jan jan - 1 year ago 1635
Java Question

Connection to trading API (Poloniex) with API key and secret

I am trying to connect to the Poloniex trading API, which is documented here: https://poloniex.com/support/api/.

Basically this describes everything one needs to know:

All calls to the trading API are sent via HTTP POST to https://poloniex.com/tradingApi and must contain the following headers:

Key - Your API key.

Sign - The query's POST data signed by your key's "secret" according to the HMAC-SHA512 method.

Additionally, all queries must include a "nonce" POST parameter. The nonce parameter is an integer which must always be greater than the previous nonce used.

But for some reason I get the error: Invalid command. I tried various commands but none did work.

public static String POLONIEX_SECRET_KEY = "my secret"; //KEY
public static String POLONIEX_API_KEY = "my key"; // TODO API KEY

public static void main(String[] args) {

try {
} catch (IOException e) {
// TODO Auto-generated catch block

public static final long generateNonce(){

Date d = new Date();
return d.getTime();

public static final void accessPoloniex() throws IOException{

String nonce = new BigDecimal(Polo2.generateNonce()).toString();

String connectionString = "https://poloniex.com/tradingApi";

String queryArgs = "command=returnBalances";

String hmac512 = hmac512Digest(queryArgs, POLONIEX_SECRET_KEY);

// Produce the output
ByteArrayOutputStream out = new ByteArrayOutputStream();
Writer writer = new OutputStreamWriter(out, "UTF-8");

CloseableHttpClient httpClient = HttpClients.createDefault();
HttpPost post = new HttpPost(connectionString);

post.setHeader("Key", POLONIEX_API_KEY);
post.setHeader("Sign", hmac512);

post.setEntity(new ByteArrayEntity(out.toByteArray()));
List<NameValuePair> params = new ArrayList<>();
params.add(new BasicNameValuePair("nonce", nonce));

CloseableHttpResponse response = null;
Scanner in = null;
post.setEntity(new UrlEncodedFormEntity(params));
response = httpClient.execute(post);
// System.out.println(response.getStatusLine());
HttpEntity entity = response.getEntity();
in = new Scanner(entity.getContent());
while (in.hasNext())

} finally


public static String hmac512Digest(String msg, String keyString) {

Mac shaMac;
try {
shaMac = Mac.getInstance("HmacSHA512");
SecretKeySpec keySpec = new SecretKeySpec(keyString.getBytes(), "HmacSHA512");

final byte[] macData = shaMac.doFinal(msg.getBytes());
return Hex.encodeHexString(macData); //again with try/catch for InvalidKeyException

} catch (Exception e1) {
// TODO Auto-generated catch block
return null;

Does anybody see any issue in that code?

jan jan
Answer Source

I figured it out:

I need to set "queryArgs" as "NameValuePair", then it works:

params.add(new BasicNameValuePair("command", "returnBalances"));
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