My first proposal on SoC project "Add support for the StAX (JSR-173) cursor API

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My first proposal on SoC project "Add support for the StAX (JSR-173) cursor API

My first proposal on SoC project "Add support for the StAX (JSR-173) cursor API

2007-03-31 - By wei duan

Hello，Everyone,

I'm a student applying for SoC
<http://code.google.com/soc/>projectAdd support for the StAX(JSR-173)
cursor API to Xerces-J<http://wiki.apache.org/general/SummerOfCode2007>.
Michael suggested I could discuss my proposal in the mailing list. So I
would like to introduce my thoughts and plan on this student project, any
comments are welcomed. : )

The abstract description of project is: "To design and implement the
cursor-based XMLStreamReader<http://java.sun.com/javase/6/docs/api/javax/xml
/stream/XMLStreamReader.html>(and
[image:
[WWW]] filtering<http://java.sun.com/javase/6/docs/api/javax/xml/stream
/StreamFilter.html>support).
It should be possible to accomplish this using
XNI <http://xerces.apache.org/xerces2-j/xni.html> by building the
XMLStreamReader<http://java.sun.com/javase/6/docs/api/javax/xml/stream
/XMLStreamReader.html>on
top of anXMLPullParserConfiguration<http://xerces.apache.org/xerces2-j/javadocs
/xni/org/apache/xerces/xni/parser/XMLPullParserConfiguration.html>."

Besides XNI, there are several ways to implement StAX interface. For
example, parse the XML document as raw text and start from scratch,
including parsing characters, building token, and interpreting tokens, and
so on. Or to implement a converter from existing DOM or SAX interfaces.
However, after reading Xerces sources code, I found both SAX and DOM
implementations are based on XNI, so it's very natural to build StAX on XNI.

To implement XMLStreamReader, two important preconditions should be
confirmed.

1. XML event information can be received.

2. The pull style parsing process can be simulated.

When I look through the XNI interfaces, I found it actually meets these two
preconditions. The handler interfaces in XNI such as XMLDocumentHandler and
XMLDTDHandler can get XML events including startDocument and endDocument,
which can be easily mapped to StAX events accordingly.
XMLPullParserConfiguration<http://xerces.apache.org/xerces2-j/javadocs/xni/org
/apache/xerces/xni/parser/XMLPullParserConfiguration.html>interface
in XNI is used to represent a parser configuration that can be
used as the configuration for a "pull" parser, thus the pull parsing process
of StAX can be simulated by calling "boolean parse(boolean)" method in
XMLPullParserConfiguration<http://xerces.apache.org/xerces2-j/javadocs/xni/org
/apache/xerces/xni/parser/XMLPullParserConfiguration.html>
.

Then I looked through the current Xerces Implementation, I found
AbstractXMLDocumentParser class implements XMLDocumentHandler,
XMLDTDHandler, and XMLDTDContentModelHandler interfaces. Both
AbstractDOMParser and AbstractSAXParser extend from
AbstractXMLDocumentParser. So I think I can implement an AbstractStAXParser
extending AbstractXMLDocumentParser to get XML events.

For example, code in current AbstractSAXParser:

* public void comment(XMLString text, Augmentations augs) throws
XNIException { *

* try {*

* // SAX2 extension*

* if (fLexicalHandler != null) {*

* fLexicalHandler.comment(text.ch, 0, text.length);*

* }*

* }*

* catch (SAXException e) {*

* throw new XNIException(e);*

* }*

* } // comment(XMLString)*

And in my AbstractStAXPaser, it may be implemented like this,

* public class AbstractStAXParser extends AbstractXMLDocumentParser {*

* public int m_curEventType;*

* public String m_characters;*

* ….*

* public void comment(XMLString text, Augmentations augs) throws
XNIException {*

* m_curEventType = XMLStreamConstants.COMMENT;*

* m_characters = new String(text.ch, text.offset, text.length);
*

* }*

* … *

* }*

*
*

Meanwhile, XMLPullParserConfiguration<http://xerces.apache.org/xerces2-j
/javadocs/xni/org/apache/xerces/xni/parser/XMLPullParserConfiguration.html>will
be used to control the parsing process. XML11Configuration is the
implementation of XMLPullParserConfiguration interface in Xerces. I think I
can implement StAXPaserConfiguration which extends from XML11Configuration
for XML1.0 and XML 1.1. In runtime, AbstractStAXParser will be set as the
handlers of the StAXParserConfiguration instance.

