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Re: StAX XMLStreamWriter Oddities

• To: "Xml-Dev" <xml-dev@l...>
• Subject: Re: StAX XMLStreamWriter Oddities
• From: "Karl Waclawek" <karl@w...>
• Date: Sat, 8 Nov 2003 11:32:01 -0500
• References: <005301c3a5f0$3475df20$6601a8c0@rainbow>

> Also, I noticed that there is a patent filed on StAX by the StAX spec lead:

> http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2F
> netahtml%2FPTO%2Fsearch-bool.html&r=1&f=G&l=50&co1=AND&d=PG01&s1=20030159112
> .PGNR.&OS=DN/20030159112&RS=DN/20030159112

What is so unique about StAX that it warrants a patent?
Can anyone enlighten me?

I looked at http://www.xml.com/pub/a/2003/09/17/stax.html, an
intro into StAX by Elliot Rusty Harold, and fail to see
any major breakthrough. Pull APIs have been around for a while,
and with the old MSXML 3.0 IMXeaderControl interface pull
parsing - like demonstrated with StAX - is easily possible
on top of SAX. Really, all you need is the capability
to interrupt/suspend a SAX parser, and then resume again.

The only "API" we need to define is a simple ParseEvent interface:
(I am not a Java programmer, so please forgive syntax errors)

  public interface ParseEvent {
    final int START_ELEMENT = 1;
    final int END_ELEMENT = 2;
    final int COMMENT = 3;
    final int PI = 4;
    <and so forth>
    int getEventType();
    XML Node getEventNode();
  }
where XMLNode (or rather a sub-class) exposes properties
appropriate to the event.

A Java adaption of IMXReaderControl could look like this:

public interface XMLReaderControl {
  final int READY = 0;      // status constant
  final int PARSING = 1;    // status constant
  final int SUSPENDED = 2;  // status constant
  void suspend();           // legal when PARSING
  void abort();             // legal when PARSING, SUSPENDED
  void resume();            // legal when SUSPENDED
  int getStatus();
}

The main pull parsing loop with a suspendable SAX parser could
then look like this, assuming the content handler implements
the ParseEvent interface described above and calls ReaderControl.suspend()
in the appropriate places:

   XMLReader.parse(inputSource);
   while (ReaderControl.getStatus() == SUSPENDED) {
     switch (ParseEvent.getEventType()) {
       case START_ELEMENT: 
         <cast getEventNode to ElementNode and process it>
         break;
       case END_ELEMENT:   
         <cast getEventNode to ElementNode and process it>
         break;
       case PI:           
         <cast getEventNode to PINode and process it>
         break;
       case COMMENT:      
         <cast getEventNode to CommentNode and process it>
         break;
       <and so forth>
     }
     ReaderControl.resume();
   }

One can likely implement a re-usable PullHandler class that
does most of the grunt work for that purpose. I would also
think of the ability to plug in an event filter class so
that one can iterate only over the events of interest.

I am not sure which streaming parser implement such suspend functionality,
I only know that Expat already has a patch (not part of the distro yet)
that achieves that. I don't think it should be a major problem to implement.

Karl

• References:
  • StAX XMLStreamWriter Oddities
    • From: "Don Park" <donpark@d...>

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