This is our first post in the Sling Gems series, that we'll use to demonstrate our favorite Sling features.
In this episode, the SlingPostServlet and the sling.js library are brought together using 46 (no kidding: fourty-six) lines of code to create a simple blog (or let's say bloggish) application.
I used this example in my Rapid JCR applications development with Sling presentation at the last ApacheCon (slides are available), and I think it's a good testimony to the power and simplicity of Sling.
Step 1: Creating content
The easiest way to create content in Sling is to use an HTTP POST request, let's use a simple HTML form to do that:
<html>
<body>
<h1>Sling microblog</h1>
<div>
<form method="POST">
Title:<br/>
<input type="text" name="title"
style="width:100%"/>
<br/>Text:<br/>
<textarea style="width:100%" name="text">
</textarea>
<br/>
<input type="submit" value="save"/>
<input type="hidden" name=":redirect"
value="*.html"/>
</form>
</div>
<!-- code of step 2 comes here -->
</body>
</html>
That's two input fields, a submit button and a hidden field that tells Sling what to do after the POST (in this case: redirect to the html view of the node that was just created).
To test the form, start Sling and save the above script as
/apps/blog/blog.esp in the Sling repository - a WebDAV mount
is the easiest way to do that. Browsing to
http://localhost:8888/content/blog/*.html2
should display the above form 4.
Input some data (using "foo" for the title, for the sake of our examples below), save the form, and Sling should display the form again, using the URL of the node that was just created.
At this point you're probably looking at an empty form with an URL ending in foo, if you used that for the title. Or foo_0 or foo_1 if other foos already existed. Don't worry about not seeing your content, we'll fix that right away.
Step 2: Where's my content?
To verify that our content has been created, we can have a look at the JSON
data at http://localhost:8888/content/blog/foo.tidy.json, which
should display our new node's values:
{
"jcr:primaryType": "nt:unstructured",
"text": "This is the foo text",
"title": "foo"
}
That's reassuring, but what we really want is for these values to be displayed on the editing form for our post.
Thanks to the sling.js client library, we just need to add a Sling.wizard()
call to our form to display those values. Let's first add a <head> element
to our form to load the sling.js library, before the existing <body> of course:
<head> <script src="/system/sling.js"></script> </head>
And add the Sling.wizard() after the form, where we
had the code of step 2 comes here comment:
<!-- code of step 2 comes here --> <script>Sling.wizard();</script>
Reloading the form at http://localhost:8888/content/blog/*.html and creating
a new post should now redirect to an editable version of the post, with the form fields
correctly initialized.
We can now create and edit posts; let's add some navigation, using more of the sling.js functionality.
Step 3: Navigation
The sling.js library provides utilities to access and manipulate content.
Four our blog, we'll use
the getContent(path) method to list the siblings of the current node.
Add the following code to your script, after the Sling.wizard() call that was added
in step 2:
<h3>Navigation</h3>
<ul>
<li><em><a href="/content/blog/*.html">
[Create new post]</a></em></li>
<script>
var posts =
Sling.getContent("/content/blog", 2);
for(var i in posts) {
document.write("<li>"
+ "<a href='/content/blog/" + i + ".html'>"
+ posts[i].title
+ "</a></li>");
}
</script>
</ul>
The first link to /content/blog/* brings us back to our content
creating form, which is nothing else than the editing form reading empty
values and posting to the "magic star" URL.
The rest of the javascript runs client-side, as it is not embedded in
<% %> code markers, calls the sling.getContent
method to get two levels of node data below /content/blog, and
displays links to nodes that it finds.
That's a basic navigation, of course, in a real blog we'd need some paging and contextualization to cope with large numbers of posts.
Nevertheless, with this addition our ESP script allows us to create, edit and navigate blog posts - not bad for 46 lines of code, including comments, whitespace and output formatting.
Step 4: Data first, structure later
You might have heard this mantra, which we apply in many areas of Sling.
In this case, adding a new field to our blog posts could not be easier: just add an input field to the form, and Sling will do the rest.
