How do I prevent a pair of XMLEvent[Reader|Writer] from splitting empty tags into start+end tags?

Question

Hello, everyone!

I have an understanding problem of how the following code works:

XMLInputFactory xif = XMLInputFactory.newFactory();
XMLOutputFactory xof = XMLOutputFactory.newFactory();

XMLEventReader reader = xif.createXMLEventReader(/* ... */);
XMLEventWriter writer = xof.createXMLEventWriter(/* ... */);

writer.add(reader);

The method writer.add([some reader]) reads all events from reader and writes them consequently. Sadly, following happens:

The input

<root><c/></root>

gets transformed to

<root><c><c/></root>

I know, from XML point of view, these are equal trees, but not for a human ;)

What can I do to get the same output?

FYI: I need a XMLEvent[Reader|Writer] pair later to filter "XML events".

Answer 1

According to the list of XMLEvents it seems like there is no way to make the distinction and it will indeed generate a StartElement and EndElement event. The consumer would need to optimize for the case when a StartElement is immediately followed by an EndElement.

This is apparently not the case of the XMLEventReader returned by the factory. If you want to optimize this behavior yourself, I see no other way than to do something like

• check what's the concrete XMLEventReader implementation returned by createXMLEventReader
• subclass the XMLEventReader implementation to optimize this case
• subclass XMLInputFactory and override createXMLEventReader to return an instance of your XMLEventReader subclass

If this sounds too complicated (or doesn't work), I would suggest that you go with a solution that uses XMLStreamWriter. This one has a dedicated method writeEmptyElement.

(Or you can give a try to my home-made pretty printer, it's based on XMLStreamWriter)

Answer 2

Unless I am mistaken, Woodstox can be configured to either produce empty tags (default), or not (so it'll always output start+end tag, even if there is no content). Since you can configure this for XMLStreamWriter, and you can then produce XMLEventWriter using that stream writer, it should work as expected.