resttemplate getForObject map responsetype

Question

Update 02/05/2018 (about 4 years later)...I tested this again as people have been upvoting my question/answer and Sotirios Delimanolis is correct that I should not have to write the code in my answer to make this work. I used basically the same RestTemplate/REST service setup as shown in my question with the REST service having a confirmed response content type of application/json and RestTemplate was able to process the response with no issues into a Map.

---

I'm invoking a rest service that returns JSON like this:

{
   "some.key" : "some value",
   "another.key" : "another value"
}

I would like to think that I can invoke this service with a java.util.Map as the response type but that's not working for me. I get this exception:

org.springframework.web.client.RestClientException: Could not extract response: no suitable HttpMessageConverter found for response type [interface java.util.Map]

Should I just specify String as the response type and convert the JSON to a Map?

Edit I

Here's my restTemplate call:

private Map<String, String> getBuildInfo(String buildUrl) {
    return restTemplate.getForObject(buildUrl, Map.class);
}

Here's how I'm setting up the restTemplate:

@PostConstruct
public void initialize() {
    List<ClientHttpRequestInterceptor> interceptors = new ArrayList<>();
    interceptors.add(new ClientHttpRequestInterceptor() {
        @Override
        public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {
            HttpRequestWrapper requestWrapper = new HttpRequestWrapper(request);
            requestWrapper.getHeaders().setAccept(Arrays.asList(MediaType.APPLICATION_JSON));
            return execution.execute(requestWrapper, body);
        }
    });
    restTemplate.setInterceptors(interceptors);
}

Edit II

Full error message:

org.springframework.web.client.RestClientException: Could not extract response: no suitable HttpMessageConverter found for response type [interface java.util.Map] and content type [application/octet-stream]
    at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:108) ~[spring-web-4.0.3.RELEASE.jar:4.0.3.RELEASE]
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:549) ~[spring-web-4.0.3.RELEASE.jar:4.0.3.RELEASE]
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:502) ~[spring-web-4.0.3.RELEASE.jar:4.0.3.RELEASE]
    at org.springframework.web.client.RestTemplate.getForObject(RestTemplate.java:239) ~[spring-web-4.0.3.RELEASE.jar:4.0.3.RELEASE]
    at idexx.ordering.services.AwsServersServiceImpl.getBuildInfo(AwsServersServiceImpl.java:96) ~[classes/:na]

Answer 1

RestTemplate has a method named exchange that takes an instance of ParameterizedTypeReference as parameter.

To make a GET request that returns a java.util.Map, just create an instance of an anonym class that inherits from ParameterizedTypeReference.

ParameterizedTypeReference<HashMap<String, String>> responseType = 
               new ParameterizedTypeReference<HashMap<String, String>>() {};

You can then invoke the exchange method:

RequestEntity<Void> request = RequestEntity.get(URI("http://example.com/foo"))
                 .accept(MediaType.APPLICATION_JSON).build()
Map<String, String> jsonDictionary = restTemplate.exchange(request, responseType)