The document discusses Java Content Repository (JCR) and Sling, describing them as standards and frameworks that provide content-centric interfaces and services for content management applications. JCR defines a content model and Java API for storing and managing diverse content. Sling is a scriptable application layer built on JCR that processes HTTP requests in a RESTful manner and allows developing applications using OSGi bundles and scripting languages. It also provides examples of using Sling with CURL to create and retrieve content from a repository.

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JCR & Sling quick dive
Paolo Mottadelli | Senior Sales Engineer

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Background
■ The 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 identifiers
■ Standard methods
■ Extensible representation types
■ Simplified 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
■ The 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
■ The JCR specification defines 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: The Repository Model
■ Workspaces
■ Hierarchy of nodes
■ Properties associated to a node
■ Node types define 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 notification 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. file storage)
■ Needs definition 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:lastModified
primaryitem jcr:data
- jcr:data (BINARY) mandatory

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JCR: node types & mixin types
■ predefined node types:
■ nt:unstructured
■ nt:file
■ nt:folder
■ nt:resource represents the actual content of a file.
■ 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 (http://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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The 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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OSGIframework (felix)
JCRrepository (jackrabbit)
JCR api
Applicationframework (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
jackrabbit
JCR api
HTTP
standard
servlets
custom servlets
and components
resource
resolution
servlet/script
resolution
JSR 223
scripting
javascript
Ruby
WedDAV
server
sling OSGI
console
sling
JSP
Scala
...

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Sling examples using cURL
■ Create a node
■ curl -F"sling:resourceType=foo/bar" -F"title=some title" http://admin:admin@localhost:7402/content/mynode
■ Create a node (auto-named)
■ curl -X POST "http://admin:admin@localhost:7402/content/blog"
■ curl -D - -F"title=Adventures with Sling" "http://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
defines the resource defines the rendition

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Sling URL decomposition
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/geometrixx/en/products/triangle.teaser.html
sling:resourceType
geometrixx/components/contentpage

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Where to go from here
■ JSR 283 spec: http://jcp.org/en/jsr/detail?id=283
■ Apache Jackrabbit: http://jackrabbit.apache.org/
■ Apache Sling: http://sling.apache.org/
■ First steps with CRX:
■ http://dev.day.com/docs/en/crx/current/getting_started/first_steps_with_crx.html
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