Rendition Service

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Introduction

The DM Rendition Service was added in Alfresco 3.3. Its purpose is to provide support for rendering content nodes into other forms, known as renditions. The rendition nodes are derived from their source node and as such can be updated automatically when their source node's content (or other properties) are changed. Examples of renditions include

  • reformatted content (essentially a transformation from one MIME-type to another)
  • rescaled images (including thumbnails)
  • the output of a Freemarker or XSLT template.

Renditions can be performed synchronously or asynchronously and can be created at a specified location within the Alfresco repository. By default they are created as primary children of their source node but it is possible to have them created at other nodes specified explicitly or as templated paths.

Terminology

Rendering Engines are responsible for performing the transformation on a source node to create a rendition. Different Rendering Engines will perform different types of transformation. They can be registered with the Rendition Service using a unique name.

Rendering Engine Definitions provide a description of a given Rendering Engine. Each Rendering Engine Definition exposes parameter definitions for all the parameters which can be provided to the associated Rendering Engine. Each parameter definition describes the parameter name, type and whether or not it is mandatory.

Rendition Definitions encapsulate all the necessary information for rendering a given source node into a rendition. This includes the Rendering Engine which is used to perform the rendition and all the parameter values specified. Rendition Definitions have unique, qualified names and can be persisted within the repository.

Composite Rendition Definitions are a special type of Rendition Definition which allow the creation of renditions which require a sequence of two or more transformation steps. For example, a Composite Rendition Definition could be used to first reformat a PDF document into a PNG image and then resize the image to a small thumbnail. Composite Rendition Definitions specify an ordered list of other Rendition Definitions to be sequentially executed, with the output of the previous transformation feeding in as the source node for the next definition. All Composite Rendition Definitions specify the Composite Rendering Engine for their transformations.

Templated paths are...

3.3

Overview

In version 3.3 of Alfresco, the Rendition Service offers the following features:

  • Register a new Rendering Engine with the Rendition Service.
  • Obtain registered Rendering Engines from the Rendition Service as follows
    • a list of all Rendering Engines
    • a specific, named Rendering Engine
  • Register a Rendition Definition with the Rendition Service.
  • Edit a registered Rendition Definition.
  • Persist Rendition Definitions within the repository.
  • Obtain a list of all registered Rendition Definitions from the Rendition Service.
  • Obtain a specific, named Rendition Definition from the Rendition Service.
  • Optionally specify a templated path at which the generated Rendition will be placed.
  • Optionally specify whether renditions are generated synchronously or asynchronously.
  • Automatically update renditions when their source node is updated.
  • Upgrades will be available to migrate 3.2 thumbnail data to 3.3 renditions.

Design

The DM Rendition Service reuses the Alfresco ActionService in order to provide such things as parameterisation and synchronous & asynchronous execution.

Code

In Alfresco 3.3 the Rendition Service is exposed at a Java Foundation API level and as part of the Alfresco JavaScript API. The public API classes can be found in Repository/source/java in the package org.alfresco.service.cmr.rendition. The spring configuration can be found at Repository/config/alfresco/rendition-services-context.xml The implementation classes (including the Java classes that support the JavaScript API) can be found in the package org.alfresco.repo.rendition and its subpackages.

RenditionServiceClassOverview.png

Content Modelling

The Rendition Service content model is available at Repository/config/alfresco/model/renditionModel.xml.

RenditionModel.png

  • The rn:renditioned aspect is applied to a source node for which renditions have been created. This aspect defines the child-association rn:rendition which models the relation between the source node and its rendition node(s).
  • rn:rendition and its child aspects rn:hiddenRendition and rn:visibleRendition model the rendition nodes themselves.
    • rn:hiddenRendition is applied to a rendition node which has its source node as its primary parent.
    • rn:visibleRendition is applied to a rendition node which has its source node as a secondary parent, but is primarily located under another node.

Some parts of the thumbnail content model are retained in 3.3 but should be considered as legacy. They have been moved from the contentModel.xml into the new renditionModel.xml.

  • The cm:thumbnailed aspect now has rn:renditioned as its parent aspect.
  • The cm:thumbnail type remains in order to support backwards compatibility with the 3.2 Thumbnail Service.

Rendering Engines

Base rendering engine

Reformat rendering engine

Image rendering engine

FreeMarker rendering engine

XSLT rendering engine

HTML rendering engine

Composite rendering engine

Rendition Definitions

Usage Examples (Java)

Registering a new Rendering Engine

Rendering Engines are registered with the Rendition Service through Spring dependency injection. rendition-services-context.xml declares an abstract bean called baseRenderingAction which is the parent bean for all rendering engines. baseRenderingAction itself is a child bean of the ActionService's action-executer bean.

Alfresco 3.3 provides a number of concrete rendering engine beans e.g. reformat within the same spring context file. In order to register a new rendering engine, simply add new spring bean definitions in the normal way.

