Mock external server during integration testing with Spring

I have a Spring web server that on a request makes an external call to some third-party web API (e.g. retreive Facebook oauth token). After getting data from this call it computes a response:

@RestController
public class HelloController {
    @RequestMapping("/hello_to_facebook")
    public String hello_to_facebook() {
        // Ask facebook about something
        HttpGet httpget = new HttpGet(buildURI("https", "graph.facebook.com", "/oauth/access_token"));
        String response = httpClient.execute(httpget).getEntity().toString();
        // .. Do something with a response
        return response;
    }
}

I'm writing an integration test that checks that hitting url on my server leads to some expected result. However I want to mock the external server locally so that I don't even need internet access to test all this. What is the best way to do this?

I'm a novice in spring, this is what I have so far.

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = Application.class)
@WebAppConfiguration
@IntegrationTest({})
public class TestHelloControllerIT {        
    @Test
    public void getHelloToFacebook() throws Exception {
        String url = new URL("http://localhost:8080/hello_to_facebook").toString();
        //Somehow setup facebook server mock ...
        //FaceBookServerMock facebookMock = ...

        RestTemplate template = new TestRestTemplate();
        ResponseEntity<String> response = template.getForEntity(url, String.class);
        assertThat(response.getBody(), equalTo("..."));

        //Assert that facebook mock got called
        //facebookMock.verify();
    }
}

The actual real set up is more complicated - I'm making Facebook oauth login and all that logic is not in the controller but in various Spring Security objects. However I suspect that testing code is supposed to be the same since I'm just hitting urls and expect a response, isn't it?