Apache Sling CMS

Apache Sling is a framework for RESTful web applications based on an extensible content tree, and it is important to be clear about what that means before evaluating it: Sling is not a packaged content management system with an authoring interface. It is the foundation on which such systems are built, and the project states directly that it serves as the basis for applications ranging from blogging engines through to enterprise content management systems. Choosing it means building, not installing.

The architectural idea is genuinely distinctive. Sling maps HTTP request URLs to content resources based on the request path, extension and selectors, so the content tree determines what handles a request rather than a routing configuration. Following convention over configuration, requests are processed by scripts and servlets that are selected dynamically based on the current resource. The consequences the project claims are meaningful URLs and resource driven request processing, which in practice means URL structure and content structure stay aligned rather than drifting apart as a site grows.

Modularity is the other defining property. Sling's modular nature allows specialised server instances that include only what is needed, so a deployment carries only the bundles required rather than a full platform footprint. This is why it underpins products with very different requirements. As an Apache Software Foundation project it is open source and free, with development in the open. Documentation covers an overview, getting started, the Sling engine, development, bundles, tutorials, how-tos, Maven plugins, configuration and API docs, with versioned documentation maintained back through Sling 11. Discussion happens on mailing lists, and downloads, release notes, an issue tracker and source repositories are published.