Retrieving registered Rendering Engine Definitions

// Rendering Engine Definitions can be retrieved
// 1. as a list of all registered engine definitions
List<RenderingEngineDefinition> engineDefs = renditionService.getRenderingEngineDefinitions();

// 2. by name
//    This name must be the same as the spring bean name used for the rendering engine.
String renderingEngineName = "myEngineName";
RenderingEngineDefinition engineDef = renditionService.getRenderingEngineDefinition(renderingEngineName);

Creating a Rendition Definition

// Names must be provided for the rendition definition and the rendering engine to use.
QName  renditionName       = QName.createQName(NamespaceService.CONTENT_MODEL_1_0_URI, "myRendDefn");
String renderingEngineName = ReformatRenderingEngine.NAME;

// Create the Rendition Definition object.
RenditionDefinition renditionDef = renditionService.createRenditionDefinition(renditionName, renderingEngineName);

// Set parameters on the rendition definition.
renditionDef.setParameterValue(AbstractRenderingEngine.PARAM_MIME_TYPE, MimetypeMap.MIMETYPE_PDF);

Storing a Rendition Definition

// Store the Rendition Definition using the QName
// of the Rendition Definition as a unique identifier.
renditionService.saveRenditionDefinition(renditionDef);

Retrieving a Rendition Definition

// Rendition Definitions can be retrieved:
// 1. As a list of all stored Rendition Definitions
List<RenditionDefinition> definitions = renditionService.loadRenditionDefinitions();

// 2. As a list of stored Rendition Definitions filtered by Rendering Engine name.
String renderingEngineName = "myEngineName";
List<RenditionDefinition> definitions = renditionService.loadRenditionDefinitions();

// 3. As a single Rendition Definition, uniquely identified by its QName.
QName renditionName = QName.createQName(NamespaceService.CONTENT_MODEL_1_0_URI, "myRendDefn");
RenditionDefinition renditionDef = renditionService.loadRenditionDefinition(renditionName);

Editing an existing Rendition Definition

// Retrieve the existing Rendition Definition
QName renditionName = QName.createQName(NamespaceService.CONTENT_MODEL_1_0_URI, "myRendDefn");
RenditionDefinition renditionDef = renditionService.loadRenditionDefinition(renditionName);

// Make changes.
renditionDef.setParameterValue(AbstractRenderingEngine.PARAM_MIME_TYPE, MimetypeMap.MIMETYPE_PDF);
renditionDef.setParameterValue(RenditionService.PARAM_ORPHAN_EXISTING_RENDITION, true);

// Persist the changes.
renditionService.saveRenditionDefinition(renditionDef);

Performing a simple rendition

// A rendition definition is required to perform any rendition.
// The rendition definition can be loaded from the repository or created as shown above.
NodeRef sourceNode = // obtained in the usual way e.g. from nodeService
ChildAssociationRef renditionAssoc = renditionService.render(sourceNode, renditionDef);

Performing a composite rendition

// First obtain a Composite Rendition Definition
// This can be loaded from the repository or created as shown here.
QName renditionName = QName.createQName(NamespaceService.CONTENT_MODEL_1_0_URI, "myRendDefn");
CompositeRenditionDefinition compositeDefinition  = 
   renditionService.createCompositeRenditionDefinition(renditionName);

// Now specify which other renditions are to be performed as part of the composite rendition.
RenditionDefinition reformatDefinition = renditionService.load(reformatRenditionName);
RenditionDefinition rescaleImageDefinition = renditionService.load(rescaleImageRenditionName);

compositeDefinition.addAction(reformatDefinition);
compositeDefinition.addAction(rescaleImageDefinition);

// Perform the composite rendition
NodeRef sourceNode = // obtained in the usual way e.g. from nodeService
ChildAssociationRef renditionAssoc = renditionService.render(sourceNode, compositeDefinition);

Retrieving renditions for a node

NodeRef sourceNode = // obtained in the usual way e.g. from nodeService

// 1. Get all renditions with the specified node as their source.
List<ChildAssociationRef> allRenditions = renditionService.getRenditions(sourceNode);

// 2. Get the rendition with the specified source node and the specified rendition definition name.
//    If there is no matching rendition, null is returned
QName renditionName = QName.createQName(NamespaceService.CONTENT_MODEL_1_0_URI, "myRenditionDef");
ChildAssociationRef rendition = renditionService.getRenditionByName(sourceNode, renditionName);

// 3. Get the renditions with the specified source node whose MIME types match a filter
//    This example returns renditions whose mimetype starts with "image".
List<ChildAssociationRef> imageRenditions = renditionService.getRenditions(sourceNode, "image");

Specifying a RenditionDefinition as asynchronous or synchronous

This behaviour is inherited from the ActionService - remember that RenditionDefinition extends Action. So we can create a Rendition Definition as shown above and set it to execute asynchronously

RenditionDefinition renditionDef = // created as shown above

renditionDef.setExecuteAsynchronously(true);

Usage Examples (JavaScript)

Creating a Rendition Definition, setting parameters and performing a rendition

var renditionDefName = "cm:adHocRenditionDef";
var renderingEngineName = "imageRenderingEngine";

var renditionDef = renditionService.createRenditionDefinition(renditionDefName, renderingEngineName);

// Set some parameters.
renditionDef.parameters["rendition-nodetype"] = "cm:content";
renditionDef.parameters["xsize"] = 99;

// Now execute this rendition definition
renditionDef.execute(testSourceNode);

Retrieving renditions for a node

// Get all renditions
var allRenditions = renditionService.getRenditions(testSourceNode);

// Get named renditions
var doclibRendition = renditionService.getRenditionByName(testSourceNode, "cm:doclib");

// Get renditions by mimetype. The String parameter here is used as a prefix to match against the node content's MIME type.
// So "image" matches "image*" which is all image MIME types.
var imageRenditions = renditionService.getRenditions(testSourceNode, "image");
var swfRenditions = renditionService.getRenditions(testSourceNode, "application/x-shockwave-flash");

Upgrade from Alfresco 3.2 to Alfresco 3.3

Upgrading to the Rendition Service

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