URI Templates can make interacting with the web APIs like the Facebook Graph API a little easier. Here, I’ll show you how you can use URI Templates to create request URIs into the Facebook Graph API using the Handy URI Templates library. The URI Template examples described should be usable by any RFC6570 URI Template processor, but I’ll be focusing on how to use the Handy URI Templates API in Java. If you’re using PHP, have a look at Michael Dowling’s excellent Guzzle Framework which has great URI template support.
URI Template Basics
We’ll assume you have some familiarity with URI templates. Basically, a URI template is expression where replacement variables are identified by the text between ‘{‘ and ‘}’, like so:
https://graph.facebook.com/{id}
Where {id} is the name of the variable. This is similar to how paths are expressed in JAX-RS, and OpenSearch URL template syntax . The RFC6570 spec provides a lot more details on the URI template standard syntax, so we’ll focus on how to use URI templates in conjunction with the Facebook Graph API.
Facebook Graph API Basics
For the most part, most URIs in the Graph API follow the basic pattern of hostname + id. In a URI template, this pattern can be expresed as:
https://graph.facebook.com/{id}
When the template variable is expanded, it will allow you to create URIs that can be used request resources like so:
And so on. Facebook also requires you to supply the access_token in a query parameter on the request URI, so now we end up with the expression:
https://graph.facebook.com/{id}{?access_token}
Please check the Facebook documenation on how to get the token.
Using the Handy URI Templates API, you can create a URI from an expression like so:
String expression = "https://graph.facebook.com/{id}{?access_token}";
String uri =
UriTemplate.fromExpression(expression)
.set("id", "bgolub")
.set("access_token", System.getProperty("fb.access_token"))
.expand();
This will give you the following URI:
https://graph.facebook.com/bgolub?access_token=your_fb_access_token
Because the {id} variable can contain sub paths, we need a way to express that. If we have want to express a URI template that gets a users information or the users photo albums, we need additional path segements. We could use multiple path segments with more variables, but this can make the template more complicated. One option is to modify the expression so that {id} can accomodate a single path segement or multiple path segments by rewriting the expression as:
https://graph.facebook.com{/id*}{?access_token}
This does a few things:
- By putting the path ‘/’ operator in the variable expression, we’re stating that the values in this variable path segements. By default, if the variable values is an array, Collection or Map, the values will be ‘,’ delimited.
- The
* modifier means ‘explode’. With an array or Collection plus the explode modifier, the values will be delimited by the ‘/’ operator.
Now if we change the code a little bit:
String expression = "https://graph.facebook.com{/id*}{?access_token}";
String uri =
UriTemplate.fromExpression(expression)
.set("id", new String[] {"bgolub","albums"})
.set("access_token", System.getProperty("fb.access_token"))
.expand();
You’ll note that the value we pass to the id variable is an array of strings and the processor will render valuse as two strings separated by a /.The resulting URI is now:
https://graph.facebook.com/bgolub/albums?access_token=your_fb_access_token
Now lets see how we can make more advanced types of requests.
More Advanced Requests
The Graph API has a number of query parameters that modifiy the request. All of these are defined in the Facebook Graph API documenation so I won’t detail them here. With all of the query parameters collected, you end up with the following URI template expression:
https://graph.facebook.com{/id*}{?q,ids,fields,type,center,distance,limit,offset,until,since,access_token}
You can pretty much use this template express for the majority, if not all, of the Facebook Graph API. We’ll use that expression for rest of the examples.
Search Request URIs
With the URI template, we can create URIs that map to Graph API search requests. Using the “coffe” example from the Facebook documenation:
String expression = "https://graph.facebook.com{/id*}{?q,ids,fields,type,center,distance,limit,offset,until,since,access_token}";
String uri =
UriTemplate.fromExpression(expression)
.set("id","search")
.set("q", "coffee")
.set("type","place")
.set("center", new float[] {37.76f,-122.427f})
.set("distance", 1000)
.set("limit", 5)
.set("offset", 10)
.set("access_token", System.getProperty("fb.access_token"))
.expand();
This will give us the URI:
https://graph.facebook.com/search?q=coffee&type=place¢er=37.76,-122.427&distance=1000&limit=5&offset=10&access_token=your_access_token
Note how the variables until and since are not included in the expanded URI.
FQL Request URIs
Even things URIs with FQL queries can be expressed in a template. Give our code:
String expression = "https://graph.facebook.com{/id*}{?q,ids,fields,type,center,distance,limit,offset,until,since,access_token}";
String uri =
UriTemplate.fromExpression(expression)
.set("id","fql")
.set("q", "SELECT uid2 FROM friend WHERE uid1=me()")
.set("access_token", System.getProperty("fb.access_token"))
.expand();
Wrap Up
Hopefully this gives you a good idea on both how to use URI Templates in general, and a good insight into how you can use teh Handy URI Templates API. If you want more exmaples, have a look at the code on GitHub here. There are examples for Facebook, Twitter, and GitHub.
Damnhandy 
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