Discover Sling in 15 minutes

The Sling Launchpad is a ready-to-run Sling configuration, providing an embedded JCR content repository and web server, a selection of Sling components, documentation and examples. The Launchpad makes it easy to get started with Sling and to develop script-based applications.

This page will help you get started with the Launchpad. Fifteen minutes should be enough to get an overview of what Sling does.

While simple to run and understand, the Launchpad is a full-featured instance of Sling, an example configuration that we have created with the most common modules and configurations. The full functionality of Sling is available by loading additional Sling (or custom) OSGi bundles as needed, using the Launchpad's web-based OSGi management console.

See Also¶

More Sling samples can be found under http://svn.apache.org/repos/asf/sling/trunk/samples/

Once you grok the basic examples of this page, we recommend studying the slingbucks and espblog samples. Both have README files with more info.

Prerequisites¶

We'll start with the self-runnable jar from the Sling distribution, you only need a Java 7 JDK. Download the latest release from the Sling Downloads page or by clicking this link: org.apache.sling.launchpad-8.jar. Alternatively you can deploy the Sling Web application into any decent Servlet Container such as Jetty or Tomcat or you can build the current source yourself.

To show the simplicity of the REST-style approach taken by Sling the examples below will be using cURL. Any HTTP client would do, but cURL is the easiest to document in a reproducible way.

A WebDAV client makes editing server-side scripts much more convenient, but to make our examples easy to reproduce, we're using cURL below to create and update files in the JCR repository, via the Sling WebDAV server.

Start the Launchpad¶

After downloading the Sling Launchpad self-runnable jar just start it as follows:

$ java -jar org.apache.sling.launchpad-8.jar

This starts the Sling embedded Web Server on port 8080 and writes application files into the sling folder found in the current working directory.

Once started, look at http://localhost:8080/system/console/bundles with your browser. Use admin with password admin if Sling asks you for a login. Sling then displays the Felix Web Management Console page.

On the bundles page, all bundles should be marked Active. They're all OSGi bundles powered by Apache Felix, but that doesn't really matter to us right now.

Log files: If things go wrong, have a look at the sling/logs/error.log log file - that's where Sling writes any error messages.

Create some content¶

Until we have ready-to-test forms, you can create content with cURL, or you can create an HTML form that posts to the specified URL.

To create a content node (nodes are a JCR concept, a unit of storage) with cURL, use:

curl -u admin:admin -F"sling:resourceType=foo/bar" -F"title=some title" http://localhost:8080/content/mynode

The resulting node can be seen at http://localhost:8080/content/mynode.html, or as json format under http://localhost:8080/content/mynode.json. Lets try with cURL:

$ curl http://localhost:8080/content/mynode.json

This returns the properties of the /content/mynode in JSON format as we have created it above.

{"title":"some title","sling:resourceType":"foo/bar","jcr:primaryType":"nt:unstructured"}

The additional property jcr:primaryType is a special JCR property added by the content repository, indicating the JCR primary node type.

Monitoring requests: Sling provides a simple tool (an OSGi console plugin) to monitor HTTP requests, which helps understand how things work internally. See the Monitoring Requests page for details.

Render your content using server-side javascript (ESP)¶

Sling uses scripts or servlets to render and process content.

Several scripting languages are available as additional Sling modules (packaged as OSGi bundles that can be installed via the Sling management console), but the launchpad currently includes the ESP (server-side ECMAscript), JSP (Java Server Pages), and Groovy language modules by default.

To select a script, Sling uses the node's sling:resourceType property, if it is set.

That is the case in our example, so the following script will be used by Sling to render the node in HTML, if the script is found at /apps/foo/bar/html.esp in the repository.

<html>
  <body>
    <h1><%= currentNode.title %></h1>
  </body>
</html>

To select the script, Sling:

• looks under /apps
• and appends the sling:resourceType value of our node ( which is foo/bar )
• and appends html.esp, as the extension of our URL is html and the language of our script is esp.

