back to the beginning ... construct

I had a couple of constructive discussions after my last post. A couple of doubts were raised about the reality of what I said.

There's only one way to answer those doubts and that is by showing you. So when I was revising some stuff for a customer earlier this week, I reconstructed one component for discussion here. Before I go into the details (and show you where you can find it), allow me to say a couple of words about APIs on the Internet.

Well, like most of the Apis mellifera family, APIs on the Internet have quite a sting but unlike bees, they regularly sting again (wasp like), as anybody trying to keep up with the Google, Facebook, Twitter, Dropbox, <you name it>, APIs can attest to.

However, for all their perceived flaws (which I won't go into) they are a step towards a programmable web and I deal with them on a frequent basis. What I typically do in order to use them is construct a component that :
  1. Shields the complexity.
  2. Constrains the usage.
  3. Improves the caching.
As an example, I created the urn.com.elbeesee.api.rovi module which is now available on Github. The Rovi (http://developer.rovicorp.com) API provides metadata for movies and music products.

Note that I only provided the source, if you want to use it you'll have to build the Java code. If this is making too much of an assumption on my part, contact me and I'll walk you through, no problem. If I get lots of requests, I'll blog about that next time.

You'll notice that the module provides two accessors, one - active:rovimd5 is private and computes the signature necessary to make requests. The other one active:rovirelease is public and takes a upcid as argument and provides access to the Rovi Release API.

In order to use active:rovirelease it needs to be able to find three resources when you issue a request to it, rovi:apikey, rovi:secretkey and rovi:expiry.

The first two are obvious and it is obvious why I'm not providing those in the module itself. The third one may be less obvious, but you'll note the following in the code :

rovireleaserequest.setHeader("exclude-dependencies",true); // we'll determine cachebility ourselves

When making the actual request to Rovi I ignore any caching directives that come my way. And on the response I do the following :

vResponse.setExpiry(INKFResponse.EXPIRY_MIN_CONSTANT_DEPENDENT, System.currentTimeMillis() + vRoviExpiry);

Two questions that can be raised about this are :
  1. Why are you doing this ?
  2. Is this legal ?
The Why is easy to answer. It is my business logic that should decide how quickly it wants updates, not a 3rd party API that wants to make money out of my requests. 

The legal aspect is not so clear and you should carefully read what the terms of usage are. Note however that I am not persisting any results from the API, I'm just letting the business logic dictate how long they are relevant in memory (and since memory is limited the distribution of the requests will determine which results remain in memory and which do not).

Adding persistence would not be very hard, however especially for paying services you then need to be fully aware of the terms of usage. Contact me for details if you want to know how to add a persistence layer.

Another takeaway from this module is that I throttle active:rovirelease. Granted, this is maybe also something that shouldn't be done in there (as it may depend on your business model) but controlling the flow is an important aspect of using APIs and this is a - simple - way to do it.

A last takeaway is that I don't interpret the result of the request in this component, nor do I force it into a format of any kind. And while I will grant that adding some form of handling could be useful after the actual API call it is an important takeaway. This component shields the API. What is done with the result belongs in another component.

This component is used in production. It is reality. You'll also find that it doesn't contain any kind of magic or clever coding (or a lot of coding at all). And yet it accomplishes quite a few things. The main thing it accomplishes is that it turns an API not under your control into a resource that is.