How to mock an API that returns a JSON string in Spring Boot

I am a beginner in trying to mock an external API in Spring Boot.

Here is the API:
https://jsonplaceholder.typicode.com/posts

It returns a JSON string like this:

[
  {
    "userId": 1,
    "id": 1,
    "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
    "body": "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto"
  },
...

I've tried the following code:

    @Service
    public class BlogPostService {
        @Autowired
        private RestTemplate restTemplate;

        public String getAllBlogPosts() {
            ResponseEntity resp = restTemplate.getForEntity("http://localhost:8080/posts", String.class);

            return resp.getStatusCode() == HttpStatus.OK ? resp.getBody() : null;
        }

    }

But there is an error in the IDE at resp.getBody() which says:

> Type mismatch: cannot convert from Object to String

Here is my BlogPost code:

public class BlogPost {
    private int userId;
    private String title;
    private String body;

    public BlogPost() {
    }

    public BlogPost(int userId, String title, String body) {
        this.title = title;
        this.body = body;
    }
//...getters & setters

How can I fix this? Hopefully without the use of yet another tool. This is just a simple proof-of-concept application, so I do not want to use JUnit or Mockito for testing.

The API https://jsonplaceholder.typicode.com/posts returns an array of JSON objects. You will need to reflect this in your request's desired response type:

public String getAllBlogPosts() {
    ResponseEntity resp = restTemplate.getForEntity("http://localhost:8080/posts", BlogPost[].class);

    return resp.getStatusCode() == HttpStatus.OK ? resp.getBody() : null;
}

Notice the [] in BlogPost[].class.

Then, you are getting a Type mismatch: cannot convert from Object to String since ResponseBody.getBody() returns a generic type T, which is BlogPost[], but your method signature returns a String.

If all you want is the JSON string, then you can just do this:

public String getAllBlogPosts() {
    ResponseEntity resp = restTemplate.getForEntity("http://localhost:8080/posts", String.class);

    return resp.getStatusCode() == HttpStatus.OK ? resp.getBody() : null;
}

Otherwise, if you want the actual POJO array then do this:

public BlogPost[] getAllBlogPosts() {
    ResponseEntity resp = restTemplate.getForEntity("http://localhost:8080/posts", BlogPost[].class);

    return resp.getStatusCode() == HttpStatus.OK ? resp.getBody() : null;
}