OSGi, Scripting, RESTWebapps with Apache Sling

Carsten Ziegeler | Day Management AG

cziegeler@apache.org

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About• Member of the ASF– Sling, Felix, Cocoon, Portals, Sanselan,

Excalibur, Incubator– PMC: Felix, Portals, Sling, Incubator,

Excalibur (Chair)• RnD Team at Day Software• Article/Book Author, Technical

Reviewer• JSR 286 Spec Group (Portlet API 2.0)

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Agenda – Apache Sling1 Motivation2 Content and JCR3 Web and REST4 Scripting5 OSGi6 Outlook

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1 Motivation1 Motivation

Apache Sling

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• Publish huge amount of information– Different types– Highly dynamic– Different output formats

• Web 2.0 ready– Collaboration and integration

• Fast changing requirements– Rapid prototyping and development– Dynamic, extensible but maintainable

Web Challenges

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• Publish huge amount of information– Different types– Highly dynamic– Different output formats

• Web 2.0 ready– Collaboration and integration

• Fast changing requirements– Rapid prototyping and development– Dynamic, extensible but maintainable

Web Challenges

JCR

RESTROA

OSGi

Scripting

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• Web framework• Java content repository (JCR)• ROA / REST• Scripting inside• OSGi• Apache Open Source top level project

– http://sling.apache.org• Driving force behind several OSGi

related projects at Apache

5th Winner JAX Innovation Award 2008

Apache Sling – The Fun Is Back

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Apache Sling Powered Site

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2 Content/JCR2 Content/JCR

Apache Sling

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Content Is Important• Apache Sling makes handling content

easy• Java content repository (JCR)

– Several different sources possible• Direct mapping: URL -> content

– Configurable– http://myserver.domain/products/sling

.html• Flexible rendering

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Content Repository I• Features of an RDBMS

– Structure, integrity– Query, transactions

• Features of a filesystem– Hierarchy, binaries– Locking, access control

• All the other good stuff– Observation, versioning– Unstructured– Multi values, sort order, full text

• Single repository for all content!

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JCR – JSR 170, JSR 283• Content Repository for Java

technology API• (Java) Standard– Supported by many vendors– Used by many products and projects– Several open source solutions

• How do you connect to a CR?• How do you interact with a CR?

JSR 283 – Version 2.0 – Final since September 09

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Sample Application: Slingshot• Digital Asset Management– Hierarchical storage of pictures– Upload– Tagging– Searching– Automatic thumbnail generation

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Poor man's flickr...

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Slingshot Content Structure

Basel

City

Europe

Travel Family

Amsterdam

2007

Weddings

2008

Photo

Photo

Photo

Photo

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Content Repository II• Hierarchical content– Nodes and properties

• Structured– Nodetypes and typed properties

• And/or unstructured• Fine and coarse-grained• Single repository for all content!

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The Repository Model• Repository: one (or more) workspaces• Workspace contains a tree of items• Item: Node or property• Nodes provide the content structure– May have children

• Actual data is stored as values of properties

• Types and namespaces!

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Root

„Once upon a time..“

Nodes and Properties

Implementation of JCR

Basel

City

Europe

Travel Family

Amsterdam

2007

Weddings

2008

Photo

Photo

Photo

Photo

“Images from Europe“

Properties

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Apache Jackrabbit• JSR 170, JSR 283 reference

implementation• Apache TLP since 2006• Several releases• JCR 2.0 implementation end of 2009• Additional components

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Leverage the standard node types

• Type hierarchy • Content hierarchy

nt:hierarchyNode

nt:folder

nt:file

nt:linkedFile

nt:unstructured

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Bottom-up modeling: Node types

slingshot:photo > nt:file- slingshot:description (string)- slingshot:location (string)- slingshot:tags (string[])

slingshot:album > nt:folder- slingshot:description (string)- slingshot:date (date)

slingshot:tag- slingshot:description (string)

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Top-down modeling: Hierarchy

Basel

City

Europe

Travel Family

Amsterdam

2007

Weddings

2008

Photo

Photo

Photo

Photo

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3 ROA and REST3 ROA and REST

Apache Sling

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Resource Oriented Architecutre• Piece of information is a resource

– News entry, product, photo...– (Descriptive) URI

• Stateless– Request contains all relevant

information• Use HTTP

– Methods (GET, POST) for operations

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REST with Apache Sling• Default behaviour for GET• Creating/Updating content through

POST– Default behaviour

• Additional operations/method• Resource-first request processing!

