FYI, perl's object system is not so hot, so if
you want to do any real OO programming (writing classes that use inheritance,
etc.) in perl, you should buy Damien Conway's book on object oriented
perl. It provides work arounds for many of the shortcomings in perl's
object system.
As for traversing the dom tree in perl, I've
included my code for how I did it (this code was initially based on some
sample code provided in the Xerces-Perl distribution). My program
defines a generic tree traversing subroutine that takes a DOM tree and a
reference to a subroutine as arguments. The tree traversing subroutine
then applies the referenced subroutine to each node of the tree (kind of like
the way perl's `map' construct is used to apply a block of code to every
element in a list). Anyway, the thing you'll be interested in is the
DOM_traverse( ) function.
Good luck,
-ted
---------------------------------------------
#!/usr/bin/perl -w
use strict;
use XML::Xerces;
use
Getopt::Long;
## INIT STUFF ##
our %OPTIONS;
my $USAGE =
<<EOU;
USAGE: $0 [-v=xxx][-n] file
Options:
-v=xxx Validation
scheme [always | never | auto*]
-n Enable namespace
processing. Defaults to off.
-s Enable schema
processing. Defaults to off.
* = Default if not provided explicitly
EOU
my $rc = GetOptions(\%OPTIONS, 'v=s', 'n',
's');
die $USAGE unless $rc;
die $USAGE unless
scalar @ARGV;
my $file = $ARGV[0];
-f $file or
die "File '$file' does not exist!\n";
my $namespace =
$OPTIONS{n} || 0;
my $schema = $OPTIONS{s} ||
0;
my $validate = $OPTIONS{v} || 'auto';
if (uc($validate) eq 'ALWAYS') {
$validate = $XML::Xerces::DOMParser::Val_Always;
} elsif
(uc($validate) eq 'NEVER') {
$validate =
$XML::Xerces::DOMParser::Val_Never;
} elsif (uc($validate) eq
'AUTO') {
$validate =
$XML::Xerces::DOMParser::Val_Auto;
} else
{
die("Unknown value for -v:
$validate\n$USAGE");
}
## END INIT ##
my $parser = XML::Xerces::DOMParser->new();
$parser->setValidationScheme
($validate);
$parser->setDoNamespaces
($namespace);
$parser->setCreateEntityReferenceNodes(1);
$parser->setDoSchema
($schema);
my $error_handler =
XML::Xerces::PerlErrorHandler->new();
$parser->setErrorHandler($error_handler);
eval {
$parser->parse(XML::Xerces::LocalFileInputSource->new($file))
};
myDie($@) if $@;
my $doc = $parser->getDocument();
my $rootEl =
$doc->getDocumentElement();
DOM_traverse($rootEl, \&printPretty);
exit(0);
sub DOM_traverse
{
my ($node, $subr, $dpth)
= @_;
$dpth ||= 0;
$subr->($node, $dpth) if ($subr);
my $kid = $node->getFirstChild;
while ( not $kid->isNull )
{
DOM_traverse($kid, $subr,
$dpth + 1);
$kid =
$kid->getNextSibling();
}
}
sub printPretty
{
my ($node, $dpth) =
@_;
# return if empty text node
return if ($node->getNodeName eq "#text"
&&
$node->getNodeValue =~ /^\s*$/);
my $indent = (" " x $dpth);
# print node name and value
print ($indent.$node->getNodeName."=".$node->getNodeValue."\n");
# return unless an element-node (cuz only elements
have attributes)
return unless
$node->isa('XML::Xerces::DOM_Element');
my %attrs =
$node->getAttributes->to_hash();
return unless (%attrs); # return if no
attributes
print "$indent <";
while (my
($name, $value) = each %attrs) {
print " $name=\"$value\"";
}
print
" >\n";
};
sub myDie
{
my $err = shift;
ref($err) and die $err->getMessage();
die $err;
}
__END__
----- Original Message -----
Sent: Thursday, April 18, 2002 8:24
PM
Subject: Need help traversing DOM tree
with xerces in Perl
I know there's got to be a way to do this, but I am
having a dismal time trying to just print each node
name
for an xml document. Can someone please
help? My program
is breaking at the point
marked by ***. It can't find auto?
What
does this mean?
Environment: Windows NT
ActiveState v5.6.1
Xerces v1.3.3 (also from ActiveState)
Also, if someone has an example of doing a tree traversal,
it
would be very helpful. I have done this
many times in Java,
but cannot seem to get the Perl
equivalent working. I am not
very familiar
with "object oriented" Perl.
Here's my program. Any help is appreciated.
PG
--------------------
#!c:/ActiveState/bin/Perl -w
use XML::DOM;
use
XML::Xerces;
$fullpath = "test.xml";
my $parser = new XML::Xerces::DOMParser;
$parser->setDoValidation(1);
$parser->parse(XML::Xerces::LocalFileInputSource->new($fullpath));
my $doc = $parser->getDocument();
# Get the root node
my $nodes =
$doc->getElementsByTagName("component");
my $len
= $nodes->getLength;
# Loop through children and print their children
for($i = 0; $i < $len; $i++) {
&printNode($doc, $nodes->item($i));
}
# Recursively go through the rest of the children
sub printNode {
my($local_doc) = $_[0];
my($pNode) = $_[1];
# Print
data from current node
my($name)
= $pNode->getNodeName();
print
"Name: $name\n";
my($cNodes) =
$pNode->getChildNodes();
my($clen) = $cNodes->getLength;
for($j = 0; $j < $clen; $j++) {
# *** Code
breaks here. Error is:
# Can't locate
auto/XML/Xerces/DOM_Text/item.al in @INC (@INC contains:
# C:/ActiveState/lib
C:/ActiveState/site/lib .) at print.pl line 39
if($cNodes->item($j)->getNodeType() ==
$XML::Xerces::DOM_NODE::ELEMENT_NODE) {
&printNode($local_doc,
$cNodes->item($j));
}
}
}
exit(0);