Store this script under /apps/foo/bar/html.esp, either using a WebDAV client (connected to http://admin:admin@localhost:8080/), or using cURL as shown here, after creating the html.esp script in the current directory on your system:

curl -X MKCOL -u admin:admin http://localhost:8080/apps/foo
curl -X MKCOL -u admin:admin http://localhost:8080/apps/foo/bar

create a local file html.esp and copy above content.

curl -u admin:admin -T html.esp http://localhost:8080/apps/foo/bar/html.esp

The HTML rendering of your node, at http://localhost:8080/content/mynode.html, is now created by this ESP script. You should see the node's title alone as an <h1> element in that page.

A script named POST.esp instead of html.esp would be called for a POST request, DELETE.esp for DELETE, xml.esp for a GET request with a .xml extension, etc. See URL to Script Resolution on the Sling wiki for more info.

Servlets can also be easily "wired" to handle specific resource types, extensions, etc., in the simplest case by using SCR annotations in the servlet source code. Servlets and scripts are interchangeable when it comes to processing Sling requests.

What next?¶

These simple examples show how Sling uses scripts to work with JCR data, based on sling:resourceType or node types.

There's much more to Sling of course - you'll find some additional simple examples below, as well as above in the see also section.

Additional examples¶

Let Sling generate the path of a newly created node.¶

To create a node with a unique path at a given location, end the URL of the POST request with /.

In this case, the Sling response redirects to the URL of the created node.

Start by creating a new /blog folder:

curl -X POST -u admin:admin "http://localhost:8080/content/blog"

And create a node with a Sling-generated name under it:

curl -D - -u admin:admin -F"title=Adventures with Sling" "http://localhost:8080/content/blog/"

Using cURL's -D option shows the full HTTP response, which includes a Location header to indicate where the new node was created:

Location: /blog/adventures_with_slin

The actual node name might not be adventures_with_slin - depending on existing content in your repository, Sling will find a unique name for this new node, based on several well-know property values like title, description, etc. which are used for this if provided.

So, in our case, our new node can be displayed in HTML via the http://localhost:8080/blog/adventures_with_slin.html URL.

Note that we didn't set a sling:resourceType property on our node, so if you want to render that node with a script, you'll have to store the script under /apps/nt/unstructured/html.esp.

Add a page header with sling.include¶

The sling.include function can be called from scripts to include the rendered result of another node.

In this example, we create a node at /content/header, rendered with a logo using an html.esp script, then use that header at the top of the html.esp script that we created previously for the foo/bar resource type.

Start by checking that http://localhost:8080/content/mynode.html is rendered using the html.esp script created above.

Create this script and name it header.esp:

<div>
  <p style="color:blue;">
    <img src="/images/sling.jpg" align="right"/>
    <%= currentNode.headline %>
  </p>
</div>

Upload it so that it is used to render resources having sling:resourceType=foo/header:

curl -X MKCOL -u admin:admin http://localhost:8080/apps/foo/header/
curl -u admin:admin -T header.esp http://localhost:8080/apps/foo/header/html.esp

Create the header node:

curl -u admin:admin -F"sling:resourceType=foo/header" -F"headline=Hello, Sling world" http://localhost:8080/content/header

Upload the logo that the script uses (using sling.jpg or another logo in the current directory):

curl -X MKCOL -u admin:admin http://localhost:8080/images/
curl -u admin:admin -T sling.jpg http://localhost:8080/images/sling.jpg

And check that the header is rendered with the logo at http://localhost:8080/content/header.html.

Now, update the html.esp script that we created for our first example above, to include the header:

<html>
  <body>
    <div id="header">
      <% sling.include("/content/header"); %>
    </div>
    <h1><%= currentNode.title %></h1>
  </body>
</html>

And upload it again to replace the previous version:

curl -u admin:admin -T html.esp http://localhost:8080/apps/foo/bar/html.esp

The http://localhost:8080/content/mynode.html, once refreshed, now shows the blue headline and logo, and this layout also applies to any node created with sling:resourceType=foo/bar.