When should I use RequestFactory vs GWT-RPC?
I am trying to figure out if I should migrate my gwt-rpc calls to the new GWT2.1 RequestFactory cals.
Google documentation vaguely mentions that RequestFactory is a better client-server communication method for "data-oriented services"
What I can distill from the documentation is that there is a new Proxy class that simplifies the communication (you don't pass back and forth the actual entity but just the proxy, so it is lighter weight and easier to manage)
Is that the whole point or am I missing something else in the big picture?
Answer
The big difference between GWT RPC and RequestFactory is that the RPC system is "RPC-by-concrete-type" while RequestFactory is "RPC-by-interface".
RPC is more convenient to get started with, because you write fewer lines of code and use the same class on both the client and the server. You might create a Person class with a bunch of getters and setters and maybe some simple business logic for further slicing-and-dicing of the data in the Person object. This works quite well until you wind up wanting to have server-specific, non-GWT-compatible, code inside your class. Because the RPC system is based on having the same concrete type on both the client and the server, you can hit a complexity wall based on the capabilities of your GWT client.
To get around the use of incompatible code, many users wind up creating a peer PersonDTO that shadows the real Person object used on the server. The PersonDTO just has a subset of the getters and setters of the server-side, "domain", Person object. Now you have to write code that marshalls data between the Person and PersonDTO object and all other object types that you want to pass to the client.
RequestFactory starts off by assuming that your domain objects aren't going to be GWT-compatible. You simply declare the properties that should be read and written by the client code in a Proxy interface, and the RequestFactory server components take care of marshaling the data and invoking your service methods. For applications that have a well-defined concept of "Entities" or "Objects with identity and version", the EntityProxy type is used to expose the persistent identity semantics of your data to the client code. Simple objects are mapped using the ValueProxy type.
With RequestFactory, you pay an up-front startup cost to accommodate more complicated systems than GWT RPC easily supports. RequestFactory's ServiceLayer provides significantly more hooks to customize its behavior by adding ServiceLayerDecorator instances.