微信APP支付（Java后台生成签名具体步骤）

public class PayCommonUtil {

    //定义签名，微信根据参数字段的ASCII码值进行排序 加密签名,故使用SortMap进行参数排序
    public static String createSign(String characterEncoding,SortedMap<String,String> parameters){
        StringBuffer sb = new StringBuffer();
        Set es = parameters.entrySet();
        Iterator it = es.iterator();
        while(it.hasNext()) {
            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=" + ConstantUtil.PARTNER_KEY);//最后加密时添加商户密钥，由于key值放在最后，所以不用添加到SortMap里面去，单独处理，编码方式采用UTF-8
        String sign = MD5Util.MD5Encode(sb.toString(), characterEncoding).toUpperCase();
        return sign;
    }

//将封装好的参数转换成Xml格式类型的字符串

    public static String getRequestXml(SortedMap<String,String> parameters){
        StringBuffer sb = new StringBuffer();
        sb.append("<xml>");
        Set es = parameters.entrySet();
        Iterator it = es.iterator();
        while(it.hasNext()) {
            Map.Entry entry = (Map.Entry)it.next();
            String k = (String)entry.getKey();
            String v = (String)entry.getValue();
            if("sign".equalsIgnoreCase(k)){

            }
            else if ("attach".equalsIgnoreCase(k)||"body".equalsIgnoreCase(k)) {
                sb.append("<"+k+">"+"<![CDATA["+v+"]]></"+k+">");
            }
            else {
                sb.append("<"+k+">"+v+"</"+k+">");
            }
        }
        sb.append("<"+"sign"+">"+"<![CDATA["+parameters.get("sign")+"]]></"+"sign"+">");
        sb.append("</xml>");
        return sb.toString();
    }
}

//微信Md5加密工具

public class MD5Util {

   private static String byteArrayToHexString(byte b[]) {
      StringBuffer resultSb = new StringBuffer();
      for (int i = 0; i < b.length; i++)
         resultSb.append(byteToHexString(b[i]));

      return resultSb.toString();
   }

   private static String byteToHexString(byte b) {
      int n = b;
      if (n < 0)
         n += 256;
      int d1 = n / 16;
      int d2 = n % 16;
      return hexDigits[d1] + hexDigits[d2];
   }

   public static String MD5Encode(String origin, String charsetname) {
      String resultString = null;
      try {
         resultString = new String(origin);
         MessageDigest md = MessageDigest.getInstance("MD5");
         if (charsetname == null || "".equals(charsetname))
            resultString = byteArrayToHexString(md.digest(resultString
                  .getBytes()));
         else
            resultString = byteArrayToHexString(md.digest(resultString
                  .getBytes(charsetname)));
      } catch (Exception exception) {
      }
      return resultString;
   }

   private static final String hexDigits[] = { "0", "1", "2", "3", "4", "5",
         "6", "7", "8", "9", "a", "b", "c", "d", "e", "f" };

}

//微信返回的结果为Xml格式的字符串，XmlUtil主要用于解析结果

public class XMLUtil {

   /**
    * 解析xml,返回第一级元素键值对。如果第一级元素有子节点，则此节点的值是子节点的xml数据。
    * @param strxml
    * @return
    * @throws JDOMException
    * @throws IOException
    */
   public static Map doXMLParse(String strxml) throws JDOMException, IOException {
      strxml = strxml.replaceFirst("encoding=".*"", "encoding="UTF-8"");

      if(null == strxml || "".equals(strxml)) {
         return null;
      }

      Map m = new HashMap();

