Java - Peticion Post mediante Java

<form action="<c:out value='${index_form.safetyCreateExpressToken}'/>" method="POST">

				<input type="hidden" name="ApiKey" value="<c:out value='${index_form.APIKey}'/>"/>

				<input type="hidden" name="RequestDateTime" value="<c:out value='${index_form.p_register_date}'/>"/>

				<input type="hidden" name="CurrencyCode" value="PEN"/>

				<input type="hidden" name="Amount" value="<c:out value='${index_form.formatamount}'/>"/>

				<input type="hidden" name="MerchantSalesID" value="<c:out value='${index_form.safetyMerchantID}'/>"/>

				<input type="hidden" name="ExpirationTime" value ="15" />

				<input type="hidden" name="TrackingCode" value="INTRALOT"/>

				<input type="hidden" name="Language" value="ES" />

				<input type="hidden" name="TransactionOkURL" value="<c:out value='${index_form.safetyTransactionOkURL}'/>" />

				<input type="hidden" name="TransactionErrorURL" value="<c:out value='${index_form.safetyTransactionErrorURL}'/>" />

				<input type="hidden" name="Signature" value="<c:out value='${index_form.cifrado}'/>" />

				<input type="hidden" name="ResponseFormat" value="CSV"/>

				<input type="submit"  class="button-update-user" style="margin-left: 250px;" value="Aceptar"/>

				<a class="button-update-user-cancel" style="margin-left: 10px;" href="#" onclick="cancel();">Cancelar</a>

</form>

public String getRespueta() throws IOException {

	String respuesta = "";

	 URL url = new URL("https://blabla.com/blabla");

	 	HttpsURLConnection conn = (HttpsURLConnection) url.openConnection();

	    conn.setDoOutput(true);

	    OutputStreamWriter wr = new OutputStreamWriter(

	    conn.getOutputStream()); -->EXACTAMENTE AQUI SE GENERA EL ERROR

//escribimos

wr.write(data);

//cerramos la conexión

  wr.close();

  //obtenemos el flujo de lectura

  BufferedReader rd = new BufferedReader(new InputStreamReader(conn.getInputStream()));

     String linea;

     //procesamos al salida

     while ((linea = rd.readLine()) != null) {

        respuesta+= linea;

     }

return respuesta;

}

String data="lo que sea que tengas que mandar"

StringRequestEntity requestEntity= new StringRequestEntity(data, "text/xml","UTF-8");

HttpClient client= new HttpClient();

			client.getState().setCredentials(new AuthScope(AuthScope.ANY_HOST, AuthScope.ANY_PORT, AuthScope.ANY_REALM), new UsernamePasswordCredentials("usuario", "password"));

method= new PostMethod(url);

method.setRequestHeader("Content-Type","text/xml; charset=UTF-8");

method.setRequestHeader("Content-Length", data.length()+"");

method.setRequestEntity(requestEntity);

int codigoRespuesta=client.executeMethod(method);//Se espera un 200

String resul=method.getResponseBodyAsString();	//Aca maneja la respuesta

			System.out.println(resul);

public String getRespueta() throws IOException {

	String respuesta = "";

//	System.setProperty("https.proxySet", "true");

	 System.setProperty("https.proxyHost","192.168.100.14");Solo si usan una ip proxy

	 System.setProperty("https.proxyPort","8080");Solo si usan una ip proxy

	 URL url = new URL("https://blablabla.com/blabla");

	 	HttpsURLConnection conn = (HttpsURLConnection) url.openConnection();

	    conn.setDoOutput(true);

	    OutputStreamWriter wr = new OutputStreamWriter(

	            conn.getOutputStream());

//escribimos

wr.write(data);

//cerramos la conexión

  wr.close();

  //obtenemos el flujo de lectura

  BufferedReader rd = new BufferedReader(new InputStreamReader(conn.getInputStream()));

     String linea;

     //procesamos al salida

     while ((linea = rd.readLine()) != null) {

        respuesta+= linea;

     }

return respuesta;

}