As for XMLStreamReader, it can be implemented as this,

*public class StAXXMLStreamReaderr implements XMLStreamReader {*

* public StAXPaserConfiguration m_configuration;*

* public StAXParser m_parser;*

* ….*

* int getEventType<http://java.sun.com/javase/6/docs/api/javax/xml/stream
/XMLStreamReader.html#getEventType%28%29>
()*

*{*

* return m_parser.m_curEventType;*

* }
*

*int next<http://java.sun.com/javase/6/docs/api/javax/xml/stream
/XMLStreamReader.html#getEventType%28%29>
()*

*{*

* m_configuration.parse(false)*

*return m_parser.m_curEventType;;*

*}*

*… *

*}*

Above are some of my rough thoughts, so if you have any comments and
questions, I would like to discuss with you.

Thanks, Wei

Hello，Everyone,

      
I'm a student applying for <a href="http://code.google.com/soc/"
target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">SoC </a
>project
<a href="http://wiki.apache.org/general/SummerOfCode2007" target="_blank"
onclick="return top.js.OpenExtLink(window,event,this)"> Add support for the
StAX(JSR-173) cursor API to Xerces-J</a>.
Michael suggested I could discuss my
proposal in the mailing list. So I would like to introduce my thoughts and plan
on
this student project, any comments are welcomed. : ) <ins cite="mailto:home" datetime="2007-03
-31T14:27">
</ins>

        The abstract description
of project is: "To
design and implement the cursor-based<a href="http://java.sun.com/javase/6/docs
/api/javax/xml/stream/XMLStreamReader.html" target="_blank" onclick="return top
.js.OpenExtLink(window,event,this)">

XMLStreamReader</a>
(and <a href="http://java.sun.com/javase/6/docs/api/javax/xml/stream
/StreamFilter.html" target="_blank" onclick="return top.js.OpenExtLink(window
,event,this)">
<img alt="[WWW]" border="0" height="11" width="11">
filtering
</a>
support). It should be possible to accomplish this using <a href="http://xerces
.apache.org/xerces2-j/xni.html" target="_blank" onclick="return top.js
.OpenExtLink(window,event,this)">

XNI</a>
by building the <a href="http://java.sun.com/javase/6/docs/api/javax/xml/stream
/XMLStreamReader.html" target="_blank" onclick="return top.js.OpenExtLink(window
,event,this)">

XMLStreamReader</a>
on top of an<a href="http://xerces.apache.org/xerces2-j/javadocs/xni/org/apache
/xerces/xni/parser/XMLPullParserConfiguration.html" target="_blank" onclick=
"return top.js.OpenExtLink(window,event,this)">

XMLPullParserConfiguration</a>."


Besides XNI, there
are several ways to implement StAX interface. For example, parse the XML
document
as raw text and start from scratch, including parsing characters, building
token, and interpreting tokens, and so on. Or to implement a converter from
existing
DOM or SAX interfaces. However, after reading Xerces sources code, I found both
SAX and DOM implementations are based on XNI, so it's very natural to build
StAX on XNI.     

To
implement
XMLStreamReader, two important preconditions should be confirmed.

1.

     
XML event
information can be received.

2.

     
The pull style
parsing process can be simulated. 

