How to mock the ResponseEntity<?> with generic type?

Question

I need to mock a service. i m getting null in ResponseEntity<?> resp while mocking the class.

Method which need to mock:

public List<Expression> getExpression(String expressView, Localdate date) {

    List<Expression> =new ArrayList<>();
    Map<String, Object> uri = new HashMap<>();
    UriComponenetsBuilder build = 
        UriComponentsBuilder.fromHttpUrl("someUrl" + "/" + expressView);
    build.queryParam(someParameter, someParameter);
    build.queryParam(someParameter, someParameter);
    build.queryParam(someParameter, someParameter);

    HttpHeaders header = new HttpHeaders();
    header.setContentType(MediaType.APPLICATION_JSON);
    RestClient client = new RestClient(
        build.build().encode.toUriString, HttpMethod.GET.Uri, header
    );

    ResponseEntity<?> resp = restC.SomeMethod(client);

    if (resp = !null) {
        //it goes to these line
    }

  }

In my mock method:

when(restC.SomeMethod(client)).thenReturn(resp);

So above method call a service get some data get the value of expressView and save as list. when i mocked the method when(restC.SomeMethod(client)).thenReturn(resp); it hit the URL but the value i m getting as response resp is null . So here i m getting the resp value as null. I checked the URL(someUrl) in postman its returning the value.

How to mock the ResponseEntity<?>?

Thanks.

Solution

First, create a ResponseEntity object:

HttpHeaders header = new HttpHeaders();
header.setContentType(MediaType.APPLICATION_JSON);

ResponseEntity<?> responseEntity = new ResponseEntity<>(
    "some response body",
    header, 
    HttpStatus.OK
);

Then build a mock to return the responseEntity object:

when(restC.SomeMethod(client)).thenReturn(responseEntity);

---

Point to pay attention:

Avoid to use ResponseEntity inside @Service class. You should use ResponseEntity in @RestController class.

And you can Inject your @Service class using @Autowired annotation, like:

@RestController
public class YourControllerClass {

    @Autowired
    private YourServiceClass yourServiceClass;

Or using constructor, like:

@RestController
public class YourControllerClass {

    private YourServiceClass yourServiceClass;

    public YourControllerClass(YourServiceClass yourServiceClass) {
        this.yourServiceClass= yourServiceClass;
    }

So:

@Service class will handle business or data objects and @RestController class will handle Response and Request objects. Thus we have Single Responsibility principle.

---

Some nice links:

• Spring MVC - Using RequestEntity and ResponseEntity
• How do I mock a REST template
• Building REST services with Spring
• Understanding the Single Responsibility Principle

Hope this helps!

Comments

[Juliano Macedo]

I improved my answer with suggestions, examples and some nice links ;) I hope this will help you.