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From R J Scheuerle Jr <sc...@us.ibm.com>
Subject Re: Stax parsers - one more variation
Date Tue, 28 Jul 2009 13:35:58 GMT

FYI,

There were some gray areas in the StAX specification with regards to the
semantics of "set prefix".

In addition, there was an example in the specification that matched
XLXP-J's interpretation.


Thanks,


Rich Scheuerle
Senior Programmer, IBM Web Services
Development, Support, and Open Source
Apache Axis2 (scheu@apache.org)
512-286-8420  (IBM TL 363-8420)


                                                                           
             Andreas Veithen                                               
             <andreas.veithen@                                             
             gmail.com>                                                 To 
                                       commons-dev@ws.apache.org           
             07/28/2009 07:33                                           cc 
             AM                                                            
                                                                   Subject 
                                       Re: Stax parsers - one more         
             Please respond to         variation                           
             commons-dev@ws.ap                                             
                 ache.org                                                  
                                                                           
                                                                           
                                                                           
                                                                           




Dims,

I just stumbled over TUSCANY-1818. When reading this together with
WSCOMMONS-66 and WSCOMMONS-262, things become clearer. Apparently,
what happened is that in the first versions of XLXP-J, IBM didn't get
the StAX specs right and Axiom had to adapt to this, i.e. the vague
term "user community" actually refers to IBM! When they finally
recognized this problem, they introduced the
javax.xml.stream.XMLStreamWriter.isSetPrefixBeforeStartElement
property as an elegant way to rectify this without making too much
noise. Brilliant!

Andreas

On Tue, Jul 28, 2009 at 09:21, Andreas Veithen<andreas.veithen@gmail.com>
wrote:
> Dims,
>
> Actually I initially developed the idea to have the concept of a "StAX
> dialect" in Axiom when I saw this piece of code. I started to
> implement this feature when trying to solve the thread safety issue,
> but the aim is clearly to get rid of the isSetPrefixBeforeStartElement
> hack(s).
>
> I had a closer look at the code during the weekend, but I fail to see
> in which case we would actually need/have
> isSetPrefixBeforeStartElement == true. In my opinion, the StAX
> specifications don't leave enough room for the second interpretation
> (that setPrefix would apply to the next writeStartElement) [1]. Also,
> of all the StAX implementations I've seen, none expects this. Do you
> have any idea which "user community" "believes" this?
>
> Andreas
>
> [1] http://people.apache.org/~veithen/axiom/devguide/ch02.html#d0e69
>
> On Tue, Jul 28, 2009 at 00:45, Davanum Srinivas<davanum@gmail.com> wrote:
>> Andreas,
>>
>> Not sure if you have seen this already. There's some convoluted code
>> in org/apache/axiom/om/impl/util/OMSerializerUtil.java (method
>> isSetPrefixBeforeStartElement) which basically has a toggle based on
>> the parsers.
>>
>>            // Fallback: Toggle based on sun or woodstox implementation.
>>            NamespaceContext nc = writer.getNamespaceContext();
>>            ret = (nc == null ||
>>                    (nc.getClass().getName().indexOf("wstx") == -1 &&
>>                            nc.getClass().getName().indexOf("weblogic")
== -1 &&
>>                            nc.getClass().getName().indexOf("sun") ==
-1));
>>
>> The javadoc has more information:
>>
>>    /**
>>     * Unfortunately there is disagreement in the user community about
>> the semantics of setPrefix on
>>     * the XMLStreamWriter.  An example will explain the difference:
>> writer.startElement("a")
>>     * writer.setPrefix("pre", "urn://sample") writer.startElement("b")
>>     * <p/>
>>     * Some user communities (woodstox) believe that the setPrefix is
>> associate with the scope for
>>     * "a" and thus remains in scope until the end of a.  The basis
>> for this believe is
>>     * XMLStreamWriter javadoc (which some would argue is incomplete).
>>     * <p/>
>>     * Some user communities believe that the setPrefix is associated
>> with the "b" element. These
>>     * communities reference an example in the specification and
>> historical usage of SAX.
>>     * <p/>
>>     * This method will return true if the setPrefix is associated
>> with the next writeStartElement.
>>     *
>>     * @param writer
>>     * @return true if setPrefix should be generated before startElement
>>     */
>>
>> Can you please take a look?
>>
>> If we can find a way to totally remove the need for caching the
>> boolean after checking the xmlstreamwriter, that would be a big bonus.
>>
>> thanks,
>> dims
>>
>> --
>> Davanum Srinivas :: http://davanum.wordpress.com
>>
>

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