Cannot deserialize value of type `...` from Array value (token `JsonToken.START_ARRAY`)

knard
October 2, 2024
128 views
1 vote
2 Answers

My issue is that I’m trying to get an API endpoint to display but keep running into an error. I’m a bit of a newbie and not at all sure how to construct my code to resolve the issue.

My Error

Error while extracting response for type [class com.jokeapi.jokeDemo.domain.jokeResponse] and content type [application/json;charset=utf-8]] with root cause com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type com.jokeapi.jokeDemo.domain.jokeResponse from Array value (token JsonToken.START_ARRAY)

I’m using Spring Boot and have been following a tutorial for connecting to API endpoints

In my spring boot class looks like this with setters and getters. This works fine for the other API endpoints that return objects in key value pairs

@Getter
@Setter
public class jokeResponse {
    private Long id;
    private String type;
    private String setup;
    private String punchline;
}

As an example I’m able to return the JSON endpoints for objects that are in my jokeResponse class:

{
id: 281,
type: "general",
setup: "When does a joke become a dad joke?",
punchline: "When it becomes apparent."
}

But here is my problem. In my implementation class i have the following with a return method for getForObjects pointing to the jokeResponse class for this endpoint that points to that array. Which is wrong because the class only points to the API endpoint for objects with key value pairs from above.

 @Override
public jokeResponse getTypesList() {
    RestTemplate restTemplate = new RestTemplate();
     return restTemplate.getForObject("https://official-joke-api.appspot.com/types", jokeResponse.class);
}

The JSON endpoint looks like this, an array of strings:

[
 "general",
 "knock-knock",
 "programming",
 "dad"
]

I need to construct the method so it pulls the array of strings vs the objects and I’m not sure how to construct that.

I’ve tried replacing the class with String[].class in the getForObjects method but that doesn’t resolve it.

Answers

Chosen as BEST ANSWER
- knard
- October 2, 2024 at 6:06 pm
- 0 votes
0
With a little trial and error I was able to resolve this by replaceing the class name in the method with the type.
```
 @Override
    public String getTypesList() {
        RestTemplate restTemplate = new RestTemplate();
        return restTemplate.getForObject("https://official-joke-api.appspot.com/types", String.class);
}
```

(Edit)

I think you are confusing the endpoints. The /types returns a String[] and the /random returns a Joke.

Here is a general setup that you can follow. I tested this out locally, and it works great.

application.properties

This property controls the base URL for the joke API.

joke.api.base-url=https://official-joke-api.appspot.com

Application

Ensure that a RestTemplate bean is created in the Application.

package org.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
public class Application {
  public static void main(String[] args) {
    SpringApplication.run(Application.class, args);
  }

  @Bean
  public RestTemplate restTemplate(RestTemplateBuilder builder) {
    return builder.build();
  }
}

ApiHelper

This encapsulates the URL and provides a simple fetchData method.

package org.example.api;

import java.net.URI;
import java.net.URISyntaxException;
import lombok.RequiredArgsConstructor;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
import org.springframework.web.client.RestTemplate;

@Component
@RequiredArgsConstructor  // Injects: restTemplate
public class ApiHelper {
  private final RestTemplate restTemplate;

  @Value("${joke.api.base-url}")
  private String baseUrl;

  public <T> T fetchData(String endpoint, Class<T> clazz) {
    try {
      URI uri = new URI(baseUrl).resolve(endpoint);
      return restTemplate.getForObject(uri, clazz);
    } catch (URISyntaxException e) {
      throw new RuntimeException("Invalid URI syntax: " + baseUrl + endpoint, e);
    }
  }
}

Joke

Here is what a slimmed-down Lombok class would look like.

package org.example.domain;

import lombok.Value;

@Value
public class Joke {
  String type;
  String setup;
  String punchline;
  int id;
}

JokeService

The service is responsible for using the API helper to fetch the data and marshal it into the appropriate type.

package org.example.service;

import lombok.RequiredArgsConstructor;
import org.example.api.ApiHelper;
import org.example.domain.Joke;
import org.springframework.stereotype.Service;

@Service
@RequiredArgsConstructor  // Injects: apiHelper
public class JokeService {
  private final ApiHelper apiHelper;

  public String[] getJokeTypes() {
    return apiHelper.fetchData("/types", String[].class);
  }

  public Joke getRandomJoke() {
    return apiHelper.fetchData("/jokes/random", Joke.class);
  }
}

Joke Controller

Finally, the controller uses the service to wrap the API response in an HTTP response of OK (200).

package org.example.web;

import lombok.RequiredArgsConstructor;
import org.example.domain.Joke;
import org.example.service.JokeService;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/api/jokes")
@RequiredArgsConstructor  // Injects: jokeService
public class JokeController {
  private final JokeService jokeService;

  @GetMapping("/types")
  public ResponseEntity<String[]> getJokeTypes() {
    String[] jokeTypes = jokeService.getJokeTypes();
    return ResponseEntity.ok(jokeTypes);
  }

  @GetMapping("/random")
  public ResponseEntity<Joke> getRandomJoke() {
    Joke joke = jokeService.getRandomJoke();
    return ResponseEntity.ok(joke);
  }
}

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Cannot deserialize value of type `…` from Array value (token `JsonToken.START_ARRAY`)