mod_perl_method_handleUserpContributed Perl Documemodtperl_method_handlers(3p)



NAME
       mod_perl_method_handlers - How to use mod_perl's MethodHandlers

DESCRIPTION
       Described here are a few examples and hints how to use MethodHandlers
       with modperl.

       This document assumes familiarity with at least perltoot and "normal"
       usage of the Perl*Handlers.

       It isn't strictly modperl related, more like "what I use objects for in
       my modperl environment".

SYNOPSIS
       If a Perl*Handler is prototyped with '$$', this handler will be invoked
       as method, being passed a class name or blessed object as its first
       argument and the blessed request_rec as the second argument, e.g.

        package My;
        @ISA = qw(BaseClass);

        sub handler ($$) {
            my($class, $r) = @_;
            ...;
        }

        package BaseClass;

        sub method ($$) {
            my($class, $r) = @_;
            ...;
        }

        __END__

       Configuration:

        PerlHandler My

       or

        PerlHandler My->handler

       Since the handler is invoked as a method, it may inherit from other
       classes:

        PerlHandler My->method

       In this case, the 'My' class inherits this method from 'BaseClass'.

       In Perl 5.6.0 or later, you can use subroutine attributes in place of
       subroutine prototypes:

        package My;
        @ISA = qw(BaseClass);

        sub handler : method {
            my($class, $r) = @_;
            ...;
        }

       see the attributes manpage for additional information on subroutine
       attributes.

       To build in the ability to specify Perl*Handlers as method handlers,
       configure mod_perl with:

        % perl Makefile.PL PERL_METHOD_HANDLERS=1 [PERL_FOO_HOOK=1,etc]

WHY?
       The short version: For pretty much the same reasons we're using OO perl
       everywhere else. :-) See perltoot.

       The slightly longer version would include some about code reusage and
       more clean interface between modules.

SIMPLE EXAMPLE
       Let's start with a simple example.

       In httpd.conf:

        <Location /obj-handler>
        SetHandler perl-script
        PerlHandler $My::Obj->method
        </Location>

       In startup.pl or another PerlRequire'd file:

        package This::Class;

        $My::Obj = bless {};

        sub method ($$) {
            my($obj, $r) = @_;
            $r->send_http_header("text/plain");
            print "$obj isa ", ref($obj);
            0;
        }

       which displays:

        This::Class=HASH(0x8411edc) isa This::Class

A LITTLE MORE ADVANCED
       That wasn't really useful, so let's try something little more advanced.

       I've a little module which creates a graphical 'datebar' for a client.
       (See "http://www.hip.dk/date_bar"). It's reading a lot of small gifs
       with numbers and weekdays, and keeping them in memory in GD.pm's native
       format, ready to be copied together and served as gifs.

       Now I wanted to use it at another site too, but with a different look.
       Obviously something to do with a object. Hence I changed the module to
       a object, and can now do a

        $Client1::Datebar = new Datebar(
                -imagepath => '/home/client1/datebar/',
                -size      => [131,18],
                -elements  => 'wday mday mon year hour min',
        );

        $Client2::Datebar = new Datebar
                -imagepath => '/home/client2/datebar/',
                -size      => [90,14],
                -elements  => 'wday hour min',
        );

       And then use $Client1::Datebar and $Client2::Datebar as PerlHandlers in
       my Apache configuration. Remember to pass them in literal quotes ('')
       and not "" which will be interpolated!

       I've a webinterface system to our content-database. I've created
       objects to handle the administration of articles, banners, images and
       other content.  It's then very easy (a few lines of code) to enable
       certain modules for each client, depending on their needs.

       Another area where I use objects with great success in my modperl
       configurations is database abstraction.  All our clients using the
       webinterface to handle f.x. articles will use a simple module to handle
       everything related to the database.  Each client have

        $Client::Article = new WebAjour::Article(-host => 'www.client.com');

       in a module what will be run at server startup.

       I can then use some simple methods from the $Client::Article object in
       my embperl documents, like:

        [- $c = $Client::Article->GetCursor(-layout=>'Frontpage') -]
        [$ while($c->Fetch) $]
          <h2>[+ $c->f('header') +]</h2>
          [+ $c->f('textfield') +]
        [$ endwhile $]

       Very very useful!

TRAPS
       mod_perl expects object handlers to be in the form of a string, which
       it will thaw for you. That means that something like

        $r->push_handlers(PerlHandler => '$self->perl_handler_method');

       This doesn't work as you might expect, since Perl isn't able to see
       $self once it goes to PerlHandler.

       The best solution to this is to use an anonymous subroutine and pass it
       $r yourself, like this:

        $r->push_handlers(PerlHandler =>
            sub {
                my $r = shift;
                $self->perl_handler_method($r);
            }
        );

AUTHOR
       This document is written by Ask Bjoern Hansen <ask@netcetera.dk> or
       <ask@apache.org>.  Corrections and suggestions are most welcome. In
       particular would more examples be appreciated, most of my own code is
       way too integrated with our system, which isn't suitable for public
       release.

       Some codesnippets is from Doug MacEachern.

SEE ALSO
       mod_perl, Apache, perltoot (also available at
       "http://www.perl.com/CPAN/doc/FMTEYEWTK/perltoot.html")



perl v5.12.2                      2002-01-22      mod_perl_method_handlers(3p)
