Applying REST principles to a complex Enterprise is harder than applying them to a photo-database or a blog-site (aka skinned database). No points for that one. Why do it? Well treating an Enterprise as a set of ‘resources’ with representations and behavioural contracts applied to attributes manipulated through a uniform, ubiquitous interface is a liberating experience on the design-slab. However when we come to take real steps we are beset by 2 key obstacles:
Resource representations are abstractions of a complex information architecture underpinned by many diverse and evolving IT assets, so we do not have atomic control over the assembly of resource representations nor do we have atomic control over key-mastering and complex updates.
The resource Namespace needs to support hierarchy to ensure we can correctly structure context around certain resource-types who’s representations may be context-aware. As such depending on who is looking at what, there is a complex resolution of the public namespace to a potentially complex EAI landscape within the black-box.
Are these problems insurmountable? Well I don’t believe so, but the resulting shape of the framework I’d use to achieve this is significantly different to the emerging frameworks (i.e. JAX-RS/JSR311, Restlet, etc) geared towards resource-enabling stuff. Why?
The primary reason why I seem to be diverging from the direction being taken by the framework guys, is simply that (…note to self…I’m not officially recognising options which would require me to acknowledge that I’m being stoopid ) I need more dynamic processing in the mapping of a requested URI to a POJO/Controller. What does this mean?
Well – based on the 2 points I outlined at the start of this article the inspection, validation and refinement of my inbound URI’s are managed within a single control step, fed with meta-data and context info. Similarly, as I resolve a canonical resource (i.e. one which may be reached through a range of public namespace paths) I need to work out how best to ‘go and execute’ the require data-acquisition or functional RPC steps to implement the resource operation. Again – another control step fed with meta-data and context info.
What I end up with, is a processing chain from HTTP request through to Enterprise resource, where the namespace, URI resolution and method variations are simply parameters driving a more complex, dynamic integration broker. As I DRY up my code, I begin to refactor away from having explicit resource controllers be that at a class-oriented or annotation-based level.
Ultimately my ideal ‘REST’ framework is one which enables me to data-drive not only the production of a resource facade, but the linkages between those resources and complex integration/aggregation transactions, therefore imploding the more explicit genre of ‘REST framework’ in favour of a declarative alterative.
At this time I’m prototyping with SpringMVC Servlet/Interceptors and also raw Servlet/Filter chains, both of which are configured to have only 1 front-controller, and a series of processing steps as the inbound request is boiled down to a back-end transaction. The bulk of the manifestation of REST-oriented logic is meta-data consulted by the processing chain within the context of a user-initiated operation.
This is what I mean by Implosion of REST frameworks…