Accessing Poloniex HTTP API with Java -

i try connect poloniex.com api https://poloniex.com/support/api/ says:

(all calls trading api sent via http post https://poloniex.com/tradingapi , must contain following headers:

• key - api key.
• sign - query's post data signed key's "secret" according hmac-sha512 method.

additionally, queries must include "nonce" post parameter. nonce parameter integer must greater previous nonce used.)

but

{"error":"invalid api key\/secret pair."} 

my hmac512digest works fine, i've checked it.

there must wrong in code.

can please help?

   public class pol2 {      public static string poloniex_secret_key = "12345";      public static string poloniex_api_key = "abx";        public static void main(string[] args) {         try {             accesspoloniex();         } catch (ioexception e) {             e.printstacktrace();         }     }       public static final void accesspoloniex() throws ioexception {          final string nonce = string.valueof(system.currenttimemillis());          string connectionstring = "https://poloniex.com/tradingapi";          string queryargs = "command=returnbalances";          string hmac512 = hmac512digest(queryargs, poloniex_secret_key);          // produce output         bytearrayoutputstream out = new bytearrayoutputstream();         writer writer = new outputstreamwriter(out, "utf-8");         writer.append(queryargs);         writer.flush();          closeablehttpclient httpclient = httpclients.createdefault();         httppost post = new httppost(connectionstring);         post.addheader("key", poloniex_api_key); //or setheader?         post.addheader("sign", hmac512);  //or setheader?          post.setentity(new bytearrayentity(out.tobytearray()));         list<namevaluepair> params = new arraylist<>();          params.add(new basicnamevaluepair("command", "returnbalances"));         params.add(new basicnamevaluepair("nonce", nonce));          closeablehttpresponse response = null;         scanner in = null;         try {             post.setentity(new urlencodedformentity(params));             response = httpclient.execute(post);             httpentity entity = response.getentity();             in = new scanner(entity.getcontent());             while (in.hasnext()) {                 system.out.println(in.next());             }             entityutils.consume(entity);         } {             in.close();             response.close();         }     } } 

i've looked python example they've linked on page. nonce parameter must mac'ed along command , final mac appended in hex-encoded format:

string queryargs = "command=returnbalances&nonce=" + nonce; string hmac512 = hmac512digest(queryargs, poloniex_secret_key); 

---

also, following

bytearrayoutputstream out = new bytearrayoutputstream(); writer writer = new outputstreamwriter(out, "utf-8"); writer.append(queryargs); writer.flush(); //... post.setentity(new bytearrayentity(out.tobytearray())); 

can reduced

post.setentity(new bytearrayentity(queryargs.getbytes("utf-8")));