how to post data in key/value pair? [duplicate]

Best would be using something like Spring and Jackson to create a JSON sending via a request, if you are not familiar with what you are trying to achieve:

This is just basic implementation

private final String uri = "yoururl.de/asdfasd";
private final HttpMethod httpMethod = HttpMethod.POST;
private final ContentType contentType = ContentType.json;

And EPO to transfer the Data

SendKeyValuePairsEPO implements Serializable{

    private static final long serialVersionUID = 5311348008314829094L;
    private final Integer startIndex;
    private final Integer size;
    private final Integer totalSize;

    private final List<KeyValuePairEPO> values;

    /**
     * Contructor
     *
     * @param startIndex start searching index
     * @param size       requested result size
     * @param totalSize  total size of available records
     * @param values      the key value pairs
     */
    public SendKeyValuePairsEPO(@JsonProperty("startIndex") final Integer startIndex,
                                  @JsonProperty("size") final Integer size,
                                  @JsonProperty("totalSize") final Integer totalSize,
                                  @JsonProperty("values") final List<KeyValuePairEPO> values) {
        this.startIndex = startIndex;
        this.size = size;
        this.totalSize = totalSize;
        this.values = values;
    }

and aswell a KeyValuePairEPO:

KeyValuePairEPO implements Serializable{

    private static final long serialVersionUID = 5311348008314829094L;
    private final String key;
    private final String value;
    private final String type; //maybe you need a type to tell what kind of value it is

...

And at last you will need to do something like:

/*package*/ <T> T sendRequest(Class<T> responseClass, Object requestEpo, String uri) {
    try {
        //Parse encapsulated COntent type to media type
        HttpHeaders headers = new HttpHeaders();
        MediaType requestContentType requestContentType = MediaType.APPLICATION_JSON;

        //Set content type and accept header to this type
        headers.setContentType(requestContentType);
        headers.setAccept(Collections.singletonList(requestContentType));
        //Parse the data object to a JSON
        String requestJSONAsString = "";
        if (request.getData() != null) {
            try {
                requestJSONAsString = RestObjectMapper.getInstance().writeValueAsString(requestEpo);
            } catch (JsonProcessingException ex) {
                throw new InternalServerErrorException(String.format("Error parsing: %s", requestEpo.getClass().getSimpleName()), ex);
            }
        }
        //Perform the send request
        return sendRequest(responseClass, uri, headers, httpMethod, requestJSONAsString);

    } finally {
        LOG.debug("Ended sendRequest");
    }
}

private <T> T sendRequest(final Class<T> responseClass, final String uri, final HttpHeaders httpHeaders, final HttpMethod httpMethod, String requestJSON) {
    try {
        LOG.debug(String.format("Start sendRequest with:%s %s %s %s", uri, httpHeaders, httpMethod, requestJSON));
        RestTemplate rest = new RestTemplate();
        ClientHttpRequestFactory restFactory = rest.getRequestFactory();
        if(restFactory instanceof SimpleClientHttpRequestFactory){
            ((SimpleClientHttpRequestFactory)restFactory).setReadTimeout(REQUEST_TIMEOUT);
            ((SimpleClientHttpRequestFactory)restFactory).setConnectTimeout(REQUEST_TIMEOUT);
        }

        HttpEntity<String> entity = new HttpEntity<>(requestJSON, httpHeaders);

        final ResponseEntity<String> response = rest.exchange(uri, httpMethod, entity, String.class);
        LOG.debug("Status:" + response.getStatusCode().toString());
        String returnedPayload = response.getBody();
        return RestObjectMapper.getInstance().readValue(returnedPayload, responseClass);
    } catch (HttpStatusCodeException ex) {
        LOG.error("HTTP Error in sendRequest: " + ex.getMessage());
        switch (ex.getStatusCode()) {
            case BAD_REQUEST:
                throw new BadRequestException(uri, ex);
            case NOT_FOUND:
                throw new NotFoundException(uri, ex);
            case FORBIDDEN:
                throw new ForbiddenException(uri, ex);
            case REQUEST_TIMEOUT:
                throw new RequestTimeoutException(ex, REQUEST_TIMEOUT);
            default:
                throw new InternalServerErrorException(ex);
        }
    } catch (Exception ex) {
        LOG.error("Error in sendRequest: " + ex.getMessage());
        throw new InternalServerErrorException(ex);
    } finally {
        LOG.debug("Ended sendRequest");
    }

}

where RestObjectMapper is:

public class RestObjectMapper extends ObjectMapper {
public static final String EMPTY_JSON = "{}";
private static final long serialVersionUID = 3924442982193452932L;

/**
 * Singleton Instance
 * Pattern: Initialization-on-demand holder idiom:
 * <ul>
 * <li>the class loader loads classes when they are first accessed (in this case Holder's only access is within the getInstance() method)</li>
 * <li>when a class is loaded, and before anyone can use it, all static initializers are guaranteed to be executed (that's when Holder's static block fires)</li>
 * <li>the class loader has its own synchronization built right in that make the above two points guaranteed to be threadsafe</li></ul>
 */
private static class INSTANCE_HOLDER {
    private static final RestObjectMapper INSTANCE = new RestObjectMapper();
}

private RestObjectMapper() {
    super();
    configure(SerializationFeature.WRITE_ENUMS_USING_TO_STRING, true);
    configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, true);
    configure(DeserializationFeature.READ_ENUMS_USING_TO_STRING, true);
    configure(DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_AS_NULL, true);
    configure(DeserializationFeature.UNWRAP_ROOT_VALUE, false);
    configure(DeserializationFeature.USE_BIG_DECIMAL_FOR_FLOATS, true);
    setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
}

/**
 * Gets the singleton Instance of the JSON Mapper
 *
 * @return the singleton instance
 */
public static RestObjectMapper getInstance() {
    return INSTANCE_HOLDER.INSTANCE;
}

By the way ResponseClass is another EPO the result (JSON) will be mapped to.