RE: structuring pull parsing code and using serializer [Re: [xmlpull-user] Java <-> XML using XMLPull]

Hi Alek,
 
1) I saw some CVS updates to XmlPullUtil.java but the file just had a
blank XmlPullUtil class. Just wanted to make sure I am not picking a
wrong version. When are you estimating to drop a workable version?
 
2) What is the difference between the two CVS repositories for XMLPull
API and addons:
               a) cvs.xmlpull.org:/l/extreme/cvspub
               b) cvs.extreme.indiana.edu:/l/extreme/cvspub
 
Thanks.
Naresh

	-----Original Message-----
	From: Aleksander Slominski [mailto:[email protected]] 
	Sent: Saturday, March 01, 2003 1:47 PM
	To: [email protected]
	Subject: Re: [xmlpull-dev] structuring pull parsing code and
using serializer [Re: [xmlpull-user] Java <-> XML using XMLPull]
	
	
	Naresh Bhatia wrote:
	
	> I have now worked extensively with XMLPull API and your
XmlPullWrapper 
	> - I love this stuff!
	
	hi Naresh,
	
	i am very happy to hear that :-)
	
	> I have tried several other approaches ranging from SAX all the
way to 
	> the latest data binding packages, but they all fell short of
my 
	> expectations. Some could not get the job done (especially when
it came 
	> to namespaces), others just did not present elegant solutions
(I am 
	> very picky about my designs and code :->). Anyway I am really 
	> impressed by the elegance of the XMLPull API and I have
decided to use 
	> it for my project.
	>  
	> In an effort to make the API even more easier to use, I have
the 
	> following suggestions. They are mainly directed at
XmlPullWrapper and 
	> your AddressBook example. I have refactored the code a little
to 
	> demonstrate how this approach could be used on larger
projects. My 
	> changes are attached along with an Ant build file.
	>  
	> - I have refactored the AddressBook example into 4 classes. 
	> MyAddressBook.java now contains only the main( ) method. The
read 
	> methods have been refactored into the AddressBookReader class
and the 
	> write methods have been moved to the AddressBookWriter class.
The 
	> Person class is now in its own seperate file as this is more
realistic 
	> on a real project.
	
	that looks reasonable and i would like to make it into a real
sample. 
	please take a look on this:
	
http://www.extreme.indiana.edu/~aslom/xml/databinding/jaxme-xmlpull/
	
	>  
	> - AddressBookReader inherits from XmlPullWrapper. This gives
me access 
	> to the parser in all methods - the parser is no longer passed
around 
	> in method signatures. In addition, I do not have to "create"
an 
	> XmlPullWrapper object whenever I need to use it - I am the 
	> XmlPullWrapper! This also resulted in more frequent use of the

	> XmlPullWrapper methods as they are more accessible!
	
	definitely that is one approach that can be taken and makes code
to read 
	address book very easy (just pass Reader)/
	
	however i would like to be able to pass parser instance to
address book 
	reader class as it allows for greater flexibility and makes
possible to 
	read multiple address books from one  XML input as parser can be
opened 
	once with XML input and then passed to any part of code that
needs it 
	(for example when address book XML is embedded in XML document i
can 
	scan for addreebook tag and then pass parser instance to
AddressBookReader)
	
	>  
	> - I added a class called XmlSerializerWrapper. The idea is
similar to 
	> XmlPullWrapper. This class holds convenience methods for 
	> XmlSerializer. Currently I have only one method in this class
called 
	> writeSimpleElement( ), which allows me to write simple
elements such 
	> as <username>johndoe</username> in one call.
	
	that is very good idea! defintely will add it.
	
	> - Added a method to XmlPullWrapper called
getRequiredElementText( ). 
	> This method allows you to read simple elements such as 
	> <username>johndoe</username> in one call.
	
	OK will add it.
	
	>  
	> - Fixed a minor bug in XmlPullWrapper.nextEndTag() - it was
going to 
	> the next start tag insted of the next end tag - probably a
cut&paste 
	> error from nextStartTag()  :-)
	
	OK will fix it.
	
