What is the purpose behind building of Apache Sling, Felix, Jackrabbit projects

Question

I am asking a very basic question here.

Question is

I am using Apache Sling , Apache Jackrabbit, Apache Felix in my project as said by my in

Answer 1

Sling in very simple terms could be described as a REST API for JCR. you can use http requests to manage content inside the repository.

Additionally, Sling provides a mechanism to render that content in different ways for web consumption. you can use scripts (JSP for example) and the java code (servlets, pojos, etc) in the Felix container to process requests and deliver a request.

When a request is made for a particular node, Sling looks up for a property called sling:resourceType, this is a lookup key for rendering scripts. Then the appropiate script is executed using the node as input.

You could write different kinds for renderers and then use it to display your content in different ways.

For example, you could write two scripts full.json.jsp and short.json.jsp and then use them to render the same node in two different ways:

/content/app/node.full.json 

OR

/content/app/node.short.json.

Sling basically matches tokens in the request URL to select an appropriate script.

They have a really nice cheat sheet that explains how request resolution and rendering works

it is a bit more complex than this, since everything is organized in resources and components. you want to check their site for more info