[CONF] Apache Sling: Discover Sling in 15 minutes (page edited)

confluence Thu, 28 May 2009 06:44:36 -0700

Page Edited : SLING : Discover Sling in 15 minutes

Discover Sling in 15 minutes has been edited by Benjamin Francisoud (May 28, 2009).

Change summary:

remove "MKCOL apps", returns 405 because it alreday exists in default war distribution

(View changes)

Content:

Discover Sling in 15 minutes - the Sling Launchpad

Page Status

Reviewed 2009-09-24, this page's information is in sync with the current Sling codebase.

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.

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

mvn jetty:run

To start the launchpad.

The examples below assume that Sling is running on port 8888, 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:8888/system/console with your browser. Use admin with password admin if Sling asks you for a login. Sling then displays the Sling Management Console page.

We don't need the Sling management console right now, but it tells us that Sling is started.

If you look at the http://localhost:8888/system/console/list page, all bundles should be marked Active. They're 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:

curl -F"sling:resourceType=foo/bar" -F"title=some title" http://admin:ad...@localhost:8888/content/mynode

The resulting node can be seen at http://localhost:8888/content/mynode, with default renderings in various formats at http://localhost:8888/content/mynode.html and http://localhost:8888/content/mynode.tidy.json.

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.esp

<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:8888/), or using cURL as shown here, after creating the html.esp script in the current directory on your system:

curl -X MKCOL http://admin:ad...@localhost:8888/apps/foo
curl -X MKCOL http://admin:ad...@localhost:8888/apps/foo/bar
curl -T html.esp http://admin:ad...@localhost:8888/apps/foo/bar/html.esp

The HTML rendering of your node, at http://localhost:8888/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:

curl -X POST "http://admin:ad...@localhost:8888/content/blog"

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

curl -D - -F"title=Adventures with Sling" "http://admin:ad...@localhost:8888/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: http://localhost:8888/content/blog/adventures_with_slin_0

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:8888/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:8888/content/mynode.html is rendered using the html.esp script created above.

Create this script and name it header.esp:

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:

curl -X MKCOL  http://admin:ad...@localhost:8888/apps/foo/header/
curl -T header.esp http://admin:ad...@localhost:8888/apps/foo/header/html.esp

Create the header node:

curl -F"sling:resourceType=foo/header" -F"headline=Hello, Sling world" http://admin:ad...@localhost:8888/content/header

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

curl -X MKCOL  http://admin:ad...@localhost:8888/images/
curl -T sling.jpg  http://admin:ad...@localhost:8888/images/sling.jpg

And check that the header is rendered with the logo at http://localhost:8888/content/header.html.

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