Re: Sketch of updated APIs (was Re: Redirection and creation)

From: Marc Hadley <Marc.Hadley_at_Sun.COM>
Date: Tue, 17 Apr 2007 14:14:57 -0400

On Apr 16, 2007, at 11:39 AM, Marc Hadley wrote:
> - Reworked Representation and HttpResponse to use annotations to
> mark their properties as I'd outlined earlier in the thread.
> Essentially the representation and response classes become "pre-
> baked" instances of return types but the annotation approach allows
> an application to use their own classes instead if they so wish.
There are a few things that bother me about this approach:

(i) Performance - an implementation would have to do a *lot* of
reflection to extract the metadata. Each field and bean getter will
have to be checked for each of the metadata annotations we define
and, because annotations on methods are not inherited, an
implementation would also have to walk the inheritance hierarchy to
look for metadata annotations on superclasses too.

(ii) Complexity - the specification will need to define rules for co-
occurrence, cardinality, inheritance and overriding for each of the
metadata annotations. Rules may turn out to be different for
different annotations. E.g. one would expect it to be an error to
have multiple @HttpStatus annotations on a bean but it would OK to
have multiple @HttpHeader annotations, possibly even multiple for the
same header depending on the header. The specification will also need
to define precedence rules where the metadata can be obtained from
multiple sources

(iii) Benefit - the usefulness of this approach hinges on whether it
will be common for existing application classes to have fields or
properties that map directly to HTTP metadata. E.g. will it be common
for an application class to have an existing field or property that
provides the HTTP status code for a response that contains the data
encapsulated by the class. Personally I find this quite unlikely:
even looking at something like the ROME library classes for the Atom
format one finds gaps where additional metadata would be required. I
suspect that many application classes will be quite devoid of HTTP
metadata and that the primary use of the JSR 311 API will be to
develop RESTful facades to existing application data classes.

Thoughts, comments ?

Marc Hadley <marc.hadley at>
CTO Office, Sun Microsystems.