Hi Jiantan,
looking at your ideas, I wonder whether this approach is a good one
(though it is a valid one). Let me try to express my thoughts (slightly
unstructured):
- Is is really a good idea to expose the technologies we are using
internally to parse an XML document to the user. In other words, should
the user know and explicitely have to use classes that carry names that
are linked to a technology such as SAX or STaX ? Is there a way to make
this more transparent ?
- Would it be possible to layer the approaches ? Personally, I see the
main benefits of a STaX parser in the context of XML data binding that
it would be absolutely easy to restrict the scope of processing during
e.g. unmarshalling. In other words, within a biggish XML document
navigate to a (smaller) subset and only use this subset as the input for
unmarshalling. Such a layering could be achieved by creating an adapter
that sits between the StAX parser and the UnmarshalHandler (which
implements SAX ContentHandler), and translates STaX events into SAX
events. This way, we would avoid having to completely write a new
STaXUnmarshalHandler (and all the logic currently sitting in
UnmarshalHandler).
Werner
建坛林 wrote:
1.introduction
marshalling is the processing of convert a Object into xml(or other
structured) file, while unmarshalling is the reverse processing of
marshalling. This techonology is very useful in data binding and data
transfering.
Marshaller/Unmarshaller is the very object that responsible for doing
these work. For marshaller/unmarshaller to do the marshalling work, it
need the help of a xml parser. There are two kinds of xml parser
nowaday:one is based on dom model, the other is based on stream model.As
to the latter one, we got sax and stax. sax is a push parser, while stax
is a pull parser. I think castor's purpose of switching between the sax
and stax is to make castor more adaptive to different situations.
2.solution
i think the work should be done to the class Marshaller and
UnMarshaller in Castor source.
Make Marshaller.java,UnMarshller
.java upper class instead of final class
class Marshaller {
private int parserType;
Marshaller marshaller = new SAXMarshaller() ;
...
public static void marshal(Object obj,Writer writer);
public static void marshal(Object obj,int parserType);
public static void marshal(Object obj,Marshaller marshaller);
...
public void setMarshaller(Marshaller marshaller);
public Marshaller getMarshaller();
...
}
class UnMarshaller {
private int parserType;
UnMarshaller unMarshaller = new SAXUnMarshaller()
public Object unmarshal(InputSource in){
unMarshaller.unmarshal(in);
}
public Object unmarshal(InputSource in, int parserType);
public Object unmarshal(InputSource in,UnMarshaller unmarshaller);
...
public void setUnMarshaller(UnMarshaller unMarshaller);
public UnMarshaller getUnMarshaller();
...
}
this Un~/Marshaller keeps the common methods of SAXMarshaller and
StaxMarshaller,
default use a SAXMarshller in order to make the existed code
unchanged;we change the Marshaller by using the specific constructor and
setUn~/Marshaller method. In this case,
it's flexible to switch from sax to stax,vice versa. It seems this
pattern is much more like
the strategy pattern. we just abstract the algorithm of un~/Marshal. and
it's flexible to
switch between these algorithm.
the former Marshaller.java can be a SAXMarshller.java and
SAXUnMarshaller.java.
class SAXMarshaller extends Marshaller {
...
}
class SAXUnMarshaller extends UnMarshaller {
...
}
we can add by the following new Implementation of Marshaller
class StaxMarshaller implements Marshaller {
...
}
class StaxUnMarshaller implements UnMarshaller {
...
}
make MarshallingHandler ,UnMarshallingHandler upper class instead of
final class just like
we did to Marshaller,UnMarshller
the specific work we have to do is in implemented a new
StaxMarshallerHandler and StaxUnMarshallerHandler
to implement the Un~/Marshalling in stax way
class SAXMarshallingHandler extends MarshallingHandler {
}
class SAXUnMarshallingHandler extends UnMarshallingHandler {
}
class StaxMarshallingHandler extends MarshallingHandler {
}
class StaxUnMarshallingHandler extends UnMarshallingHandler {
}
And the specific implementation of StaxMarshallingHandler is associated
with how to map
a object to xml(and the reverse process).The detail of this can refer
the implementation
of StaxMarshallingHandler(former MarshallingHandler).
3.self-introduction
http://docs.google.com/Doc?docid=dc42tcq9_88gtxts6fv&hl=en
<http://docs.google.com/Doc?docid=dc42tcq9_88gtxts6fv&hl=en>
Jiantan Lin
2008/4/3, Werner Guttmann <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>>:
HI,
I have recently asked all the students that have submitted an
application to be mentored by one of the existing Castor committer
sto subscribe to this mailing list, so that we can ask questions
about their proposal and vice versa.
Can I please ask all students to introduce themselves briefly, and
once again describe their proposals. It's especially the benefits
for the project that I am personally interested in.
Thanks
Werner
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