簡介：微信小程式支付這裡的坑還是有的，所以提醒各位在編寫的一定要注意！！！
1.首先呢，你需要準備openid，appid，還有申請微信支付後要設定一個32位的金鑰，需要先生成一個sign，得到prepay_id，然後再得到一個paySign，總之就是很墨跡，下面獻上我的controller

    //微信下單支付
    @ResponseBody
    @RequestMapping("doOrder")
    public void doOrder(HttpServletRequest request, HttpServletResponse response) throws IOException, JDOMException {
        request.setCharacterEncoding
 
("UTF-8");
        response.setCharacterEncoding("UTF-8");
        //得到openid
        String openid = request.getParameter("openid");
        int fee = 0;
        //得到小程式傳過來的價格，注意這裡的價格必須為整數，1代表1分，所以傳過來的值必須*100；
        if (null != request.getParameter("price")) {
            fee = Integer.parseInt(request.getParameter
 
("price").toString());

        }
        System.out.println(request.getParameter("price"));
        System.out.println(fee);
        //訂單編號
        String did = request.getParameter("did");
        //訂單標題
        String title = request.getParameter("title");
        //時間戳
        String times = System.currentTimeMillis
 
() + "";
        SortedMap<Object, Object> packageParams = new TreeMap<Object, Object>();
        packageParams.put("appid", "wxa**********2e2");
        packageParams.put("mch_id", "1486425722");
        packageParams.put("nonce_str", times);//時間戳
        packageParams.put("body", title);//支付主體
        packageParams.put("out_trade_no", did);//編號
        packageParams.put("total_fee", fee);//價格
        // packageParams.put("spbill_create_ip", getIp2(request));這裡之前加了ip，但是總是獲取sign失敗，原因不明，之後就註釋掉了
        packageParams.put("notify_url", base+"/notify");//支付返回地址，不用糾結這個東西，我就是隨便寫了一個介面，內容什麼都沒有
        packageParams.put("trade_type", "JSAPI");//這個api有，固定的
        packageParams.put("openid", openid);//openid
        //獲取sign
        String sign = PayCommonUtil.createSign("UTF-8", packageParams, "x********************************4");//最後這個是自己設定的32位金鑰
        packageParams.put("sign", sign);
        //轉成XML
        String requestXML = PayCommonUtil.getRequestXml(packageParams);
        System.out.println(requestXML);
        //得到含有prepay_id的XML
        String resXml = HttpUtil.postData("https://api.mch.weixin.qq.com/pay/unifiedorder", requestXML);
        System.out.println(resXml);
        //解析XML存入Map
        Map map = XMLUtil.doXMLParse(resXml);
        System.out.println(map);
        // String return_code = (String) map.get("return_code");
        //得到prepay_id
        String prepay_id = (String) map.get("prepay_id");
        SortedMap<Object, Object> packageP = new TreeMap<Object, Object>();
        packageP.put("appId", "wxa**********2e2");//！！！注意，這裡是appId,上面是appid，真懷疑寫這個東西的人。。。
        packageP.put("nonceStr", times);//時間戳
        packageP.put("package", "prepay_id=" + prepay_id);//必須把package寫成 "prepay_id="+prepay_id這種形式
        packageP.put("signType", "MD5");//paySign加密
        packageP.put("timeStamp", (System.currentTimeMillis() / 1000) + "");
        //得到paySign
        String paySign = PayCommonUtil.createSign("UTF-8", packageP, "x********************************4");
        packageP.put("paySign", paySign);
        //將packageP資料返回給小程式
        Gson gson = new Gson();
        String json = gson.toJson(packageP);
        PrintWriter pw = response.getWriter();
        System.out.println(json);
        pw.write(json);
        pw.close();

    }

2.下面是需要用到的工具類
（1）.生成sign以及得到sign後生成XML工具類PayCommonUtil

public class PayCommonUtil {
     /** 
     * 是否簽名正確,規則是:按引數名稱a-z排序,遇到空值的引數不參加簽名。 
     * @return boolean 
     */  
    public static boolean isTenpaySign(String characterEncoding, SortedMap<Object, Object> packageParams, String API_KEY) {  
        StringBuffer sb = new StringBuffer();  
        Set es = packageParams.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".equals(k) && null != v && !"".equals(v)) {  
                sb.append(k + "=" + v + "&");  
            }  
        }  

        sb.append("key=" + API_KEY);  

        //算出摘要  
        String mysign = MD5.MD5Encode(sb.toString(), characterEncoding).toLowerCase();  
        String tenpaySign = ((String)packageParams.get("sign")).toLowerCase();  

        //System.out.println(tenpaySign + "    " + mysign);  
        return tenpaySign.equals(mysign);  
    }  

    /** 
     * @author 
     * @Description：sign簽名 
     * @param characterEncoding 
     *            編碼格式 
     * @param parameters 
     *            請求引數 
     * @return 
     */  
    public static String createSign(String characterEncoding, SortedMap<Object, Object> packageParams, String API_KEY) {  
        StringBuffer sb = new StringBuffer();  
        Set es = packageParams.entrySet();  
        Iterator it = es.iterator();  
        while (it.hasNext()) {  
            Map.Entry entry = (Map.Entry) it.next();  
            String k = entry.getKey().toString();  
            String v = entry.getValue().toString();  
            if (null != v && !"".equals(v) && !"sign".equals(k) && !"key".equals(k)) {  
                sb.append(k + "=" + v + "&");  
            }  
        }  
        sb.append("key=" + API_KEY);  
        String sign = MD5.MD5Encode(sb.toString(), characterEncoding).toUpperCase();  
        return sign;  
    }  

