Insane Programming Java ramblings and finds on the net

Doing RPC with REST

RPC doesn't really rhyme with REST. REST revolves around the concept of resources, and the basic methods offered by the HTTP protocol (being GET, PUT, POST, DELETE and some others). Now, sometimes you're confronted with something outside the scope of those methods. Say, for example, you want to be able to send a client's data to the ERP system by simply doing 1 REST call.
Option 1 is to create an URL template like this: http://host/client/{id}/sendToERP. But that isn't REST. sendToERP isn't a resource, it's an action. So that one's gone.
Option 2 is to create an URL template like this: http://host/client/{id}?action=sendToERP. Better, but to which HTTP method will you bind this. Is it a GET? A PUT? Not really sure. You're not really altering the client, but you're not asking for the data either...
So that brings us to option 3: the command pattern. Assume we have a URL template like this: http://host/client/{id}/command. Doing a get on this will return all the possible commands for that client. In our case this might be:

<commands>
  <command id="1">
    <type>sendToERP</type>
  </command>
  <command id="2">
    <type>updateFromERP</type>
  </command>
</commands>

So now we can do this to execute the sendToERP command: GET http://host/client/{id}/command/1. What does this return? Well, it can for example return the result of the command, like this:

<commandResult>
  <result>
     OK
  </result>
</commandResult>