new StringReader(xml)), new StreamResult(transformed));

		var canonicalizer = Canonicalizer.getInstance(Canonicalizer.ALGO_ID_C14N_EXCL_OMIT_COMMENTS);
		var canonicalized = new ByteArrayOutputStream();
		canonicalizer.canonicalize(transformed.toByteArray(), canonicalized, true);

		var digester = MessageDigest.getInstance("SHA-256");
		var digested = digester.digest(canonicalized.toByteArray());

		System.out.println(Base64.getEncoder().encodeToString(digested));
	}
}