good practise: REST API as the interface between the interface layer and business layer?

Question

I was thinking about the architecture of a web application that I am planning on building and I found myself thinking a lot about a core part of the application. Since I will want to create, for example, an android application to access it, I was already thinking about having an API.

Given the fact that I will want to have an external API to my application from day one, is it a good idea to use that API as an interface between the interface layer (web) and the business layer of my application? This means that even the main interface of my application would access the data through the API. What are the downsides of this approach? performance?

In more general terms, if one is building a web application that is likely to need to be accessed in different ways, is it a good architectural design to have an API (web service) as the interface between the interface layer and business layer? Is REST a good "tool" for that?

Answer 1

Sure, REST could be used for that. But first ask yourself, does it make sense? REST is a tool like any other, and while a good one, not always the best hammer for every nail. The advantage of building this interface RESTfully is that, IMO, it will make it easier in the future to create other uses for this data - maybe something you haven't thought of yet. If you decide to go with a REST API your next question is, what language will it speak? I've found AtomPub to be a great way for processes/applications to exchange info - and it's very extensible so you can add a lot of custom metadata and yet still be eaily parsed with any Atom libraries. Microsoft uses AtomPub in it's cloud [Azure] platform to talk between the data producers and consumers. Just a thought.

Answer 2

My recent preference, which is based on J2EE6, is to implement the business logic in session beans and then add SOAP and RESTful web services as needed. It's very simple to add the glue to implement the web services around those session beans. That way I can provide the service that makes the most sense for a particular user application.

Answer 3

You will definitely need need a Web Service layer if you're going to be accessing it from a native client over the Internet.

There are obviously many approaches and solutions to achieve this however I consider the correct architectural guideline to follow is to have a well-defined Service Interface on the Server which is accessed by the Gateway on the client. You would then use POCO DTO's (Plain old DTO's) to communicate between the endpoints. The DTO's main purpose is to provide optimal representation of your web service over the wire, it also allows you to avoid having to deal with serialization as it should be handled transparently by the Client Gateway and Service Interface libraries.

It really depends on how to big your project / app is whether or not you want want to go through the effort to mapping your DTO's to the client and server domain models. For large applications the general approach would be on the client to map your DTO's to your UI Models and have your UI Views bind to that. On the server you would map your DTO's to your domain models and depending on the implementation of the service persist that.

REST is an architectural pattern which for small projects I consider an additional overhead/complexity as it is not as good programattic fit compared to RPC / Document Centric web services. In not so many words the general idea of REST is to develop your services around resources. These resources can have multiple representations which your web service should provide depending on the preferred Content-Type indicated by your HTTP Client (i.e. in the HTTP ACCEPT HEADER). The canonical urls for your web services should also be logically formed (e.g. /customers/reports/1 as opposed to /GetCustomerReports?Id=1) and your web services would ideally return the list of 'valid states your client can enter' with each response. Basically REST is a nice approach promoting a loosely-coupled architecture and re-use however requires more effort to 'adhere' to than standard RPC/Document based web services whose benefits are unlikely to be visible in small projects.

If you're still evaluating what web service technology you should use, you may want to consider using my open source web framework as it is optimized for this task. The DTO's that you use to define your web services interface with can be re-used on the client (which is not normally the case) to provide a strongly-typed interface where all the serialization is taken for you. It also has the added benefit of enabling each web service you create to be called by SOAP 1.1/1.2, XML and JSON web services automatically without any extra configuration so you can choose the most optimal end point for every client scenario, i.e. Native Desktop or Web App, etc.

Answer 4

We've had good luck doing something like this on a project. Our web services mainly do standard content management, with a high proportion of reads (GET) to writes (PUT, POST, DELETE). So if your logic layer is similar, this is a very reasonable approach to consider.

In one case, we have a video player app on Android (Motorola Droid, Droid 2, Droid X, ...) which is supported by a set of REST web services off in the cloud. These expose a catalog of video on demand content, enable video session setup and tear-down, handle bookmarking, and so on. REST worked out very well for this.

For us one of the key advantages of REST is scalability: since RESTful GET responses may be cached in the HTTP infrastructure, many more clients can be served from the same web application.

But REST doesn't seem to fit some kinds of business logic very well. For instance in one case I wrapped a daily maintenance operation behind a web service API. It wasn't obvious what verb to use, since this operation read data from a remote source, used it to do a lot of creates and updates to a local database, then did deletes of old data, then went off and told an external system to do stuff. So I settled on making this a POST, making this part of the API non-RESTful. Even so, by having a web services layer on top of this operation, we can run the daily script on a timer, run it in response to some external event, and/or have it run as part of a higher level workflow.

Since you're using Android, take a look at the Java Restlet Framework. There's a Restlet edition supporting Android. The director of engineering at Overstock.com raved about it to me a few years ago, and everything he told us was true, it's a phenomenally well-done framework that makes things easy.

Answer 5

Sounds like you've got two questions there, so my answer is in two parts.

Firstly, should you use an API between the interface layer and the business layer? This is certainly a valid approach, one that I'm using in my current project, but you'll have to decide on the benefits yourself, because only you know your project. Possibly the largest factor to consider is whether there will be enough different clients accessing the business layer to justify the extra development effort in developing an API? Often that simply means more than 1 client, as the benefits of having an API will be evident when you come to release changes or bug fixes. Also consider the added complexity, the extra code maintenance overhead and any benefits that might come from separating the interface and business layers such as increased testability.

Secondly, if you implement an API, should you use REST? REST is an architecture, which says as much about how the remainder of your application is developed as it does the API. It's no good defining resources at the API level that don't translate to the Business Layer. Rest tends to be a good approach when you want lots of people to be able to develop against your API (like NetFlix for example). In the case of my current project, we've gone for XML over HTTP, because we don't need the benefits that Rest generally offers (or SOAP for that matter).

In general, the rule of thumb is to implement the simplest solution that works, and without coding yourself into a corner, develop for today's requirements, not tomorrow's.

Chris