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Resource• Sling's abstraction of the thing

addressed by the request URI– Usually mapped to a JCR node– File system, database...

• Properties of resources– Path, e.g. JCR Item path– Type, e.g. JCR node type– Metadata, e.g. last modification date

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• URI Decomposition– Resource and representation

•

• Content retrieved from repository• Rendering based on content type

Resource-first Request Processing

/slingshout/albums/travel.print.a4.html

Resource Path Selectors Extension

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Basic Request Processing Steps• URI decomposition• Resolve the resource (using URI)• Resolve rendering script– Source: resource type– Scripts wrapped by generic servlet

• Create rendering chain– Configurable (servlet) filters– Rendering servlet

• Invoke rendering chain

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Resource Resolver I• Tasks:– Finding Resources– Getting Resources– Simplification of Query Execution

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Resource Resolver II• Gateway for resources• Abstracts the path resolution• Abstracts access to the persistence

layer(s)• Configurable

– Mappings (Multi-site mgmt, beautify paths)

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Resource-First Request Processing

Resource Resolver

Script Resolver

Script

request

response

Resource (resource type)

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4 Scripting4 Scripting

Apache Sling

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Scripting Inside• It's your choice– JSP, servlet, ESP, Scala– javax.script (Apache BSF)– own script handlers

• Scripts stored in OSGi bundles or repository• Scripts are searched at configurable locatiosn• Default servlets (or scripts)

– JSON, XML– Registerable– Fallback / Last Ressort

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Script Resolving I• Path to script is built from ...– Configured search paths ( /apps, /libs )– Resource type converted to path

( slingshot/Album )– Selector string ( print/a4)– Request method & extension• GET --> Request URL Extension ( html )• else --> Method Name ( POST, PUT, ... )

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Script Resolving Example• URI:

/slingshot/albums/travel.print.a4.html• Resource: /slingshot/albums/travel• Resource Type: slingshot:Album• Script for GET:– /apps/slingshot/Album/print/a4/html.*

• Script for POST:– /libs/slingshot/Album/print/a4/POST.*

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Script Resolving II• Scripts are searched by best matching

– /apps/slingshot/Album/print/a4/html.*– /libs/slingshot/Album/print/a4/html.*– /apps/slingshot/Album/html.*– /libs/slingshot/Album/html.*

• Resource has a type and a super type– Script inheritance– Default script (JSON...)

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Powerful Scripting with Includes I

Resource Resolver

Script Resolver

Script

Request: /slingshot/albums/travel.html

response

Resource, resource type: slingshot:Album

Script: /libs/slingshot/Album/html.jsp

Generates main htmlsling:include with selectors

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Script (/libs/slingshot/Album/html.jsp)

Powerful Scripting with Includes II

<sling:include resource="<%= current %>" addSelectors="main"/>…

Script Resolver

Request: /slingshot/albums/travel.html

response

Script

Script: /libs/slingshot/Photo/tree.html.jsp

for(current : ChildResources)

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• ROA• URI decomposition• Resource resolving• Script resolving

– Recursion• Flexible script search algorithm

Resource-first Request Processing

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5 OSGi5 OSGi

Apache Sling

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Runtime Framework: Requirements• Modularization – Modularity is key

– Manage growing complexity– Support (dynamic) extensibility

• Lifecycle management• Configuration management• Dependency management– Modules, services– Different distributions

