Re: method startElement() from class DOMLSParserFilter

Alberto Massari Fri, 04 Sep 2009 03:37:50 -0700

Hi Mirko,

I think the current implementation of the DOMLSParserFilter doesn't worknicely with your code, as the rejected nodes are not recycled and thememory will grow to the same level as before.

Anyhow, you should instead override acceptNode like this:


DOMParserFilter::FilterAction DOMParserFilter::acceptNode(DOMElement* node)
{
 // for element whose name is "DATA", skip it

if (node->getNodeType()==DOMNode::ELEMENT_NODE &&XMLString::compareString(node->getNodeName(), element_data)==0)

    return DOMParserFilter::FILTER_REJECT;
 else
   return DOMParserFilter::FILTER_ACCEPT;
}

Then, change DOMLSParserImpl::endElement to add a call toorigNode->release() after the call to removeChild().


Alberto


Mirko Braun wrote:

Hello everybody,

i would like to parse a quite large XML file (about 180 MB).
I used the DOM interface because i need the tree for further
processing of the data the xml file contains. Of course there
is a lot of memory used during parsing the file and i got an

"Out of memory" exception.

I noticed that a class DOMLSParserFilter comes along wiht Xercesc C++ 3.0.1 
(Win32), which makes it possible to filter the Nodes during parsing.
That is perfect for me because one XML-Element in my large file
contains most of the data. This XML-Element is called DATA and
appears serveral time in my XML file.
So i had the idea to reject this XML-Element from the DOM tree
during parsing to reduce the used memory by using the method
startElement() of the DOMLSParserFilter class. After that i would
use a SAX parser and just get all XML-Elements DATA with their values.
But it does not work.
I integregated my code into the DOMPrint example which comes along

with Xercesc C++ 3.0.1. The following error message occurred:

DOM Error during parsing: 
'C:\Daten\2009-08-07_NewXercesc\3_0_1\xerces-c-3.0.1\Build\Win32\VC6\Debug\MyXML.xml'
DOMException code is:  3
Message is: attempt is made to insert a node where it is not permitted


Did i misunderstand the functionality of the DOMLSParserFilter class
and its method startElement?
It is possible to realize my idea with the help of this class? Did
i something wrong with in my code (please have a look below)?

I would be very grateful for any help.

Thanks in advanced,
Mirko


DOMPrintFilter.hpp:
--------------------


class DOMParserFilter : public DOMLSParserFilter {
public:

  DOMParserFilter(DOMNodeFilter::ShowType whatToShow = DOMNodeFilter::SHOW_ALL);
    ~DOMParserFilter(){};

    virtual FilterAction startElement(DOMElement* node);
    virtual FilterAction acceptNode(DOMNode* node){return 
DOMParserFilter::FILTER_ACCEPT;};
    virtual DOMNodeFilter::ShowType getWhatToShow() const {return fWhatToShow;};

private:
    DOMNodeFilter::ShowType fWhatToShow;
};


DOMPrintFilter.cpp:
--------------------

DOMParserFilter::DOMParserFilter(DOMNodeFilter::ShowType whatToShow)
:fWhatToShow(whatToShow)
{}

DOMParserFilter::FilterAction DOMParserFilter::startElement(DOMElement* node)
{
  // for element whose name is "DATA", skip it
  if (XMLString::compareString(node->getNodeName(), element_data)==0)
    return DOMParserFilter::FILTER_REJECT;
  else
    return DOMParserFilter::FILTER_ACCEPT;
}


DOMPrint.cpp:
---------------

static const XMLCh gLS[] = { xercesc::chLatin_L, xercesc::chLatin_S, 
xercesc::chNull };

xercesc::DOMImplementation *implParser = 
xercesc::DOMImplementationRegistry::getDOMImplementation(gLS);

xercesc::DOMLSParser* parser = 
((xercesc::DOMImplementationLS*)implParser)->createLSParser(xercesc::DOMImplementationLS::MODE_SYNCHRONOUS,
 0);



DOMTreeErrorReporter *errReporter = new DOMTreeErrorReporter();
parser->getDomConfig()->setParameter(xercesc::XMLUni::fgDOMErrorHandler, 
errReporter);

DOMParserFilter * pDOMParserFilter = new DOMParserFilter();

parser->setFilter(pDOMParserFilter);

    //
    //  Parse the XML file, catching any XML exceptions that might propogate
    //  out of it.
    //
    bool errorsOccured = false;
    DOMDocument *doc = NULL;

    try
    {
      doc = parser->parseURI(gXmlFile);
    }
    catch (const OutOfMemoryException&)
    {
        XERCES_STD_QUALIFIER cerr << "OutOfMemoryException" << 
XERCES_STD_QUALIFIER endl;
        errorsOccured = true;
    }
    catch (const XMLException& e)
    {
        XERCES_STD_QUALIFIER cerr << "An error occurred during parsing\n   Message: 
"
             << StrX(e.getMessage()) << XERCES_STD_QUALIFIER endl;
        errorsOccured = true;
    }

    catch (const DOMException& e)
    {
      const unsigned int maxChars = 2047;
      XMLCh errText[maxChars + 1];

      XERCES_STD_QUALIFIER cerr << "\nDOM Error during parsing: '" << gXmlFile << 
"'\n"
           << "DOMException code is:  " << e.code << XERCES_STD_QUALIFIER endl;

      if (DOMImplementation::loadDOMExceptionMsg(e.code, errText, maxChars))
           XERCES_STD_QUALIFIER cerr << "Message is: " << StrX(errText) << 
XERCES_STD_QUALIFIER endl;

      errorsOccured = true;
    }

    catch (...)
    {
        XERCES_STD_QUALIFIER cerr << "An error occurred during parsing\n " << 
XERCES_STD_QUALIFIER endl;
        errorsOccured = true;
    }

Re: method startElement() from class DOMLSParserFilter

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