	> - I would recommend that XmlPullWrapper and
XmlSerializerWrapper be 
	> supplied along with the XMLPull API - may be not as part of
the API 
	> but atleast as a supported utilities. This will encourage
people to 
	> use "best practices" and the wrappers will be thoroughly
tested. In 
	> addition, there will be only one standard version of the
wrappers 
	> instead of Alek's version and Naresh's version :-). Of course,
people 
	> are free to extend these utilities as they feel fit, but the
baseline 
	> is always the same.
	
	i agree - we need utilities and it is good idea to keep them
together in 
	one place. we have now place in XmlPull API CVS repository for
such 
	additions (that are called addons), see:
	
	http://www.xmlpull.org/v1/doc/addons.html
	http://www.xmlpull.org/viewcvs/~checkout~/xmlpull-api-v1/addons/
	
	after consulting with Stefan i was thinking about having
XmlPullUtil 
	class with only static methods and then have interface that
extends 
	XmlPullParser interface by adding useful methods (such as
nextEndTag) 
	and  there is implementation wrapper that uses JDK 1.3 dynamic
proxies 
	<http://java.sun.com/j2se/1.3/docs/guide/reflection/proxy.html>
to 
	automatically intercept calls and redirect them to parser impl
or 
	XMLUtil methods. that would work as follow:
	
	interface XmlPullWrapper extends XmlPullParser {
	   void nextEndTag(...)
	}
	
	
	the same for XmlSerializerWrapper, and then to actually create
instance 
	of wrapper:
	
	XmlPullWrapper pw = XmlPullDynamicProxy.newPullWrapper();
//default to 
	wrap parser created using default parser factory
	
	or with more control:
	
	// explicit wrapping that allows to wrap any instance of
XmlPullParser
	XmlPullParser pp = factory.newPullParser();
	//...
	XmlPullWrapper pw = XmlPullDynamicProxy.wrapparser);  
	
	then you can use wrapper exactly the same as XmlPullParser (as
it 
	extends XmlPullParser) *and * use additional methods so this
code would 
	work:
	
	pw.setInput()
	pw.next();
	pw.nextEndTag()
	
	this i think makes very nice use of built-in into XmlPull API 
	flexibility as it is based on factory and interfaces model so
can be 
	easily extended and XmlPullDynamicProxy is factory where
XmlPullWrapper  
	is extensions.
	
	if generalized enough this should allow to compose multiple
extensions 
	to XmlPullParser dynamically as in this case we have example of 
	interceptor based design (some people call it "lightweight" AOP)
	
	one thing to consider  is performance hit of using dynamic proxy
and i 
	plan to measure it comparing using dynamic proxy and 
	XmlPullutil/XmlPullParser directly.
	
	anyway those are my currentideas and i look forward to hear your
comments.
	
	> Here's the new main( ) function in MyAddressBook.java after
the 
	> refinements mentioned above. It is much more concise.
	>  
	>     public static void main (String args[])
	>     throws XmlPullParserException, IOException {
	>        
	>         System.out.println("reading address book from XML");
	>         AddressBookReader addressBookReader =
	>             new AddressBookReader(new
StringReader(SAMPLE_XML));
	
	>
	>         Vector addressBook =
addressBookReader.readAddressBook();
	>  
	>         //add new entry to address book
	>         addressBook.add(new Person("Foo Bar", "Silicon
Street"));
	>  
	>         System.out.println("serializing address book to XML");
	>         StringWriter sw = new StringWriter();
	>         AddressBookWriter addressBookWriter = new
AddressBookWriter(sw);
	>         addressBookWriter.writeAddressBook(addressBook);
	
	i would keep AddressBookReader/Writer stateless so they can be
reused so 
	it should allow setting input not only when it is created with
constructor
	
	>         System.out.println("Addressbook as XML:\n"+ sw);
	>     }
	> I would love to get your feedback on this stuff!
	
	i plan to drop Util and Wrapper classes into addons soon and
will add 
	your modifications.
	
	thanks,
	
	alek
	
	-- 
	"Mr. Pauli, we in the audience are all agreed that your theory
is crazy. 
	What divides us is whether it is crazy enough to be true." Niels
H. D. Bohr
	
	
	
	
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