Small modification to an XML document using StAX

Question

I'm currently trying to read in an XML file, make some minor changes (alter the value of some attributes), and write it back out again.

I have intended to use a StAX parser (javax.xml.stream.XMLStreamReader) to read in each event, see if it was one I wanted to change, and then pass it straight on to the StAX writer (javax.xml.stream.XMLStreamReader) if no changes were required.

Unfortunately, that doesn't look to be so simple - The writer has no way to take an event type and a parser object, only methods like writeAttribute and writeStartElement. Obviously I could write a big switch statement with a case for every possible type of element which can occur in an XML document, and just write it back out again, but it seems like a lot of trouble for something which seems like it should be simple.

Is there something I'm missing that makes it easy to write out a very similar XML document to the one you read in with StAX?

Answer 1

After a bit of mucking around, the answer seems to be to use the Event reader/writer versions rather than the Stream versions.

(i.e. javax.xml.stream.XMLEventReader and javax.xml.stream.XMLEventWriter)

See also http://www.devx.com/tips/Tip/37795, which is what finally got me moving.

Answer 2

StAX works pretty well and is very fast. I used it in a project to parse XML files which are up to 20MB. I don't have a thorough analysis, but it was definitely faster than SAX.

As for your question: The difference between streaming and event-handling, AFAIK is control. With the streaming API you can walk through your document step by step and get the contents you want. Whereas the event-based API you can only handle what you are interested in.

Answer 3

I know this is rather old question, but if anyone else is looking for something like this, there is another alternative: Woodstox Stax2 extension API has method:

XMLStreamWriter2.copyEventFromReader(XMLStreamReader2 r, boolean preserveEventData) 

which copies the currently pointed-to event from stream reader using stream writer. This is not only simple but very efficient. I have used it for similar modifications with success.

(how to get XMLStreamWriter2 etc? All Woodstox-provided instances implement these extended versions -- plus there are wrappers in case someone wants to use "basic" Stax variants, as well)