      InputStream in = new ByteArrayInputStream(strxml.getBytes("UTF-8"));
      SAXBuilder builder = new SAXBuilder();
      Document doc = builder.build(in);
      Element root = doc.getRootElement();
      List list = root.getChildren();
      Iterator it = list.iterator();
      while(it.hasNext()) {
         Element e = (Element) it.next();
         String k = e.getName();
         String v = "";
         List children = e.getChildren();
         if(children.isEmpty()) {
            v = e.getTextNormalize();
         } else {
            v = XMLUtil.getChildrenText(children);
         }

         m.put(k, v);
      }

      //关闭流
      in.close();

      return m;
   }

   /**
    * 获取子结点的xml
    * @param children
    * @return String
    */
   public static String getChildrenText(List children) {
      StringBuffer sb = new StringBuffer();
      if(!children.isEmpty()) {
         Iterator it = children.iterator();
         while(it.hasNext()) {
            Element e = (Element) it.next();
            String name = e.getName();
            String value = e.getTextNormalize();
            List list = e.getChildren();
            sb.append("<" + name + ">");
            if(!list.isEmpty()) {
               sb.append(XMLUtil.getChildrenText(list));
            }
            sb.append(value);
            sb.append("</" + name + ">");
         }
      }

      return sb.toString();
   }

   /**
    * 获取xml编码字符集
    * @param strxml
    * @return
    * @throws IOException
    * @throws JDOMException
    */
   public static String getXMLEncoding(String strxml) throws JDOMException, IOException {
      InputStream in = HttpClientUtil.String2Inputstream(strxml);
      SAXBuilder builder = new SAXBuilder();
      Document doc = builder.build(in);
      in.close();
      return (String)doc.getProperty("encoding");
   }
}

//发送https

public class CommonUtil {
    private static Logger log = LoggerFactory.getLogger(CommonUtil.class);
    /**
     * 发送https请求
     * @param requestUrl 请求地址
     * @param requestMethod 请求方式（GET、POST）
     * @param outputStr 提交的数据
     * @return 返回微信服务器响应的信息
     */
    public static String httpsRequest(String requestUrl, String requestMethod, String outputStr) {
        try {
            // 创建SSLContext对象，并使用我们指定的信任管理器初始化
            MyX509TrustManager[] tm = { new MyX509TrustManager() };
            SSLContext sslContext = SSLContext.getInstance("SSL", "SunJSSE");
            sslContext.init(null, tm, new java.security.SecureRandom());
            // 从上述SSLContext对象中得到SSLSocketFactory对象
            SSLSocketFactory ssf = sslContext.getSocketFactory();
            URL url = new URL(requestUrl);
            HttpsURLConnection conn = (HttpsURLConnection) url.openConnection();
            conn.setSSLSocketFactory(ssf);
            conn.setDoOutput(true);
            conn.setDoInput(true);
            conn.setUseCaches(false);
            // 设置请求方式（GET/POST）
            conn.setRequestMethod(requestMethod);
            conn.setRequestProperty("content-type", "application/x-www-form-urlencoded");
            // 当outputStr不为null时向输出流写数据
            if (null != outputStr) {
                OutputStream outputStream = conn.getOutputStream();
                // 注意编码格式
                outputStream.write(outputStr.getBytes("UTF-8"));
                outputStream.close();
            }
            // 从输入流读取返回内容
            InputStream inputStream = conn.getInputStream();
            InputStreamReader inputStreamReader = new InputStreamReader(inputStream, "utf-8");
            BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
            String str = null;
            StringBuffer buffer = new StringBuffer();
            while ((str = bufferedReader.readLine()) != null) {
                buffer.append(str);
            }
            // 释放资源
            bufferedReader.close();
            inputStreamReader.close();
            inputStream.close();
            inputStream = null;
            conn.disconnect();
            return buffer.toString();
        } catch (ConnectException ce) {
            log.error("连接超时：{}", ce);
        } catch (Exception e) {
            log.error("https请求异常：{}", e);
        }
        return null;
    }

