Discover Sling in 15 minutes - the Sling Launchpad
The Sling Launchpad is a ready-to-run Sling configuration, providing an embedded JCR content repository and web server, a selection of Sling components, and documentation and examples. The Launchpad makes it easy to get started with Sling and to develop script-based applications.
This page will help you in getting 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 modules as needed, using the Launchpad's web-based OSGi management console.
See Also
Example applications and mini-applications for Sling 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 espblog and webloader samples for more complete examples. The javashell sample is useful to play with JCR java code (or any java code, for that matter) interactively.
Prerequisites
If using the self-runnable jar from the Sling distribution, you only need a Java 5 JDK.
If using the war file from the Sling distribution, you need a suitable servlet container (all recent versions of Jetty or Tomcat should work), running under a Java 5 JDK.
If building Sling yourself (which is the best way to get the latest and greatest), you'll need:
- A Subversion client to get the Sling code.
- A Java 5 JDK.
- Maven for the build, we currently recommend V 2.0.7 (and see our MavenTipsAndTricks).
And in all cases you'll need cURL to run the examples below. 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.
Get the Launchpad
See Getting and Building Sling - you can either use a released version (if it is current enough), or build it yourself.
Start the Launchpad
If using the self-runnable jar from the Sling distribution, start it by double-clicking or with java -jar ....
If using the war file from the Sling distribution, install it in your servlet container and start that.
If you built Sling yourself, change to the launchpad/webapp directory under the top-level sling directory, and run
To start the launchpad.
The examples below assume that Sling is running on port 8080, which is the default for the launchpad/webapp module. If your setup is different you'll need to adjust the port number accordingly.
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 target/sling/logs/error.log log file under launchpad/webapp - 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:
The resulting node can be seen at http://localhost:8080/content/mynode.html, or as json format under http://localhost:8080/content/mynode.json.
![]() | 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 only includes the ESP (server-side ECMAscript) and JSP (Java Server Pages) languages modules by default.
To select a script, Sling uses the node's sling:resourceType property, if it is set.
That's 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, appends the sling:resourceType value of our node, which is foo/bar, and appends html.esp as the extension if 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:ad...@localhost:8080/), or using cURL as shown here, after creating the html.esp script in the current directory on your system:
create a local file html.esp and copy above content.
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, and above in the see also section.
We are working on debugging features to help trace the way Sling processes requests. Have a look at SLING-3 to see what's possible already.
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:
And create a node with a Sling-generated name under it:
Using cURL's -D option shows the full HTTP response, which includes a Location header to indicate where the new node was created:
The actual node name might not be adventures_with_slin_0 - 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/content/blog/adventures_with_slin_0.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, and use that header at the top of the html.esp script that we previously created 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="" class="code-quote">"/images/sling.jpg" align="right"/> <%= currentNode.headline %> </p> </div>
Upload it so that it is used to render resources having sling:resourceType=foo/header:
Create the header node:
Upload the logo that the script uses (using some sling.jpg or other logo in the current directory):
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 re-upload it to replace the previous version:
The http://localhost:8080/content/mynode.html, once refreshed, now shows the blue headline and logo, and that layout applies to any node created with sling:resourceType=foo/bar.