• Dynamic System Changes

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OSGi in 5..ehm..1 Minute

• Specification of a framework• Module concept (bundles) with lifecycle• Simple but powerful component model

– Lifecycle management– Publish/Find/Bind service registration

• Dynamic!• Uses the concept of bundles

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An OSGi Bundle• Leverages the Java packaging

mechanism: JAR files• Contains Java classes and resources• Additional meta-data– Implicit dependencies to other bundles– Package imports/exports

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Services• OSGi offers an API to register services– Service is registered by its interface

name(s)– Implementation is bundle private– Several components for same service

possible (from different bundles)• Bundles can query services– By interface names– With additional filters

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The OSGi Core• Minimal but sufficient API for services– Minimal overhead: Good for simple

bundles– No support for component management– No support for configuration management– Requires sometimes a lot of Java coding

• Additional (optional) OSGi extensions– Declarative Service Specification – Configuration Admin Service Specification

Dynamic Services• OSGi Declarative Services Spec– XML Configuration (in a bundle)– Publishing services– Consuming services• Policy (static,dynamic), cardinality (0..1, 1..1,

0..n)– Default configuration– Service Lifecycle management

• Various Implementations– Apache Felix SCR

Config Admin and Metatype• OSGi Config Admin– Configuration Manager– Persistence storage– API to retrieve/update/remove configs– Works with Declarative Services

• OSGi Metatype Service– Description of bundle metadata– Description of service configurations

• Various Implementations– Apache Felix (Reference Implementation)

Apache Felix• Top-level project (March 2007)• Healthy and diverse community• OSGi R4 (R4.2) implementation– Framework (frequent releases)– Services (continued development)

• Tools– Maven Plugins, Web Console, iPojo

• New sub project– Karaf : Runtime Environment (OSGi Kernel)– Sigil: OSGi tooling

Contributions to Apache Felix• Declarative service• Config admin• Metatype service• Preferences service• Web console (!)• Maven SCR Plugin (!)

Apache Sling Runtime• Uses Apache Felix• Runtime: Apache Sling Launchpad

– Might be merged with Felix Karaf• Two flavours

– Standalone Java Application– Web application

• But Sling can be deployed in any OSGi framework!

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Standalone Java Application• One single executable JAR file• Small Launcher• Starts OSGi Framework (Apache

Felix)• Uses Jetty in an OSGi Bundle

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Web Application• Extends Standalone Application– Replaces Main with a Servlet

• Uses a bridge to connect Sling to the Servlet Container

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Facts about Sling• Sling API– No reference to JCR API– Uses resource abstraction

• 36 maintained bundles (many optional)– Over 25 additional bundles

• Highly modular and runtime configurable– OSGi framework– Everything is a OSGi bundle

• ConfigAdmin, Declarative Services, Metatype• Felix Web Console

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6 Outlook6 Outlook

Apache Sling

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Current State• Apache Sling is a top level project• New convenience Release

– Frequent releases of various bundles• Demo Applications• Increasing interest -> Increasing

community

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Development• Easy to get started

– Add content, add script, add more content

• Very flexible and dynamic• Tooling– Maven Plugins– Apache Felix SCR Plugin– Additional Sling Plugins– But not tied to Maven of course :)

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And remember...• (Nearly) Everything is content– Application content– HTML pages, CSS and JavaScript files,

static images– Documentation, resource bundles, etc.– With versioning, export/import, full text

search, etc.

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• Publish huge amount of information– Different types– Highly dynamic– Different output formats

• Web 2.0 ready– Collaboration and integration

• Fast changing requirements– Rapid prototyping and development– Dynamic, extensible but maintainable

Manage the Web Challenges...

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with Apache Sling: State of the Art• Modularity and dynamics (OSGi)• Content Management (JCR)• Resource oriented architecture

(REST)• Scripting inside

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Apache Sling – The Fun is Back!• Web Framework• Java Content Repository• REST• Scripting inside• OSGi• Apache Open Source project• Check it out today!

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Thanks for your attention!

Q&A

Apache Sling