RestTemplate.postForObject()
private String postForObject(String requestUrl, String requestContent) {
HttpHeaders httpHeaders = new HttpHeaders();
httpHeaders.add("Content-Type", "application/json");
HttpEntity<String> request = new HttpEntity<>(requestContent, httpHeaders);
RestTemplate restTemplate = new RestTemplate();
String responseContent = restTemplate.postForObject(requestUrl, request, String.class);
return responseContent;
}