Evangelo Prodromou > JOAP-0.01 > JOAP::Proxy::Class



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JOAP::Proxy::Class - Base class for client-side proxies of JOAP classes


  package FooProxy;
  use JOAP::Proxy::Package::Class;
  use base qw(JOAP::Proxy::Package::Class);

  FooProxy->Address('Foo@bar.example.com'); # say what class this is proxying for

  package main;

  # do Net::Jabber connection stuff here...

  $con = get_jabber_connection(); # You work this out


  # update class attributes with server values


  # get an attribute value with the automagic accessor

  my $height = FooProxy->height;

  # set an attribute with the automagic accessor

  FooProxy->height($height + 1);

  # save class attributes to server


  # call a class method, with automagic method thingy


  # get a proxy to a remote instance

  my $foo1 = FooProxy->get('Foo@bar.example.com/Number1');

  # refresh instance with attribute values from server


  # read an instance attribute using the Magic Accessor

  my $name = $foo1->name;

  # set an instance attribute (did I mention the magic accessors?)


  # save to the server


  # call an instance method

  $foo1->scratch_where_it_itches(1, 2, 3);

  # call a class method (not recommended) on an instance


  # read or write a class attribute using an accessor on an instance

  my $height2 = $foo->height;
  $foo->height($height + 17);

  # create a new instance

  my $foo2 = FooProxy->add(name => 'gar', drink => 'beaujolais');

  # search for instances matching criteria

  my @matches = FooProxy->search(name => 'troyd');

  # delete an instance



This is an abstract superclass for proxies to JOAP classes. Its intent is to make it easy -- nay, trivial -- to build and use proxy classes.


JOAP servers support three kinds of objects: servers, classes, and instances. Ignoring servers for a moment, the most natural map of this into Perl is to have JOAP classes be Perl classes, and JOAP instances be instances of the corresponding Perl class.

That's the model that this module supports. You can normally just treat the proxy class as if it were the remote class, and the proxy instance as if it were the remote instance.

The mainline usage of this module is to create a new Perl class that is a subclass of JOAP::Proxy::Package::Class, define its address, and then use it right away. The JOAP::Proxy classes will figure out what the right accessors, mutators, and methods should be automagically.

You can, if you want to avoid the automagic-figure-stuff-out step, also define the attributes, methods, and other metadata of a class. This can be error-prone, however, since typos and stuff will keep your class from working correctly, in weird ways. It's probably is not worth the effort of saving one round-trip to the object server per program invocation if done by hand. There is a tool to do it automatically, though. See joappxgen, the JOAP proxy code generator, for details.

As a word of warning, this package is still in early experimental stage. You're going to have enough gotchas with the recommended interface, so don't give yourself more trouble by doing things I don't recommend.

Most of the interface is inherited from various superclasses, but I document it here for convenience. For terminology, I try to use 'remote method' for JOAP methods of the remote class or instance, and 'local method' for methods of the local Perl package or instance, when I think the meaning is unclear.

One last thing: it's essential to set the Connection class attribute of the JOAP::Proxy class before using any of the methods in this package (except maybe Address). See JOAP::Proxy for more information.

Class Methods

There are a number of class methods for different use; I separate them here for sanity's sake.

Data Manipulation Methods

These are methods that you're going to use over and over. In general, they should be called on the class itself, rather than on instances. Some have different behavior if called on instances (see below), and some will throw an error if called on instances.


Returns a proxy version of the instance at $inst_address as an instance of this class. The instance attributes will be populated with its current values.

See JOAP::Addresses for more information on properly-formatted addresses. If you only know some attributes of the instance, you should use the "search" method described below.

add(attr1 => $value1, attr2 => $value2, ...)

Adds a new instance (remotely) and returns a proxy version as an instance of this class. All required, writable attributes of the class must be present for it to work. You can include other instance attributes, also, but they must be writable.

This will throw an error if called on an instance.

search(attr1 => $spec1, attr2 => $spec2, ...)

Returns a list of all remote instances that match all the search specifications. The specifications are logically ANDed -- only instances that match all specification values will be returned. An example:

    my @rectangles = Shape->search(sides => 4, angle => 90.0);

    foreach my $address (@rectangles) {
        my $rect = Shape->get($address);

The semantics of the spec values is somewhat complicated -- see the JOAP specification for full details. In general, numeric and date types are matched exactly, while string types are matched if the spec value is a substring of the instance value.

Class attributes cannot be used as arguments to search().

As a special case, search() with no arguments returns a list of all instances.

This method will throw an error if called on an instance.


As a class method, reads the remote class attributes and caches them. If the metadata has not already been read, will also get that stuff, too.

In general, calling this method on the class before doing anything else is a good idea.

Calling this method on an instance has different behavior; see below.


Saves the cached values of the class attributes to the remote server.

Calling this method on an instance has different behavior; see below.

Introspection Methods

These methods return information about the structure of the class. It's generally a bad idea to use them as mutators (with arguments), unless you really really know what you're doing.


