Module 13: Creating a Facebook Clone
Once the service layer exists, the web-service layer should be boring. That is not a criticism. It is a sign that the architecture is doing its job.
This lesson demonstrates that well. UserWebService is mostly a translation layer. It defines URLs, request shapes, headers, and response behavior, then hands the real work off to the service classes underneath. That is exactly what controllers should look like in a healthy backend.
The exception-to-error-DAO mapping is one of the most important parts here. It gives the client a predictable error contract instead of exposing raw Java exceptions or framework defaults. Even simple apps benefit from that discipline because it keeps client-side error handling from becoming guesswork.
The avatar endpoints are a good example of the controller layer adding protocol-specific behavior without swallowing business logic. They return image content with the right response metadata, turn missing avatars into 404 semantics, and still leave the real authorization and data retrieval rules to the service layer.
The lesson also makes a pragmatic choice in a few places by using GET operations for state changes when the mobile client benefits from simpler calling code. That is not something I would present as ideal REST design today. It works here because the client is controlled, but the general rule should still be to avoid using GET for operations that mutate state.
So the right takeaway is not “copy these HTTP verbs literally.” It is “keep the controller thin, explicit, and responsible only for transport concerns.”