    /**
     * 获取接口访问凭证
     *
     * @param appid 凭证
     * @param appsecret 密钥
     * @return
     *//*
    public static Token getToken(String appid, String appsecret) {
        Token token = null;
        String requestUrl = ConfigUtil.TOKEN_URL.replace("APPID", appid).replace("APPSECRET", appsecret);
        // 发起GET请求获取凭证
        JSONObject jsonObject = JSONObject.fromObject(httpsRequest(requestUrl, "GET", null));

        if (null != jsonObject) {
            try {
                token = new Token();
                token.setAccessToken(jsonObject.getString("access_token"));
                token.setExpiresIn(jsonObject.getInt("expires_in"));
            } catch (JSONException e) {
                token = null;
                // 获取token失败
                log.error("获取token失败 errcode:{} errmsg:{}", jsonObject.getInt("errcode"), jsonObject.getString("errmsg"));
            }
        }
        return token;
    }
    public static String urlEncodeUTF8(String source){
        String result = source;
        try {
            result = java.net.URLEncoder.encode(source,"utf-8");
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return result;
    }*/
}

重点：封装参数调用统一下单接口，生成prepay_id(预支付订单Id)

/**
 * 微信支付
 * @param orderId 订单编号
 * @param actualPay 实际支付金额
 * @return 
 */
private String generateOrderInfoByWeiXinPay(String orderId, float actualPay,HttpServletRequest request,HttpServletResponse response) throws Exception{
   String notify_url = propertiesService.WEI_XIN_NOTIFY_URL;//回调地址
   String uuid = IdGen.uuid();
   System.out.print("uuid" + uuid);
   SortedMap<String, String> signParams = new TreeMap<String, String>();
   signParams.put("appid", ConstantUtil.APP_ID);//app_id
   signParams.put("body","测试");//商品参数信息
   signParams.put("mch_id", ConstantUtil.PARTNER);//微信商户账号
   signParams.put("nonce_str", uuid);//32位不重复的编号
   signParams.put("notify_url", notify_url);//回调页面
   signParams.put("out_trade_no", orderId);//订单编号
   signParams.put("spbill_create_ip",request.getRemoteAddr() );//请求的实际ip地址
   signParams.put("total_fee","1");//支付金额 单位为分
   signParams.put("trade_type", "APP");付款类型为APP
   String sign = PayCommonUtil.createSign("UTF-8", signParams);//生成签名
   signParams.put("sign", sign);
   signParams.remove("key");//调用统一下单无需key（商户应用密钥）
   String requestXml = PayCommonUtil.getRequestXml(signParams);//生成Xml格式的字符串
   String result = CommonUtil.httpsRequest   (ConstantUtil.UNIFIED_ORDER_URL, "POST", requestXml);//以post请求的方式调用统一下单接口

（注：ConstantUtil.UNIFIED_ORDER_URL=https://api.mch.weixin.qq.com/pay/unifiedorder;

）

返回的result成功结果取出prepay_id：

Map map = XMLUtil.doXMLParse(result);
String return_code=(String) map.get("return_code");
String prepay_id =null;
String returnSign=null;
String returnNonce_str=null;
if (return_code.contains("SUCCESS")){
   prepay_id=(String) map.get("prepay_id");//获取到prepay_id
}
StringBuffer weiXinVo=new StringBuffer();
long currentTimeMillis = System.currentTimeMillis();//生成时间戳
long second = currentTimeMillis / 1000L;（转换成秒）
String seconds = String.valueOf(second).substring(0, 10);（截取前10位）
SortedMap<String, String> signParam = new TreeMap<String, String>();
signParam.put("appid", ConstantUtil.APP_ID);//app_id
signParam.put("partnerid", ConstantUtil.PARTNER);//微信商户账号
signParam.put("prepayid", prepay_id);//预付订单id
signParam.put("package", "Sign=WXPay");//默认sign=WXPay
signParam.put("noncestr", uuid);//自定义不重复的长度不长于32位
signParam.put("timestamp",seconds);//北京时间时间戳
String signAgain = PayCommonUtil.createSign("UTF-8", signParam);//再次生成签名
signParams.put("sign", signAgain);
weiXinVo.append("appid=").append(ConstantUtil.APP_ID).append("&partnerid=").append(ConstantUtil.PARTNER).append("&prepayid=").append(prepay_id).append("&package=Sign=WXPay").append("&noncestr=").append(uuid).append("&timestamp=").append(seconds).append("&sign=").append(signAgain);//拼接参数返回给移动端
return weiXinVo.toString();

（注：感谢IOS团队的联调支持）