/**
  * 获取sign签名
  * 
  * @return
  */
 private String genPayReq() {

  // 获取参数的值
  PayReq request = new PayReq();
  request.appId = ConstantsMember.APP_ID;
  request.partnerId = ConstantsMember.MCHID;
  request.prepayId = mPrepayId;
  request.packageValue = "Sign=WXPay";
  request.nonceStr = DataUtil.getGuid();
  request.timeStamp = DataUtil.getTimeStamp();

  // 把参数的值传进去SortedMap集合里面
  SortedMap<Object, Object> parameters = new TreeMap<Object, Object>();
//  {appid=wx34df375d7dae8c90, noncestr=3BF34EF2CA4A462DB8D4EA48E785CDC3, 
//    package=Sign=WXPay, partnerid=1349967601, 
//    prepayid=wx2016070910354542c7155d4e0846850809, timestamp=1468031760}
  parameters.put("appid", request.appId);
  parameters.put("noncestr", request.nonceStr);
  parameters.put("package", request.packageValue);
  parameters.put("partnerid", request.partnerId);
  parameters.put("prepayid", request.prepayId);
  parameters.put("timestamp", request.timeStamp);

  String characterEncoding = "UTF-8";
  String mySign = createSign(characterEncoding, parameters);
  System.out.println("我的签名是：" + mySign);
  return mySign;
 }

 /**
  * 微信支付签名算法sign
  * 
  * @param characterEncoding
  * @param parameters
  * @return
  */
 public static String createSign(String characterEncoding,
   SortedMap<Object, Object> parameters) {

  StringBuffer sb = new StringBuffer();
  Set es = parameters.entrySet();// 所有参与传参的参数按照accsii排序（升序）
  Iterator it = es.iterator();
  while (it.hasNext()) {
   @SuppressWarnings("rawtypes")
   Map.Entry entry = (Map.Entry) it.next();
   String k = (String) entry.getKey();
   Object v = entry.getValue();
   if (null != v && !"".equals(v) && !"sign".equals(k)
     && !"key".equals(k)) {
    sb.append(k + "=" + v + "&");
   }
  }
  sb.append("key=" + ConstantsMember.KEY); //KEY是商户秘钥
  String sign = MD5Util.MD5Encode(sb.toString(), characterEncoding)
    .toUpperCase();
  return sign; // D3A5D13E7838E1D453F4F2EA526C4766
      // D3A5D13E7838E1D453F4F2EA526C4766
 }