XML::SAX::Base - phpMan

NAME
    XML::SAX::Base - Base class SAX Drivers and Filters

SYNOPSIS
      package MyFilter;
      use XML::SAX::Base;
      @ISA = ('XML::SAX::Base');

DESCRIPTION
    This module has a very simple task - to be a base class for PerlSAX
    drivers and filters. It's default behaviour is to pass the input
    directly to the output unchanged. It can be useful to use this module as
    a base class so you don't have to, for example, implement the
    characters() callback.

    The main advantages that it provides are easy dispatching of events the
    right way (ie it takes care for you of checking that the handler has
    implemented that method, or has defined an AUTOLOAD), and the guarantee
    that filters will pass along events that they aren't implementing to
    handlers downstream that might nevertheless be interested in them.

WRITING SAX DRIVERS AND FILTERS
    The Perl Sax API Reference is at
    <http://perl-xml.sourceforge.net/perl-sax/>.

    Writing SAX Filters is tremendously easy: all you need to do is inherit
    from this module, and define the events you want to handle. A more
    detailed explanation can be found at
    http://www.xml.com/pub/a/2001/10/10/sax-filters.html.

    Writing Drivers is equally simple. The one thing you need to pay
    attention to is NOT to call events yourself (this applies to Filters as
    well). For instance:

      package MyFilter;
      use base qw(XML::SAX::Base);

      sub start_element {
        my $self = shift;
        my $data = shift;
        # do something
        $self->{Handler}->start_element($data); # BAD
      }

    The above example works well as precisely that: an example. But it has
    several faults: 1) it doesn't test to see whether the handler defines
    start_element. Perhaps it doesn't want to see that event, in which case
    you shouldn't throw it (otherwise it'll die). 2) it doesn't check
    ContentHandler and then Handler (ie it doesn't look to see that the user
    hasn't requested events on a specific handler, and if not on the default
    one), 3) if it did check all that, not only would the code be cumbersome
    (see this module's source to get an idea) but it would also probably
    have to check for a DocumentHandler (in case this were SAX1) and for
    AUTOLOADs potentially defined in all these packages. As you can tell,
    that would be fairly painful. Instead of going through that, simply
    remember to use code similar to the following instead:

      package MyFilter;
      use base qw(XML::SAX::Base);

      sub start_element {
        my $self = shift;
        my $data = shift;
        # do something to filter
        $self->SUPER::start_element($data); # GOOD (and easy) !
      }

    This way, once you've done your job you hand the ball back to
    XML::SAX::Base and it takes care of all those problems for you!

    Note that the above example doesn't apply to filters only, drivers will
    benefit from the exact same feature.

METHODS
    A number of methods are defined within this class for the purpose of
    inheritance. Some probably don't need to be overridden (eg parse_file)
    but some clearly should be (eg parse). Options for these methods are
    described in the PerlSAX2 specification available from
    http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/~checkout~/perl-xml/libxm
    l-perl/doc/sax-2.0.html?rev=HEAD&content-type=text/html.

    *   parse

        The parse method is the main entry point to parsing documents.
        Internally the parse method will detect what type of "thing" you are
        parsing, and call the appropriate method in your implementation
        class. Here is the mapping table of what is in the Source options
        (see the Perl SAX 2.0 specification for the meaning of these
        values):

          Source Contains           parse() calls
          ===============           =============
          CharacterStream (*)       _parse_characterstream($stream, $options)
          ByteStream                _parse_bytestream($stream, $options)
          String                    _parse_string($string, $options)
          SystemId                  _parse_systemid($string, $options)

        However note that these methods may not be sensible if your driver
        class is not for parsing XML. An example might be a DBI driver that
        generates XML/SAX from a database table. If that is the case, you
        likely want to write your own parse() method.

        Also note that the Source may contain both a PublicId entry, and an
        Encoding entry. To get at these, examine $options->{Source} as
        passed to your method.