Adding this inside our script's <form> element, for example:
<br/>Author:<br/> <input type="author" name="author" style="width:100%"/>
Allows us to add an author name to our blog posts. No need to define anything at the repository level, as Sling is using it in unstructured mode in this case, and no need to migrate existing data, the author field of existing posts will simply be empty.
I want my ESP!
Now wait...we said we were going to create an ESP script, but our "application" is just static HTML and some client javascript at this point.
That's correct - as we are using only Sling client-facing features at this point
(HTTP POST and sling.js), we do not necessarily need to use ESP code.
To keep things simple, we'll refrain from adding ESP-based features at this point, and keep that for a future Sling Gem.
That's the power of Sling
The 46-line blog is a good example of the power of Sling. It leverages
the SlingPostServlet3, which handles POST requests in a
form-friendly way, and the sling.js
client library, which provides high-level functionality
on the client side.
A slightly fancier version of the blog.esp script is attached to this post, the code is the same but some CSS makes it look a bit nicer.
Let us know what you think, and stay tuned for more Sling Gems episodes!
http://localhost:8888/system/console/config, and save
that configuration.
I tried with a localhost version of sling but I couldn't get it to work. Looks like an authorization issue. I just grabbed the attachment and dropped it into the /apps/blog directory via WebDAV (using MacOSX 1.5). The form displays correctly but the form post appears to fail. Any idea what might be going on here and how I get around it?
http://localhost:8888/content/blog/*.json
Error while processing /content/blog/dog
Status
500
Message
javax.jcr.AccessDeniedException: /: not allowed to modify item
Location /blog/dog
Parent Location /blog
Path
/content/blog/dog
Referer http://localhost:8888/content/blog/*.html
ChangeLog
created("/content");
created("/content/blog");
created("/content/blog/dog");
modified("/content/blog/dog/text");
modified("/content/blog/dog/title");
Go Back
Modified Resource
Parent of Modified Resource
But the location was http://localhost:8888/system/console/configMgr, not config (sorry...I don't yet know my way around the OSGI console.
- Cris
The requested URL /blog/*/ resulted in an error in org.apache.sling.servlets.get.DefaultGetServlet.
ApacheSling/2.0 (Java HotSpot(TM) Client VM 1.5.0_16; Mac OS X 10.5.6 i386)
Is this just a typo in the attachment or is there some other setting I should be altering?
- Cris
Resource dumped by HtmlRendererServlet
Resource path: /content/*
Resource metadata: {sling.resolutionPath=/content/*, sling.resolutionPathInfo=.html}
Resource Value:
Any idea why?
1) Double-check that the blog script is indeed stored under /apps/blog/blog.esp in the repository (case-sensitive), for example by requesting http://localhost:8888/apps/blog/blog.esp which should display it.
2) The org.apache.sling.samples.path-based.rtp bundle must be active, the easiest way to check is via the http://localhost:8888/system/console/config page, search for "org.apache.sling.samples.path-based.rtp" there. If not, you can build it from http://svn.apache.org/repos/asf/incubator/sling/trunk/samples/path-based-rtp. I just noticed that it seems to be missing in the latest Sling trunk launchpad builds, I'll investigate. This bundle is what maps /content/blog/*.html to the "blog" resource type.
3) The ESP scripting engine must be active, look at the http://localhost:8888/system/console/scriptengines console page, which should include the "Apache Sling Scripting JavaScript Support" engine.
It doesn't appear that sling.js is available in the latest sling trunk either. Where can I get that file?
It doesn't appear that sling.js is available in the latest sling trunk either. Where can I get that file?
in the Sling trunk the file Sling.js is in bundles/servlets/post/src/main/resources/system
After I do footnote 4, all I get is HTTP ERROR 200 for every page with Reason: OK
Which means now I can't use the config page to undo this.
The title of : a blog in 46 lines of code lured me in, but I've had to do so many steps already (downloading, compiling, googling, more downloading ...) and still can't get this to work.
What exactly is the advantage of Apache Swing over using something like Caucho Resin with webdav enabled (I can add other languages like Groovy etc.)?
Add this to your query string:
sling:authRequestLogin=1
I had to adapt the code in rendering post title for new posts, as currentNode was not defined (1 extra line), otherwise it works nicely.