Advanced XML connections

Question

Hey there!
I'm fairly new to Flex development so please excuse my
ignorance if I've just managed to miss some feature or API
completely!
My situation is this:
I wish to develop a program which will communicate with my
server via a high-performance XML connection using a (currently
proprietary, open-source later) binary XML format. Since I'm the
one who has been writing the code for it in Java I have full access
to the source to port to Flex/action-script. What I'm wondering is
what (if any) is the standard API for XML parsers
(readers/writers)? My format is a StAX ("pull") parser for XML
streams, and I have classes that allow me to use XPaths efficiently
over it.
I would like very much to make it using a standard Flex API,
extending where required to leverage additional features, as this
would be more useful I think in future when I release it as an
open-source project.
Further to this, I will be hoping to use this with an SSL
connection to keep data private, I am wondering if Flex already has
SSL functionality, and how fast it is?
Please don't dispute the use of binary XML here, since I'm
communicating between two parties then readability isn't an issue
(except debugging, in which case it's easy to output as text with a
third party, or by dropping in a regular XML reader/writer). For my
intended data-set I get around a 40-50% reduction in message size,
haven't tested relative performance compared to text-XML parsers,
but it should be faster since it doesn't need to do much work.
So I'm looking for an idea of what I should implement or
extend and what I will need to develop from scratch to make this
work? My aim is to develop this as an AIR application, but may
compile for browser as well since I have no major requirement for
local storage.
Cheers

Answer 1

Hmm, thanks for the response! While that looks like an
interesting way of manipulating XML, it appears to be DOM-based?
The method I'm hoping to implement is StAX or "pull" parsing. A
simple example (in Java) using my parser could look like this.
Note: I'm using hyphens in place of working tabs since there seems
to be no equivalent of <pre> on HTML here that I see:
Example XML:
<items>
- <category>Mixed</category>
- <item>Bread</item>
- <item>Monkey</item>
</items>
Java code (assuming an XMLStreamReader is positioned inside
the <items> tag:
int event;
while ((event = reader.next()) !=
XMLStreamConstants.END_DOCUMENT) {
- switch (event) {
- - case START_ELEMENT:
- - String name = reader.getLocalName();
- - if (name.equals("item"))
System.out.println("\t"+reader.getElementText());
- - else if (name.equals("category"))
System.out.println(reader.getElementText());
- - break;
The output of the above would appear (as the data arrives)
like:
Mixed
- Bread
- Monkey
Basically, unlike DOM which reads in all the XML and provides
you with a model you can then pull elements out from, a StAX parser
lets you tell the parser when to parse, it tells you what it found
and you can then decide what to do with that data. It's very good
for using as an XPath stream parser, as you can look for an XPath
match on an XML document hundreds of megabytes in size, without
ever using more than a few kilobytes of memory. Disadvantage of
course is that once you've passed an XML element, you can't go back
unless you saved it somewhere.
My XMLStreamReader is fairly easy to adapt into use as a DOM
parser as well, and it's pretty good at that too, but I try to
avoid DOM like the plague where possible.
If Flex only has DOM available then I would like port my
parser as a mirror image of the Java parser, and hope that any
future Flex StAX parser standard is similar enough to easily mash
my code into at that time.