How to stream XML data using XOM?
- by Jonik
Say I want to output a huge set of search results, as XML, into a PrintWriter or an OutputStream, using XOM. The resulting XML would look like this:
<?xml version="1.0" encoding="UTF-8"?>
<resultset>
<result>
[child elements and data]
</result>
...
...
[1000s of result elements more]
</resultset>
Because the resulting XML document could be big (tens or hundreds of megabytes, perhaps), I want to output it in a streaming fashion (instead of creating the whole Document in memory and then writing that).
The granularity of outputting one <result> at a time is fine, so I want to generate one <result> after another, and write it into the stream. Assume there's already a method that helps with iterating the results and generating Element objects:
public nu.xom.Element getNextResult();
So I'd simply like to do something like this pseudocode (automatic flushing enabled, so don't worry about that) :
open stream/writer
write declaration
write start tag for <resultset>
while more results:
write next <result> element
write end tag for <resultset>
close stream/writer
I've been looking at Serializer, but the necessary methods, writeStartTag(Element), writeEndTag(Element), write(DocType) are protected, not public! Is there no other way than to subclass Serializer to be able to use those methods, or to manually write the start and end tags directly into the stream as Strings, bypassing XOM altogether? (The latter wouldn't be too bad in this simple example, but in the general case it would get quite ugly.)
Am I missing something or is XOM just not made for this?
With dom4j I could do this easily using XMLWriter - it has constructors that take a Writer or OutputStream, and methods writeOpen(Element), writeClose(Element), writeDocType(DocumentType) etc. Compare to XOM's Serializer where the only public write method is the one that takes a whole Document.
Please refrain from answering if you're not familiar with XOM! I specifically want to know if and how you can do this kind of streaming with that library. (This is related to my question about the best dom4j replacement where XOM is a strong contender.)
