微信支付，怎么获取prepay_id？

Question

Java写的，获取到的prepay_id 一直为空，不知道该怎么获取，这与设置API秘钥有关吗？

public static String getPayNo(String url, String xmlParam) {
DefaultHttpClient client = new DefaultHttpClient();
client.getParams().setParameter(ClientPNames.ALLOW_CIRCULAR_REDIRECTS,
true);
HttpPost httpost = HttpClientConnectionManager.getPostMethod(url);
String prepay_id = "";
try {
httpost.setEntity(new StringEntity(xmlParam, "UTF-8"));
HttpResponse response = httpclient.execute(httpost);
String jsonStr = EntityUtils
.toString(response.getEntity(), "UTF-8");

        System.out.println("--jsonStr--"+jsonStr);
        Map<String, Object> dataMap = new HashMap<String, Object>();

        if (jsonStr.indexOf("FAIL") != -1) {
            return prepay_id;
        }
        Map map = doXMLParse(jsonStr);
        String return_code = (String) map.get("return_code");
        prepay_id = (String) map.get("prepay_id");
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return prepay_id;
}

Answer 1

有没有签名，自己去做签名，然后给微信那边发送请求后返回prepay_id