Alfresco 3 Thumbnails and the Forge Project

The thumbnails forge project was started quite a while ago (like Alfresco 0.9 or so… old school) and the first public release was put on the forge in late 2006 (which would have been around Alfresco 1.3 I guess).

The project gained the attention of the Alfresco team and they contacted me about making a few changes to bring it more inline with what they had in mind for an implementation, notably creating a public thumbnail service. Those changes were made and I continued to collaborate with Alfresco on the forge project and gave input on their implementation.

Alfresco 3 now has a native implementation of thumbnails and version 1.0 of the forge project migrated to the new architecture, but it’s still cool.

Here’s a look at some of the differences to be aware of between the old thumbnails project implementation and Alfresco’s new native thumbnails:

Concept Pre 1.0 Versions of Forge Project Alfresco 3 Native

The service responsible for generating and retrieving thumbnails

ThumbnailService

The generateThumbnails method would create thumbnails for
all ThumbnailSpecifications defined.

A specific thumbnail can be generated with overriding options
(possibly defined by a user in the web interface) which
are merged with the defaults of the
ThumbnailSpecification
(useful in defining the offset for a video thumbnail for example).

ThumbnailService

The createThumbnail and updateThumbnail
methods are given the specific TransformationOptions to
use in generating the thumbnail.

The content property from which the source data will be read
must be specified when generating the thumbnail, the default cm:content
will not be assumed.

A common size and destination mimetype for thumbnails

ThumbnailSpecification

ContentTransformers and corresponging command line options explicitly
defined in config

ThumbnailDefinition

ContentTransformer determined by ContentService
from the given TransformationOptions

The detailed resizing specifications

TransformerSpecification

The specific ContentTransformer to use and the necessary
command line options are defined

TransformationOptions

The resizing details are specified using classes containing generic
definitions (for example ImageResizeOptions used by
the ImageTransformationOptions class) which are then
translated to appropriate command line code by the ContentTransformer
found by the ContentService

The model type

tn:thumbnail

<parent>cm:cmobject</parent>

Not being of type content prevents most rules from being run on
thumbnail nodes lest we do something unnecessary and resource intensive
like extract metadata or even create another thumbnail of a thumbnail node
and prevents thumbnail nodes from being indexed or returned in a search.

cm:thumbnail

<parent>cm:content</parent>

Care must be taken to not run rules or index thumbnail nodes since they
extend content.

One suggestion has been to add the following to the thumbnail type:

<aspect name="rule:ignoreInheritedRules">

<title>Ignore Inherited Rules</title>

</aspect>

The model property name of the common size and mimetype destination definition

tn:specificationName

The specifiationName was the name of the
ThumbnailSpecification used to generate the thumbnail.

cm:thumbnailName

The new CreateThumbnailActionExecuter uses the user-chosen
thumbnailName to retrieve the
ThumbnailDefinition but the relationship between the
ThumbnailDefinition and its thumbnailName is
not enforced by the ThumbnailService.

Default thumbnail sizes (max length/width)

`SMALL`	80px	JPEG
`MEDIUM`	160px	JPEG

`medium`	100px	JPEG
`doclib`	100px	PNG
`webpreview`	–	SWF
`imgpreview`	480px	PNG
`avatar`	64px	PNG

Strikethroughs represent deprecated items.
Avatar thumbnail size has nothing to do with what I can only assume is an incredibly overhyped movie about pissed off blue tree people since I haven’t been to a theater in like 10 years.

This information has been available in the thumbnails project’s 1.0 release readme but as it’s not shown by default I figured I’d post here as well.