man Data::Stag::BaseHandler (3): Base class for writing tag stream handlers

SYNOPSIS

# EXAMPLE 1
package MyPersonHandler;
use base qw(Data::Stag::BaseHandler);
# handler that prints <person> nodes as they are parsed;
# after each <person> node is intercepted, it is discarded
# (it does not go to form the final tree)
sub e_person {
my $self = shift;
my $node = shift;
printf "Person name:%s address:%s\n",
$node->sget('name'), $node->sget('address');
return; # prune this from tree
}
1;

# EXAMPLE 2
package MyStatsHandler;
use base qw(Data::Stag::BaseHandler);
# handler that modifies tree as it goes
# changes <measurement><unit>inch</unit><quantity>10</quantity></measurement>
# to <measurement><unit>cm</unit><quantity>25</quantity></measurement>
sub e_measurement {
my $self = shift;
my $node = shift;
if ($node->sget('unit') eq 'inch') {
$node->set('unit', 'cm');
$node->set('quantity', $node->get('quantity') * 2.5);
}
return $node; # replace <measurement> with new data in result tree
}
1;

# Using the handlers
my $handler = MyHandler->new;
my $stag = Data::Stag->parse(-fh=>$fh, -handler=>$handler);
# Using a handler from the command line:
unix> stag-handle.pl -m MyHandler input.xml > post-processed.xml

DESCRIPTION

Default Simple Event Handler, other handlers inherit from this class

See also Data::Stag and Data::Stag::BaseGenerator

Stag has an event-handling architecture; parsers or generators generate or fire events. Events can be hierarchical/nested, just like stag nodes. These events are caught by handlers. By default, uncaught events stack to form stag trees.

Stag has built in parsers for parsing xml, sxpr and itext data. You can construct your own parsers for dealing with your own formats specific to your own data; these should inherit from Data::Stag::BaseGenerator

Stag also has built in handlers for these formats. You can construct your own - either as modules that inherit from this one, or as hashes of anonymous subroutines.

If you wish to write your own handler that writes out to another format, you may wish to inherit from Data::Stag::Writer

CATCHING EVENTS

This class catches Data::Stag node events (start, end and body) and allows the subclassing module to intercept these. Unintercepted events get pushed into a tree. The final tree is returned at the end of a parse() call

This class can take SAX events and turn them into simple Data::Stag events

the events recognised are

  start_event(node-name)
  evbody(node-data)
  end_event(node-name)

and also

  event(node-name, node-data|[nodes])

which is just a wrapper for the other events

you can either intercept these methods; or you can define methods

  s_<element_name>
  e_<element_name>

that get called on the start/end of an event; you can dynamically change the structure of the tree by returning nodes from these methods.

  # the follow handler prunes <foo> nodes from the tree, and writes
  # out data from the <person> node
  # when parsing large datasets, it can be a good idea to prune nodes
  # from the tree, so the result tree of the parse is not too big
  my $h = Data::Stag->makehandler( foo => 0,
                                   person => sub {
                                       my $self = shift;
                                       my $node = shift;
                                       printf "Person name:%s address:%s\n",
                                         $node->sget('name'), $node->sget('address');
                                       return;
                                   });
  my $parser = MyParser->new;
  $parser->handler($h);
  $parser->parse(-fh=>$fh);
  my $result_tree = $h->stag;

PUBLIC METHODS -

new

       Title: new
        Args: 
      Return: L<Data::Stag::BaseHandler>
     Example:

returns the tree that was built from all uncaught events

tree (stag)

       Title: tree
     Synonym: stag
        Args: 
      Return: L<Data::Stag>
     Example: print $parser->handler->tree->xml;

returns the tree that was built from all uncaught events

CAUGHT EVENTS

A Data::Stag::BaseGenerator class will generate events by calling the following methods on this class:

start_event NODENAME
evbody DATA
end_event NODENAME {optional}
event NODENAME DATA

These events can be nested/hierarchical

If uncaught, these events are stacked into a stag tree, which can be written as xml or one of the other stag formats

PROTECTED METHODS -

s_*

        Args: handler L<Data::Stag::BaseHandler>
      Return: 
     Example:

autogenerated method - called by the parser when ever it starts a node; * matches the node name

override this class providing the name of the node you wish to intercept

e_*

        Args: handler L<Data::Stag::BaseHandler>, node L<Data::Stag>
      Return: node L<Data::Stag>
     Example:

autogenerated method - called by the parser when ever it ends a node; * matches the node name

override this class providing the name of the node you wish to intercept

CONSUMES

define this in your handler class to make explicit the list of node names that your parser consumes; this is then used if your handler is placed in a chain

  package MyHandler;
  use base qw(Data::Stag::BaseHandler);
  sub CONSUMES {qw(person city)}
  sub e_person {....}
  sub e_city   {....}

depth

       Title: depth
        Args: 
      Return: depth int
     Example:

depth of the nested event tree

       Title: up
        Args: dist int
      Return: node stag
     Example: $stag->up(-2);

when called when intercepting a node <foo>, this will look dist up the tree to find the container node

For example, if our data contains the node <blah> below:

  <blah>
    <foo>
      <a>1</b>
    </foo>
    <foo>
      <a>2</b>
    </foo>
  </blah>
    # and we have the following code:
    $h = Data::Stag->makehandler(foo=>sub {
                                           my ($self, $foo) = @_;
                                           print $foo->up(1)->xml;
                                           return});

The <foo> handler will be called twice; it will print the structure of the containing <blah> node, but the first time round, the <blah> node will not be complete

up_to

       Title: up_to
        Args: nodename str
      Return: node stag
     Example: $stag->up_to('blah');