    /** 
     * @author 
     * @Description：將請求引數轉換為xml格式的string 
     * @param parameters 
     *            請求引數 
     * @return 
     */  
    public static String getRequestXml(SortedMap<Object, Object> 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 = entry.getKey().toString();  
            String v = entry.getValue().toString();   
            if ("attach".equalsIgnoreCase(k) || "body".equalsIgnoreCase(k) || "sign".equalsIgnoreCase(k)) {  
                sb.append("<" + k + ">" + "<![CDATA[" + v + "]]></" + k + ">");  
            } else {  
                sb.append("<" + k + ">" + v + "</" + k + ">");  
            }  
        }  
        sb.append("</xml>");  
        return sb.toString();  
    }  

    /** 
     * 取出一個指定長度大小的隨機正整數. 
     *  
     * @param length 
     *            int 設定所取出隨機數的長度。length小於11 
     * @return int 返回生成的隨機數。 
     */  
    public static int buildRandom(int length) {  
        int num = 1;  
        double random = Math.random();  
        if (random < 0.1) {  
            random = random + 0.1;  
        }  
        for (int i = 0; i < length; i++) {  
            num = num * 10;  
        }  
        return (int) ((random * num));  
    }  

    /** 
     * 獲取當前時間 yyyyMMddHHmmss 
     *  
     * @return String 
     */  
    public static String getCurrTime() {  
        Date now = new Date();  
        SimpleDateFormat outFormat = new SimpleDateFormat("yyyyMMddHHmmss");  
        String s = outFormat.format(now);  
        return s;  
    }  
}

（2）.訪問官方介面得到含有prepay_id的XML工具類HttpUtil

public class HttpUtil {
     //private static final Log logger = Logs.get();  
        private final static int CONNECT_TIMEOUT = 5000; // in milliseconds  
        private final static String DEFAULT_ENCODING = "UTF-8";  

        public static String postData(String urlStr, String data){  
            return postData(urlStr, data, null);  
        }  

        public static String postData(String urlStr, String data, String contentType){  
            BufferedReader reader = null;  
            try {  
                URL url = new URL(urlStr);  
                URLConnection conn = url.openConnection();  
                conn.setDoOutput(true);  
                conn.setConnectTimeout(CONNECT_TIMEOUT);  
                conn.setReadTimeout(CONNECT_TIMEOUT);  
                if(contentType != null)  
                    conn.setRequestProperty("content-type", contentType);  
                OutputStreamWriter writer = new OutputStreamWriter(conn.getOutputStream(), DEFAULT_ENCODING);  
                if(data == null)  
                    data = "";  
                writer.write(data);   
                writer.flush();  
                writer.close();    

                reader = new BufferedReader(new InputStreamReader(conn.getInputStream(), DEFAULT_ENCODING));  
                StringBuilder sb = new StringBuilder();  
                String line = null;  
                while ((line = reader.readLine()) != null) {  
                    sb.append(line);  
                    sb.append("\r\n");  
                }  
                return sb.toString();  
            } catch (IOException e) {  
                //logger.error("Error connecting to " + urlStr + ": " + e.getMessage());  
            } finally {  
                try {  
                    if (reader != null)  
                        reader.close();  
                } catch (IOException e) {  
                }  
            }  
            return null;  
        }  
}

（3）.解析XML工具類

public class XMLUtil {
     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);  
            }  

            //關閉流  
            in.close();  

            return m;  
        }  

        /** 
         * 獲取子結點的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();  
        }  
}

（4）.MD5加密工具類

public class MD5 {
    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" };

}

3.小程式支付函式

gopay: function () {
    var that = this
    wx.request({
      url: app.baseurl + 'doOrder',
      data: {
        'openid': wx.getStorageSync('openids'),
        'title': that.data.title,
        'did': that.data.did,
        'price': that.data.price*100
      },
      method: 'POST',
      header: {
        "content-type": 'application/x-www-form-urlencoded'
      },
      success: function (res) {
        console.log(res.data)
        console.log(res.data.timeStamp)
        console.log(res.data.nonceStr)
        console.log(res.data.package)
        console.log(res.data.paySign)
        wx.requestPayment({
          timeStamp: res.data.timeStamp,
          nonceStr: res.data.nonceStr,
          package: res.data.package,
          signType: res.data.signType,
          paySign: res.data.paySign,
          success: function (res) {
            wx.request({
              url: app.baseurl+'updateState',
              data: {
                'did': that.data.did,
              },
              method: 'GET',
              success:function(res){
                console.log(res.data)
                if(res.data==1){
                  wx.redirectTo({
                    url: '../orderDetial/orderDetial?did=' + that.data.did,
                  })
                }
              }
            })
          },
          fail: function (res) {
            console.log(res)
          }
        })

      }
    })
  }

結束啦，小程式支付的java後臺就這些。