Perl Requires Chilkat v9.5.0.80+

Efficiently Process a Huge XML File

See more XML Examples

Demonstrates a technique for processing a huge XML file (can be any size, even many gigabytes). Chilkat2 Perl

use strict;
use warnings;
use Chilkat2;

# This example shows a way to efficiently process a gigantic XML file -- one that may be too large
# to fit in memory.
#
# Two types of XML parsers exist: DOM parsers and SAX parsers.

# A DOM parser is a Document Object Model parser, where the entire XML is loaded into memory
# and the application has the luxury of interacting with the XML in a convenient, random-access
# way.  The Chilkat Xml class is a DOM parser.  Because the entire XML is loaded into memory,
# huge XML files (on the order of gigabytes) are usually not loadable for memory constraints.

# A SAX parser is such that the XML file is parsed as an input stream.  No DOM exists.
# Using a SAX parser is generally less palatable than using a DOM parser, for many reasons.
#
# The technique described here is a hybrid.  It streams the XML file as unstructured text
# to extract fragments that are individually treated as separate XML documents loaded into
# the Chilkat Xml parser.
#
# For example, imagine your XML file is several GBs in size, but has a relatively simple structure, such as:
#
# <Transactions>
#     <Transaction id="1">
#          ...
#     </Transaction>
#     <Transaction id="2">
#          ...
#     </Transaction>
#     <Transaction id="3">
#          ...
#     </Transaction>
# ...
# </Transactions>

# In the following code, each <Transaction ...> ... </Transaction>
# is extracted and loaded separately into an Xml object, where it can be manipulated
# independently.  The entire XML file is never entirely loaded into memory.

my $fac = Chilkat2::FileAccess->new;

my $success = $fac->OpenForRead('qa_data/xml/transactions.xml');
if (!$success) {
    print $fac->LastErrorText, "\n";
    exit;
}

my $xml = Chilkat2::Xml->new;
my $sb = Chilkat2::StringBuilder->new;
my $firstIteration = 1;
my $retval = 1;
my $numTransactions = 0;

# The begin marker is "XML tag aware".  If the begin marker begins with "<"
# and ends with ">", then it is assumed to be an XML tag and it will also match
# substrings where the ">" can be a whitespace char.
my $beginMarker = '<Transaction>';
my $endMarker = '</Transaction>';

while ($retval == 1) {
    $sb->Clear();
    # The retval can have the following values:
    # 0: No more fragments exist.
    # 1: Captured the next fragment.  The text from beginMarker to endMarker, including the markers, are returned in sb.
    # -1: Error.
    $retval = $fac->ReadNextFragment($firstIteration, $beginMarker, $endMarker, 'utf-8', $sb);
    $firstIteration = 0;

    if ($retval == 1) {
        $numTransactions = $numTransactions + 1;
        $success = $xml->LoadSb($sb, 1);
        # Your application may now do what it needs with this particular XML fragment...
    }
}

if ($retval < 0) {
    print $fac->LastErrorText, "\n";
}

print 'numTransactions: ', $numTransactions, "\n";