When
I look
through the XNI interfaces, I found it actually meets these two preconditions.
The
handler interfaces in XNI such as XMLDocumentHandler and XMLDTDHandler can get
XML events including startDocument and endDocument, which can be easily mapped
to StAX events accordingly. <a href="http://xerces.apache.org/xerces2-j
/javadocs/xni/org/apache/xerces/xni/parser/XMLPullParserConfiguration.html"
title="interface in org.apache.xerces.xni.parser" target="_blank" onclick=
"return top.js.OpenExtLink(window,event,this)">

XMLPullParserConfiguration</a>
interface in XNI is used to represent a parser configuration that can be used
as the configuration for a "pull" parser, thus the pull parsing
process of StAX can be simulated by calling "boolean parse(boolean)"
method in <a href="http://xerces.apache.org/xerces2-j/javadocs/xni/org/apache
/xerces/xni/parser/XMLPullParserConfiguration.html" title="interface in org
.apache.xerces.xni.parser" target="_blank" onclick="return top.js.OpenExtLink
(window,event,this)">

XMLPullParserConfiguration</a>
 .  


Then
I looked
through the current Xerces Implementation, I found AbstractXMLDocumentParser
class implements XMLDocumentHandler, XMLDTDHandler, and
XMLDTDContentModelHandler
interfaces. Both AbstractDOMParser and AbstractSAXParser extend from
AbstractXMLDocumentParser.
So I think  I can implement an AbstractStAXParser extending
AbstractXMLDocumentParser to get XML events. 

For
example, code
in current AbstractSAXParser:

   
public void
comment(XMLString text, Augmentations augs) throws XNIException { 

   
     try {

   
         //
SAX2 extension

   
         if
(fLexicalHandler != null) {

   
            
fLexicalHandler.comment(text.ch, 0, text.length);

   
         }

   
     }

   
     catch
(SAXException e) {

   
        
throw new XNIException(e);

   
     }
    } //
comment(XMLString)

 

And in
my AbstractStAXPaser, it may be implemented like this, 
   public class AbstractStAXParser extends
AbstractXMLDocumentParser
{

   
     public int
m_curEventType;

        public String m_characters;

   &nbsp
;   ….

   
    public void
comment(XMLString text, Augmentations augs) throws XNIException {

   
           m
_curEventType
= XMLStreamConstants.COMMENT;

   
           m_characters
= new String(text.ch, text.offset, text.length); 

   &nbsp
;   }

   &nbsp
;  … 

  }
 
Meanwhile, <a href="http://xerces.apache.org/xerces2-j/javadocs/xni/org/apache
/xerces/xni/parser/XMLPullParserConfiguration.html" title="interface in org
.apache.xerces.xni.parser" target="_blank" onclick="return top.js.OpenExtLink
(window,event,this)">

XMLPullParserConfiguration</a>
will be used to control the parsing process. XML11Configuration is the
implementation
of XMLPullParserConfiguration interface in Xerces. I think I can implement
StAXPaserConfiguration which extends from XML11Configuration for XML1.0 and XML
1.1. In runtime, AbstractStAXParser will be set as the handlers of the
StAXParserConfiguration
instance. 

As for
XMLStreamReader, it can be implemented as this, 

public class
StAXXMLStreamReaderr implements XMLStreamReader
{

   
    public StAXPaserConfiguration
m_configuration;

   
   public StAXParser
m_parser;

   &nbsp
;   ….

      int <a href="http://java.sun.com/javase/6/docs/api/javax
/xml/stream/XMLStreamReader.html#getEventType%28%29" target="_blank" onclick=
"return top.js.OpenExtLink(window,event,this)">

getEventType</a>
()

{

    return m_parser.m_curEventType;

    
} 

int <a href="http://java
.sun.com/javase/6/docs/api/javax/xml/stream/XMLStreamReader.html#getEventType%28
%29" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">

next</a>()

{

   
m_configuration.parse(false)

return m_parser.m
_curEventType;;

}

… 

}

     
    
   Above are some of my rough thoughts, so if you have any comments
and questions, I would like to discuss with you.
  

Thanks, Wei