        (*) A CharacterStream is a filehandle that does not need any
        encoding translation done on it. This is implemented as a regular
        filehandle and only works under Perl 5.7.2 or higher using PerlIO.
        To get a single character, or number of characters from it, use the
        perl core read() function. To get a single byte from it (or number
        of bytes), you can use sysread(). The encoding of the stream should
        be in the Encoding entry for the Source.

    *   parse_file, parse_uri, parse_string

        These are all convenience variations on parse(), and in fact simply
        set up the options before calling it. You probably don't need to
        override these.

    *   get_options

        This is a convenience method to get options in SAX2 style, or more
        generically either as hashes or as hashrefs (it returns a hashref).
        You will probably want to use this method in your own
        implementations of parse() and of new().

    *   get_feature, set_feature

        These simply get and set features, and throw the appropriate
        exceptions defined in the specification if need be.

        If your subclass defines features not defined in this one, then you
        should override these methods in such a way that they check for your
        features first, and then call the base class's methods for features
        not defined by your class. An example would be:

          sub get_feature {
              my $self = shift;
              my $feat = shift;
              if (exists $MY_FEATURES{$feat}) {
                  # handle the feature in various ways
              }
              else {
                  return $self->SUPER::get_feature($feat);
              }
          }

        Currently this part is unimplemented.

    *   set_handler

        This method takes a handler type (Handler, ContentHandler, etc.) and
        a handler object as arguments, and changes the current handler for
        that handler type, while taking care of resetting the internal state
        that needs to be reset. This allows one to change a handler during
        parse without running into problems (changing it on the parser
        object directly will most likely cause trouble).

    *   set_document_handler, set_content_handler, set_dtd_handler,
        set_lexical_handler, set_decl_handler, set_error_handler,
        set_entity_resolver

        These are just simple wrappers around the former method, and take a
        handler object as their argument. Internally they simply call
        set_handler with the correct arguments.

    *   get_handler

        The inverse of set_handler, this method takes a an optional string
        containing a handler type (DTDHandler, ContentHandler, etc.
        'Handler' is used if no type is passed). It returns a reference to
        the object that implements that class, or undef if that handler type
        is not set for the current driver/filter.

    *   get_document_handler, get_content_handler, get_dtd_handler,
        get_lexical_handler, get_decl_handler, get_error_handler,
        get_entity_resolver

        These are just simple wrappers around the get_handler() method, and
        take no arguments. Internally they simply call get_handler with the
        correct handler type name.

    It would be rather useless to describe all the methods that this module
    implements here. They are all the methods supported in SAX1 and SAX2. In
    case your memory is a little short, here is a list. The apparent
    duplicates are there so that both versions of SAX can be supported.

    *   start_document

    *   end_document

    *   start_element

    *   start_document

    *   end_document

    *   start_element

    *   end_element

    *   characters

    *   processing_instruction

    *   ignorable_whitespace

    *   set_document_locator

    *   start_prefix_mapping

    *   end_prefix_mapping

    *   skipped_entity

    *   start_cdata

    *   end_cdata

    *   comment

    *   entity_reference

    *   notation_decl

    *   unparsed_entity_decl

    *   element_decl

    *   attlist_decl

    *   doctype_decl

    *   xml_decl

    *   entity_decl

    *   attribute_decl

    *   internal_entity_decl

    *   external_entity_decl

    *   resolve_entity

    *   start_dtd

    *   end_dtd

    *   start_entity

    *   end_entity

    *   warning

    *   error

    *   fatal_error

TODO
      - more tests
      - conform to the "SAX Filters" and "Java and DOM compatibility"
        sections of the SAX2 document.

AUTHOR
    Kip Hampton (khampton AT totalcinema.com) did most of the work, after
    porting it from XML::Filter::Base.

    Robin Berjon (robin AT knowscape.com) pitched in with patches to make it
    usable as a base for drivers as well as filters, along with other
    patches.

    Matt Sergeant (matt AT sergeant.org) wrote the original XML::Filter::Base,
    and patched a few things here and there, and imported it into the
    XML::SAX distribution.

SEE ALSO
    XML::SAX