Dropwizard good practices - json

Question

I have seen in a lot of places that a resource class in a dropwizard project has methods for GET and POST. These methods then access data from the database using the DAO and return back a json
public class DropwizardResource {
private DropwizardDAO ddao;
public DropwizardResource (DropwizardDAO ddao) {
this.ddao = ddao;
}
#GET
#Timed
#UnitOfWork
public List<String> getAllResources() {
return ddao.findAll();
}
}
Is it advisable to have a resource initialized with other clients for some other service and then have the json returned by manual conversion?
public class DropwizardResource {
private NonDbClient client;
public DropwizardResource (NonDbClient client) {
this.client = client;
}
#GET
#Timed
#UnitOfWork
public List<String> getAllResources() {
return toJson(client.findAll());
}
}

Answer 1

First off, let's be clear: you can do whatever you like in a Dropwizard resource - there's nothing inherently special about them.
On your specific question on whether you can use "[a client] for some other service" (e.g. another Dropwizard service, or something completely separate), the answer is yes, that's perfectly fine. Note, however, if you're not using Hibernate to access a database within your resource method, you don't need the #UnitOfWork annotation (which is for declaring that a session & transaction should be managed for you when that method is called).
Finally, you ask whether it's okay to "then have the json returned by manual conversion". It's a little hard to answer that question without knowing what client you're thinking of using, and what it returns when you call its findAll method. I can think of a couple of possible scenarios:
You get deserialised plain old Java objects back from your client (regardless of how they were serialised in transit - JSON, XML, crazy proprietary binary protocol, whatever). In this case, you just need to transform these into whatever object you want to return from your Dropwizard resource method (a List<String> in the case of your example). From there, Jersey and Jackson will deal with serialising this to JSON for you and putting that in the response from your resource.
You get a string containing JSON back from your client. In this case, you'll need to manually deserialise the JSON to Java objects (using a Jackson ObjectMapper - you can grab one from the Dropwizard Environment in your application's run method). At that point you can transform then and return them as in the above case.
In either case, I can't think why you'd want to be serialising to JSON (as in your example). That'd give you a String (not a List<String>). Unless you're doing something pretty quirky, you probably don't want to be returning a JSON string from your Dropwizard resource - that will then serialise it as JSON again, and will then result in a string full of JSON being deserialised again at the other end!