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When getting in first touch with CQ5 and CRX, shipped by Day Software, now part of Adobe, the stakeholders need to understand the basic concept of the Open Architecture embraced by those systems.This is an easy to understand introduction to JCR and Sling architecture.
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JCR & Sling quick divePaolo Mo"adelli | Senior Sales Engineer
©2010 Adobe Systems Incorporated. All Rights Reserved. Adobe Con!dential.
Background
■ !e WWW design approach:■ Single, simple standardize interface■ Independent from storage/creation■ Trascends the complexity
■ Same design principles for application development:■ Commitment to standardization ■ Simple, generic, Content-Centric interface
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Content-centric vs Control-centric interfaces
■ Content-centric interfaces principles:■ Uniform identi!ers■ Standard methods■ Extensible representation types■ Simpli!ed application integration (much less interfaces)
■ Content Repository API = Uniform interface
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Content Repository
■ A Content Repository supports:■ Diverse data:
■ small & large, structured & unstructured, binary, metadata & relationships■ Services:
■ access control, locking, versioning, transactions, observation
■ "e Java Content Repository provides:■ Abstraction of data storage■ Generalized content services■ Separation of real storage from application interactions■ Standard API
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JCR
■ !e JCR speci"cation de"nes an abstract model and a Java API for data storage and related services commonly used by content-oriented applications.
■ Target: any application that must handle both unstructured digital assets and structured or semi-structured information.
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JCR: !e Repository Model
■ Workspaces■ Hierarchy of nodes■ Properties associated to a node■ Node types de"ne constraints(properties and child nodes)
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Repository
Workspace Workspace Workspace
[root] [root] [root]
jcr:title = ‘Hello World’jcr:lastModifiedBy = ‘admin’
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JSON representation of a node
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http://localhost:7402/content/firststeps.infinity.json
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JCR code sample
Repository repository = new TransientRepository(); Session session = repository.login(new SimpleCredentials("username", "password".toCharArray()));
// Store content Node hello = root.addNode("hello"); Node world = hello.addNode("world"); world.setProperty("message", "Hello, World!"); session.save();
// Retrieve content Node node = root.getNode("hello/world"); System.out.println(node.getPath()); System.out.println(node.getProperty("message").getString());
// Remove content root.getNode("hello").remove(); session.save();
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JCR: Repository Functionalities
■ Level 1■ Login■ Read Nodes & properties■ XML export■ XPath queries■ Node types discovery■ Namespaces remapping
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■ Level 2■ Write nodes & properties■ XML Import■ Assign a node types to nodes■ Change namespace registry
■ Optional■ Locking■ Transactions■ Versioning
■ SQL search■ Observation
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JCR: Observation
■ Observation enables an application to receive noti"cation of persistence changes in the workspace. Base for BPM.■ NODE_ADDED■ NODE_MOVED■ NODE_REMOVED■ PROPERTY_ADDED■ PROPERTY_REMOVED■ PROPERTY_CHANGED
■ Can be asynchronous or journaled
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JCR: Content Modelling
■ 2 use cases:
■ Structured content (e.g. !le storage)■ Needs de"nition of content models;■ Needs a stable structure;■ nt:resource
■ Unstructured content■ Any properties and child nodes allowed■ nt:unstructured
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[nt:resource] > mix:mimeType, mix:lastModifiedprimaryitem jcr:data- jcr:data (BINARY) mandatory
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JCR: node types & mixin types
■ prede"ned node types:■ nt:unstructured■ nt:"le■ nt:folder■ nt:resource represents the actual content of a "le.■ nt:version
■ mixin types provide extra characteristics to the node:■ mix:versionable: allows a node to support versioning■ mix:lockable: enables locking capabilities■ mix:referenceable: provides an auto-created jcr:uuid property
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JCR Ecosystem
■ Open Standard■ Java Community Process (h"p://jcp.org)
■ Sustainability■ Reference Implementation & TCK
■ Apache infrastructure■ license, workspace, information
■ Community■ open review, testing & collaboration
■ Open adoption
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Sling
■ OSGI-based scriptable application layer on top of JCR
■ REST based web framework■ Content-driven, using a JCR content repository■ Powered by OSGi■ Scripting inside, multiple languages (JSP, server-side javascript, Scala, etc.)■ Apache Open Source project
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!e Sling style
■ If you happen to hear this sentence:■ “Sling is not a web applications framework, it’s a web framework.”
■ It means:■ Sling is built in a way that embraces the web.■ Sling design is based on the principles of the WWW.■ Sling processes HTTP requests in a RESTful way.
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CRX Architecture
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OSGI framework (felix)
JCR repository (jackrabbit)
JCR api
Application framework (sling)
HTTP
‣ manages bundles as app components‣ provides system services to bundles
‣ stores the content
‣ processes HTTP requests in a RESTful way
specification implementation
architectural style
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Sling Architecture
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felix
jackrabbitJCR api
HTTP
standardservlets
custom servletsand components
resourceresolution
servlet/scriptresolution
JSR 223scripting
javascript
Ruby
WedDAVserver
sling OSGIconsole
sling
JSP
Scala
...
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Sling examples using cURL
■ Create a node■ curl -F"sling:resourceType=foo/bar" -F"title=some title" h"p://admin:admin@localhost:7402/content/mynode
■ Create a node (auto-named)■ curl -X POST "h"p://admin:admin@localhost:7402/content/blog"■ curl -D - -F"title=Adventures with Sling" "h"p://admin:admin@localhost:7402/content/blog/*"
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Sling URL decomposition
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/geometrixx/en/products/triangle.html
/geometrixx/en/products/triangle.teaser.html
de#nes the resource de#nes the rendition
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Sling URL decomposition
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/geometrixx/en/products/triangle.teaser.html
sling:resourceTypegeometrixx/components/contentpage
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Where to go from here
■ JSR 283 spec: h#p://jcp.org/en/jsr/detail?id=283■ Apache Jackrabbit: h#p://jackrabbit.apache.org/■ Apache Sling: h#p://sling.apache.org/
■ First steps with CRX:■ h#p://dev.day.com/docs/en/crx/current/ge#ing_started/"rst_steps_with_crx.html
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