RestTemplate execute() method cannot send JSON Payload - spring

Question

In my application, I need to take data from another request and chain into a new one
I must use the exchange() method of RestTemplate because I have issue with jacksons lib and I cannot add/change the libs.
this is my code:
final RequestCallback requestCallback = new RequestCallback() {
#Override
public void doWithRequest(final ClientHttpRequest request) throws IOException {
request.getHeaders().add(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE);
// Add basic auth header
String auth = username + ":" + password;
byte[] encodedAuth = Base64Utils.encode(auth.getBytes(StandardCharsets.US_ASCII));
String authHeader = "Basic " + new String(encodedAuth);
request.getHeaders().add("Authorization", authHeader);
// Add Headers Request
Enumeration headerNamesReq = servletRequest.getHeaderNames();
while (headerNamesReq.hasMoreElements()) {
String headerName = (String) headerNamesReq.nextElement();
if (whiteListedHeaders.contains(headerName.toLowerCase())) {
String headerValue = servletRequest.getHeader(headerName);
request.getHeaders().add(headerName, headerValue);
}
}
request.getHeaders().forEach((name, value) -> {
log.info("RestExecutorMiddleware", "HEADERS ---\t" + name + ":" + value);
});
IOUtils.copy(new ByteArrayInputStream(payload.getBytes()), request.getBody());
}
};
// Factory for restTemplate
SimpleClientHttpRequestFactory requestFactory = new SimpleClientHttpRequestFactory();
requestFactory.setBufferRequestBody(false);
restTemplate.setRequestFactory(requestFactory);
ClientHttpResponse responsePost = restTemplate.execute(url, method, requestCallback, new ResponseFromHeadersExtractor());
But at the end, the endpoint cannot receive my JSON (receive data, but not JSON.)
Where I wrong?
Thanks

Answer 1

Very inaccuracy code. Make all steps one-to-one and it will work, you make optimization later ...
Basic Auth. Don't do unnecessary actions
var headers = new HttpHeaders();
headers.setBasicAuth(username, password);
That's all, Spring will take care of everything else - to apply Base64, add Basic: and set properly a header.
Set all required headers including headers.setContentType(MediaType.APPLICATION_JSON)
Get an entity/object which you need to send (set as a body) with a request.
Serialize your object. The most popular, proper and simple way is using fasterxml json framework, you can make serialization with mapper.writeBalueAsString(<your object>). If you really cannot use external libraries, HttpEntity should make it: var request = new HttpEntity<>(<object>, headers);
Make restTemplate request. In almost all cases more convenient methods are restTemplate.postForObject(), restTemplate.getForObject(), restTemplate.postForEntity(), etc.: restTemplate.postForObject(uri, request, ResponseObject.class)