Mocking RestTemplate while Testing

I am using restTemplate within a @services in spring boot. That service is making a rest call to an external api's. But during testing can I mock a restTemplate so that instead of calling a external api's it will return a certain file from the resources directory.

This is so far I am using, but not working..

 byte[] responseBody = readAllBytes(get("src", "test", "resources", "templates", "content", "xxx.txt"));
        Mockito.doReturn(ResponseEntity.ok(new String(responseBody, StandardCharsets.UTF_8)))
                .when(restTemplate).exchange("https://xxxxxxx.xxxx",
                                            HttpMethod.GET,
                                            entity,
                                            String.class);

Thank you..