MOD_PERL_METHODUserDContributed Perl DMOD_PERL_METHOD_HANDLERS(1)NAMEmod_perl_method_handlers - How to use mod_perl's Method
Handlers
DESCRIPTION
Described here are a few examples and hints how to use
MethodHandlers with modperl.
This document assumes familiarity with at least the perl
toot manpage 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 ($$) {
my($class, $r) = @_;
...;
}
__END__
Configuration:
PerlHandler My
or
PerlHandler My->handler
Since the handler is invoked as a method, it may inherit
from other classes:
PerlHandler My->method
In this case, the 'My' class inherits this method from
'BaseClass'.
In Perl 5.6.0 or later, you can use subroutine attributes
in place of subroutine prototypes:
package My;
@ISA = qw(BaseClass);
sub handler : method {
my($class, $r) = @_;
...;
}
see the the attributes manpage manpage for additional
information on subroutine attributes.
To build in the ability to specify Perl*Handlers as method
handlers, configure mod_perl with:
% perl Makefile.PL PERL_METHOD_HANDLERS=1 [PERL_FOO_HOOK=1,etc]
WHY?
The short version: For pretty much the same reasons we're
using OO perl everywhere else. :-) See the perltoot man
page.
The slightly longer version would include some about code
reusage and more clean interface between modules.
SIMPLE EXAMPLE
Let's start with a simple example.
In httpd.conf:
<Location /obj-handler>
SetHandler perl-script
PerlHandler $My::Obj->method
</Location>
In startup.pl or another PerlRequire'd file:
package This::Class;
$My::Obj = bless {};
sub method ($$) {
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::Arti
cle 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 some
thing 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 subrou
tine 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 pub
lic release.
Some codesnippets is from Doug MacEachern.
SEE ALSO
the mod_perl manpage, the Apache manpage, the perltoot
manpage (also available at
"http://www.perl.com/CPAN/doc/FMTEYEWTK/perltoot.html")
2002-03-23 mod_perl-1.2MOD_PERL_METHOD_HANDLERS(1)
