J2ME and RESTful Web Service
I’m currently working on a project involving a J2ME client on a mobile phone connecting to a Rails RESTful web service. As you might know, a RESTful web service utilizes the four HTTP verbs GET, POST, PUT and DELETE.
Yesterday we started to write unit tests, running on a J2ME device, to check if the Rails web service conformed to our specifications, when suddenly we got this:
We had the web service specification finished, the Rails application was nearly finished, the J2ME web service adapter was finished, the J2ME GUI was underway - over 500 hours of work and suddenly this!
You can imagine our faces as we looked at the screen, reading the exception on the tiny display of the Nokia mobile phone emulator.
We went to the Sun site to get the sources of the J2ME MIDP2.0 reference implementation and found this:
Why the hell did they do that? Why are they restricting the HTTP verbs to HEAD, GET and POST? Security? Fun?
Luckily for us, there is also another widely deployed platform/application that only supports GET and POST: the browser!
So when Rails started to support RESTful controllers and routing, they had to invent a mechanism to piggyback PUT and DELETE requests on the POST method.
Rails solves this by using a hidden field in HTML forms named _method, but you can also specify _method as a URL parameter (given that you send a POST request):
Rails certainly intended this for the browser, but it also works with XML requests if you specify the method as a URL parameter, and it can save your life if you use J2ME - at least, it certainly saved us from a serious headache.
Thank you, Rails! And to you J2ME guys: please, remove those five idiotic lines - there are more verbs than those three.
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