将接口实现作为Spring @RequestBody参数传递

Question

I have the the following classes:

public class ItemController implements ApiController<Item> {
  @RequestMapping(value = "/", method = RequestMethod.POST)
  public Item create(@RequestBody final CreateItemRequest request) {
    // ...
  }
}

public interface ApiController<T> {
  T create(@RequestBody final ApiRequest request);
}


public class CreateItemRequest implements ApiRequest {
  // ...
}

public interface ApiRequest {
  // ...
}

I'm warned by Intellij that ItemController does not implement ApiController . My working assumption is that CreateItemRequest , as an implementation of ApiRequest , is a valid type for the signature of the create method as it's written above. However, Intellij insists that the type of the request parameter should be ApiRequest .

My goal here is to have a common interface for classes like CreateItemRequest to implement. That interface would be referred to in a generic-y sort of way within ApiController methods.

Obviously, I'm not a generics wizard, so what have I mixed up here?

edit: ThingRequest properly implements ApiRequest .

Answer 1

Update:

You can not narrow method parameters while implementing an interface! - The

You have an interface ApiController<T> with the method T create(final ApiRequest request) . This interface tells a client that he can invoke the method create with ANY!!! class that implements ApiRequest , therefore it is not allowed to have a implementation of ApiController that restrict the argument type of create to CreateItemRequest !!

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old answer:

You wrote:

public interface ApiController<T> {
  T create(@RequestBody final ApiRequest request);
}

and

public class ItemController implements ApiController<Item> {
  @RequestMapping(value = "/", method = RequestMethod.POST)
  public Thing create(@RequestBody final CreateItemRequest request) {
    // ...
  }
}

One problem is the method argument, the problem is the return type! Thing is not Item !

OK you told that this is an typo, so read the update above

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BTW: I strongly recommend to add the @Override annotation to methods that implement/override other methods