How ti pas a Header app in Java with RestTemplate

How ti pas a Header app in Java with RestTemplate

i try to pass the Header Parameter which works in SOAPUI in my Java Implementation with ResTemplate here my tries

private String cellWebService(String url, String requestBody, HttpMethod method, String sessiionID ) {
    String responseBody = "";
    try {
        RestTemplate restTemplate = new RestTemplate();
        List<HttpMessageConverter<?>> messageConverters = new ArrayList<HttpMessageConverter<?>>();
        messageConverters.add(new StringHttpMessageConverter());
        restTemplate.setMessageConverters(messageConverters);
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_XML);
        if (StringUtils.isNotEmpty(sessiionID) ) {
            //headers.
            headers.add("ClientSessionId",sessiionID);
        }
        Map<String, String> uriVariables = new HashMap<String, String>();
        if (StringUtils.isNotEmpty(sessiionID) ) {
            uriVariables.put("ClientSessionId", sessiionID);
        }
        URI expanded = restTemplate.getUriTemplateHandler().expand(url, uriVariables);
        HttpEntity<String> restRequest = new HttpEntity<String>(requestBody, headers);
        RequestCallback requestCallback = restTemplate.httpEntityCallback(restRequest, String.class);
        ResponseExtractor<ResponseEntity<String>> responseExtractor = restTemplate.responseEntityExtractor(String.class);
        //Object obj = null;
        //final ResponseEntity<String> response = restTemplate.exchange(url, method, restRequest, String.class,obj);
        final ResponseEntity<String> response = restTemplate.execute(url, method, requestCallback, responseExtractor,uriVariables);
        //final ResponseEntity<String> response = restTemplate.execute(expanded, method, requestCallback, responseExtractor);
        HttpStatus status = response.getStatusCode();
        boolean success = status.is2xxSuccessful();
        if (success) {
            if (response.hasBody()) {
                responseBody = response.getBody();
            }
        }
    } catch (Exception e) {
        reporter.debug(getClass(), e.toString());
    }
    return responseBody;
}

does somebody knows how i must do this