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Apache Sling - Bringing Back the Fun

Apache SlingTM is an innovative web framework that is intended to bring back the fun to web development.

Discussions about Sling happen on our mailing lists, see the Project Information page for more info.

Apache Sling in five bullets points

  • 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

Apache Sling in a hundred words

Apache Sling is a web framework that uses a Java Content Repository, such as Apache Jackrabbit, to store and manage content.

Sling applications use either scripts or Java servlets, selected based on simple name conventions, to process HTTP requests in a RESTful way.

The embedded Apache Felix OSGi framework and console provide a dynamic runtime environment, where code and content bundles can be loaded, unloaded and reconfigured at runtime.

As the first web framework dedicated to JSR-170 Java Content Repositories, Sling makes it very simple to implement simple applications, while providing an enterprise-level framework for more complex applications.

News

  • New Release: Apache Sling Servlet Resolver 2.2.2 (December 10th, 2012)
  • New Releases: Apache Sling Settings 1.2.2, Apache Sling Auth Core 1.1.0, Apache Sling Commons Logservice 1.0.2, Apache Sling Installer Core 3.4.2, Apache Sling Scripting JSP 2.0.26, Apache Sling Commons Compiler 2.1.0, Apache Sling JCR Compiler 2.1.0, Apache Sling I18n 2.2.4, Apache Sling JCR Classloader 3.1.10, Apache Sling JCR Webdav 2.1.2, Apache Sling JCR Davex 1.1.0 (November 30th, 2012)
  • New Releases: Apache Sling Maven Launchpad Plugin 2.2.0, Apache Sling Commons OSGi 2.2.0, Apache Sling Launchpad Installer 1.2.0, Apache Sling Rewriter 1.0.4, Apache Sling Settings 1.2.0 (November 19th, 2012)
  • New Releases: Apache Sling API 2.3.0, Apache Sling Bundle Resource Provider 2.1.0, Apache Sling File System Resource Provider 1.1.0, Apache Sling JCR Resource 2.2.0, Apache Sling Resource Resolver 1.0.0, Apache Sling Servlets Get 2.1.4, Apache Sling Servlets Post 2.2.0, Apache Sling Servlets Resolver 2.2.0, Apache Sling Adapter 2.1.0, Apache Sling Commons Testing 2.0.12 (November 15th, 2012)
  • New Release: Apache Sling JSP Taglib 2.1.8, Apache Sling Installer Core 3.4.0, Apache Sling Installer API 1.0.0, Apache Sling Installer Console 1.0.0, Apache Sling JCR Wrapper 2.0.0 (October 29th, 2012)
  • New Releases: Apache Sling Installer Core 3.3.8, Apache Sling Launchpad Installer 1.1.4, and Apache Sling Maven Launchpad Plugin 2.1.2 (August 19th, 2012)

History

Sling started as an internal project at Day Software, and entered the Apache Incubator in September 2007. As of June, 17th, 2009 Apache Sling is a top level project of the Apache Software Foundation.

The name "Sling" has been proposed by Roy Fielding who explained it like this:

[The name is] Biblical in nature. The story of David: the weapon he uses to slay the giant Goliath is a sling. Hence, our David's [David Nuescheler, CTO of Day Software] favorite weapon.

It is also the simplest device for delivering content very fast.

Who uses Sling?

See Who is using Sling on our public wiki.

Getting started

If you prefer doing rather than reading, please proceed to Discover Sling in 15 minutes or read through the recommended links in the Getting Started section, where you can quickly get started on your own instance of Sling.

Contents

Use Cases for Sling

Wiki

Day built a Wiki system on Sling. Each Wiki page is a node (with optional child nodes) in the repository. As a page is requested, the respective node is accessed and through the applying Component is rendered.

Thanks to the JCR Mapping and the resolution of the Component from the mapped Content, the system does not care for what actual node is addressed as long as there is a Content mapping and a Component capable of handling the Content.

Thus in the tradition of REST, the attachement of a Wiki page, which happens to be in a node nested below the wiki page node is easily accessed using the URL of the wiki page attaching the relative path of the attachement ode. The system resolves the URL to the attachement Content and just calls the attachement's Component to spool the attachement.

Digital Asset Management

Day has implemented a Digital Asset Management (DAM) Application based on Sling. Thanks to the flexibility of the Content/Component combo as well as the service registration/access functionality offered by OSGi, extending DAM for new content type is merely a matter of implementing one or two interfaces and registering the respective service(s).

Again, the managed assets may be easily spooled by directly accessing them.

Web Content Management

Last but not least, Sling offers itself very well to implementing a Web Content Management system. Thanks to the flexibility of rendering the output - remember: the system does not care what to render, as long as the URL resolves to a Content object for which a Component exists, which is called to render the Content - providing support for Web Content authors (not PHP programmers but users out in the field) to build pages to their likings can easily be done.

References

Apache Jackrabbit

The main purpose of Sling is to develop a content-centric Web Application framework for Java Content Repository (JCR) based data stores. Sling is implemented - with the notable exception of JCR Node Type management - purely in terms of the JCR API and as such may use any JCR compliant repository. The default implementation for Apache Jackrabbit is provided out of the box.

OSGi

Sling is implemented as a series of OSGi Bundles and makes extensive use of the OSGi functionality, such as lifecycle management and the service layer. In addition, Sling requires several OSGi compendium services to be available, such as the Log Service, Http Service, Configuration Admin Service, Metatype Service, and Declarative Services.

Apache Felix

While Sling does not require a specific OSGi framework implementation to run in, Sling is being developed using Apache Felix as the OSGi framework implementation. It has not been tested yet, but it is expected that Sling also operates perfectly inside other OSGi frameworks such as Equinox and Knopflerfish.

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