The address of the remote class this class is a proxy for. This is the only introspection method application code should use as a mutator. It's mostly useful when several object servers at different locations use the same interface; you can say which one you're interested in by changing this classes address.


Returns a reference to a hashtable mapping attribute names to attribute descriptors. See JOAP::Descriptors for more information on these data structures.


Returns a reference to a hashtable mapping method names to method descriptors. See JOAP::Descriptors for more information on these data structures.


The date and time that the class structure description was downloaded from the remote class. It's in ISO 8601 format; see JOAP::Types for details.

Note that this is also used internally as a flag to indicate that the class structure has been downloaded at all. If you set this attribute, without setting all the other instrospection attributes, bad things will most definitely occur.


A human-readable general description of the purpose and behavior of the class.


A reference to a list of addresses of remote classes that are superclasses of this class. This implies no local hierarchy of classes; it's only here to make typing decisions. It's currently not used in the internals of the proxy code.

Code-Generation Methods

These methods are of use really only for code generators. Don't use them to call methods or accessors; use the autoloading interface instead.


Return a closure that would work well as a class accessor for attribute $name. You can install it in a package like this:

    *some_attribute = Package->class_accessor('some_attribute');

Return a closure that would work well as a class method for method $name.


Return a closure that would work well as an instance accessor for attribute $name.


Return a closure that would work well as an instance method for method $name.

Instance Methods

The following methods are for use on instances. Some of them will throw errors when called on a class; others have different behavior when called on a class.

Data Manipulation Methods


Read the attributes of this remote instance and store them locally in the proxy instance. The attributes can then be queried using the accessors.

Note that the behavior of this method is different when called on a class.


Save the local values of attributes to the remote instance. This will only save writable, instance attributes.

Some classes have instance addresses that are calculate from their attribute values; you should not count on an instance address being the same after a save(). Of course, the Perl reference will be the same.

If the instance has read-only attributes, it's a good idea to call refresh() after each save to ensure that all attributes are sync'd.

Note that the behavior of this method is different when called on a class.


Delete the remote instance. The local proxy will still have all its attributes, so you can query them, but it will no longer be "linked" to the remote instance. Calling remote methods, or any of the data manipulation methods, will most likely result in an error.

Introspection Methods

You can call any of the class introspection methods on an instance, but it looks funny and is not recommended. The following is really the only introspection method that makes sense:


The address of the remote instance. This value is set when the object is constructed using get or add; it can sometimes be changed by save.

See JOAP::Addresses for more details on the format of JOAP addresses.

Autoloaded Methods

One of the key bennies to this package is that you can just go blithely around using accessors, mutators, and remote methods of the remote class or instance without really having to write any code for them.

For attributes, an eponymous ("same named") accessor will be created that will return the value of the attribute.

    my $gar = $foo->gar;

If the attribute is writable, the same local method can be used as a mutator by passing a single value as the argument to the method.

    $foo->gar('gar gar gar!');

If the attribute is also a class attribute, it can be called on the class:

    my $height = FooProxy->height;

Calling an accessor for an instance attribute on a class will cause a runtime error. So don't do that.

For remote methods, an eponymous local method is created that takes the same arguments and has the same return type as the remote method. This works for both class and instance methods.


    my $new_value = $foo->increment_counter;

A runtime error will be thrown if you call an instance method on a class.

Note that if there are remote methods or attributes that have the same name as one of the above built-in methods, they won't work. Similarly, if a remote method and a remote attribute have the same name, the remote method will be used.

There are also some internal methods that may cause interference with remote methods and attributes.


None by default.


The name of this package is real long.

There's a conceptual disconnect between mutators and methods. For performance reasons, mutators keep the values set in the local proxy until a save() call. But methods are called immediately. So, the following code will probably not do what you expect:

    # set an attribute using a mutator
    # call a method that changes that attribute as a side-effect
    my $result = $object->increment_counter;

The increment_counter method will use the value on the server, not the local cached value of 42, of counter. You need to do this:

    # set an attribute using a mutator
    # save it
    # call a method that changes that attribute as a side-effect
    my $result = $object->increment_counter;

Future versions may call save() before executing a method if the local proxy has been changed and not yet saved.

You can use mutators on instances for class attributes, but you have to call the class save() method to save them.

Mapping a single subclass of this class to two different servers is asking for trouble.

The thread-safety attributes aren't specified for methods defined in this package nor for autoloaded methods.

There's currently no workaround for name clashes between attributes and methods and between local built-in methods and either of these.

There are probly lots more bugs lurking silently.


You should see JOAP::Proxy to figure out how to make your initial Jabber connection.

JOAP::Types has more info on JOAP data types.

JOAP::Descriptors has more info on the structure of attribute and method descriptors. JOAP::Addresses has some clues about the structure of JOAP addresses.

joappxgen, the JOAP proxy generator, can be used to pre-cook subclasses of this class for a small bump in performance.

There's more information in the JOAP documentation about how to contact the author of this package.


Evan Prodromou <evan@prodromou.san-francisco.ca.us>


Copyright (c) 2003, Evan Prodromou <evan@prodromou.san-francisco.ca.us>

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

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