XOM and Canonical XML

Question

I'm making a java application that checks if a XML file is already Canonical or not using XOM.

In my tests I have the following file which is already Canonical.

<doc xmlns="http://example.com/default" xmlns:x="http://example.com/x">
  <a a1="1" a2="2">123</a>
  <b xmlns:y="http://example.com/y" a3="&quot;3&quot;" y:a1="1" y:a2="2"></b>
</doc>

Here it is the code when I load it again with XOM.

<?xml version="1.0"?>
<doc xmlns="http://example.com/default" xmlns:x="http://example.com/x">
  <a a1="1" a2="2">123</a>
  <b xmlns:y="http://example.com/y" a3="&quot;3&quot;" y:a1="1" y:a2="2" />
</doc>

As you can see it adds again xml tag and delete the closing tag </b> because the value of tag b is empty. I haven't got any problem with xml version tag but I don't know what to do to keep the closing tag </b> when I load the canonical document from file.

Answer 1

It looks like you are outputting the document with a XOM Serializer you need to use a XOM Canonicalizer to output your xml document and keep it Canonical

This gives the output:

<?xml version="1.0" encoding="UTF-8"?>
<doc xmlns="http://example.com/default" xmlns:x="http://example.com/x">
    <a a1="1" a2="2">123</a>
    <b a3="&quot;3&quot;" y:a1="1" y:a2="2" xmlns:y="http://example.com/y"/>
</doc>

The following example program will output your XML Cannonically to System.out using a XOM Canonicalizer

package com.foo.bar.xom;

import java.io.IOException;

import nu.xom.Builder;
import nu.xom.canonical.Canonicalizer;
import nu.xom.Document;
import nu.xom.ParsingException;
import nu.xom.Serializer;
import nu.xom.ValidityException;

public class App
{
    public static void main(String[] args) throws ValidityException, ParsingException, IOException
    {
        Builder builder = new Builder();
        //Serializer serializer = new Serializer(System.out);
        Canonicalizer canonicalizer = new Canonicalizer(System.out, Canonicalizer.EXCLUSIVE_XML_CANONICALIZATION);
        //this assumes to your xml document is on the classpath in this package as my.xml
        Document input = builder.build(App.class.getResourceAsStream("my.xml"), null);
        //serializer.write(input);
        canonicalizer.write(input);

    }
}