Could not write request: no suitable HttpMessageConverter found for request type

[theJava]

AuthenticateUser user = new AuthenticateUser(Credentials, Header);

String Stringifiedjson = new Gson().toJson(user);
Log.d("SpringAndroid", Stringifiedjson);

HttpHeaders requestHeaders = new HttpHeaders();
requestHeaders.setContentType(new MediaType("application", "json"));

HttpEntity < AuthenticateUser > requestEntity = new HttpEntity < AuthenticateUser > (user, requestHeaders);

RestTemplate restTemplate = new RestTemplate(true);
restTemplate.getMessageConverters().add(new MappingJacksonHttpMessageConverter());
restTemplate.getMessageConverters().add(new StringHttpMessageConverter());

final String url = getResources().getString(R.string.ProductionURL) + getResources().getString(R.string.AuthenticateUser);
Log.d(this.getClass().getName(), url);

try {
    ResponseEntity < String > responseEntity = restTemplate.exchange(url, HttpMethod.POST, requestEntity, String.class);
    result = responseEntity.getBody();
    Log.d("Result", result);
} catch (HttpClientErrorException e) {
    Log.d(Constants.HTTP_CLIENT_ERROR, e.getLocalizedMessage());
} catch (Exception e) {
    Log.d("It comes to here", e.getLocalizedMessage(), e);
}

StackTrace

10-23 20:37:59.245: D/It comes to here(3330): Could not write request: no suitable HttpMessageConverter found for request type [com.sample.transaction.AuthenticateUser] and content type [application/json]
10-23 20:37:59.245: D/It comes to here(3330): org.springframework.web.client.RestClientException: Could not write request: no suitable HttpMessageConverter found for request type [com.sample.transaction.AuthenticateUser] and content type [application/json]
10-23 20:37:59.245: D/It comes to here(3330): 	at org.springframework.web.client.RestTemplate$HttpEntityRequestCallback.doWithRequest(RestTemplate.java:632)
10-23 20:37:59.245: D/It comes to here(3330): 	at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:473)
10-23 20:37:59.245: D/It comes to here(3330): 	at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:438)
10-23 20:37:59.245: D/It comes to here(3330): 	at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:414)
10-23 20:37:59.245: D/It comes to here(3330): 	at com.sample.home.Trial$TrialAsyncTask.doInBackground(Trial.java:168)
10-23 20:37:59.245: D/It comes to here(3330): 	at com.sample.home.Trial$TrialAsyncTask.doInBackground(Trial.java:108)
10-23 20:37:59.245: D/It comes to here(3330): 	at android.os.AsyncTask$2.call(AsyncTask.java:287)
10-23 20:37:59.245: D/It comes to here(3330): 	at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
10-23 20:37:59.245: D/It comes to here(3330): 	at java.util.concurrent.FutureTask.run(FutureTask.java:137)
10-23 20:37:59.245: D/It comes to here(3330): 	at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
10-23 20:37:59.245: D/It comes to here(3330): 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
10-23 20:37:59.245: D/It comes to here(3330): 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
10-23 20:37:59.245: D/It comes to here(3330): 	at java.lang.Thread.run(Thread.java:856)

1. What is that i am missing here, i am getting this error. I did a lot of google on this from morning and could not reach to a solution.
2. How can is end Stringified JSONObject to my Service without using MappingJacksonHttpMessageConverter.

[Roy Clarkson]

Nothing is jumping out at me as being incorrect in your code. I would recommend using the MediaType.APPLICATION_JSON constant, but the result will be the same as your code. Can you confirm you are including the Jackson dependencies on your classpath? Also, what versions are you using? As an alternative, Spring for Android offers support for Gson through the GsonHttpMessageConverter.