（Notice：以下所有经验也是我根据网上的经验整理的，如有侵权可以联系我删除，Wx:IT_Ezra，QQ 654303408。有问题讨论也可联系我，QQ同上。）

（Tips：我是第一次开发，一个刚毕业的java工程师，我觉得我并非天赋异禀，我能学会，相信聪敏的你，一定可以）

(PS:目前微信拥有无可撼动的人口基数，越来越多的项目开发是基于微信小程序，或者APP。但是支付方式无非两种，一种是支付宝，一种是微信支付。那么我们来了解一下微信支付。（首先去读5遍微信支付开发文档，地址https://pay.weixin.qq.com/wiki/doc/api/wxa/wxa_api.php?chapter=7_3&index=1），了解原理以及它的过程和参数列表。)

（PS：2019-03-27 代码已经更新。更加优化了。根据业内人士称，支付过程应该下沉到service层。代码目前更新了。回调目前没有下沉。可以加我QQ或者维信沟通，完善后会通知大家）

Controller类

 @RestController@RequestMapping("/pay")public class PayController {    @RequestMapping(value = "/wxPay", method = RequestMethod.POST)    public String wxPay(String openId, String orderNumber ,HttpServletRequest request) {        Object result = new Object();        try {        //获取自己的openId，可以找前端要       //  String openId = "xxx";         //订单号，自己的订单设计，最好用固定长度 20位等等。      //   String orderNumber = "xxxx";            //获取客户端的ip地址            String spbill_create_ip = getIpAddr(request);            //将支付业务下沉到service层  result = senseAgroOrderService.wxPay(spbill_create_ip, openId, orderNumber );         } catch (Exception e) {            e.printStackTrace();        }        return PayUtil.toJson(result);    }    //这里是支付回调接口，微信支付成功后会自动调用    @RequestMapping(value = "/wxNotify", method = RequestMethod.POST)    public void wxNotify(HttpServletRequest request, HttpServletResponse response) throws Exception {        BufferedReader br = new BufferedReader(new InputStreamReader(request.getInputStream()));        String line = null;        StringBuilder sb = new StringBuilder();        while ((line = br.readLine()) != null) {            sb.append(line);        }        br.close();        //sb为微信返回的xml        String notityXml = sb.toString();        String resXml = "";        Map map = PayUtil.doXMLParse(notityXml);        String returnCode = (String) map.get("return_code");        if ("SUCCESS".equals(returnCode)) {            //验证签名是否正确            Map<String, String> validParams = PayUtil.paraFilter(map);  //回调验签时需要去除sign和空值参数            String prestr = PayUtil.createLinkString(validParams);             //根据微信官网的介绍，此处不仅对回调的参数进行验签，还需要对返回的金额与系统订单的金额进行比对等            if (PayUtil.verify(prestr, (String) map.get("sign"), WechatConfig.key, "utf-8")) {                /**此处添加自己的业务逻辑代码start**/                                //注意要判断微信支付重复回调，支付成功后微信会重复的进行回调                                /**此处添加自己的业务逻辑代码end**/                //通知微信服务器已经支付成功                resXml = "<xml>" + "<return_code><![CDATA[SUCCESS]]></return_code>"                        + "<return_msg><![CDATA[OK]]></return_msg>" + "</xml> ";            }        } else {            resXml = "<xml>" + "<return_code><![CDATA[FAIL]]></return_code>"                    + "<return_msg><![CDATA[报文为空]]></return_msg>" + "</xml> ";        }        BufferedOutputStream out = new BufferedOutputStream(                response.getOutputStream());        out.write(resXml.getBytes());        out.flush();        out.close();    }    //获取IP    private String getIpAddr(HttpServletRequest request) {        String ip = request.getHeader("X-Forwarded-For");        if (StringUtils.isNotEmpty(ip) && !"unKnown".equalsIgnoreCase(ip)) {            //多次反向代理后会有多个ip值，第一个ip才是真实ip            int index = ip.indexOf(",");            if (index != -1) {                return ip.substring(0, index);            } else {                return ip;            }        }        ip = request.getHeader("X-Real-IP");        if (StringUtils.isNotEmpty(ip) && !"unKnown".equalsIgnoreCase(ip)) {            return ip;        }        return request.getRemoteAddr();    }}

Payservice层

@Service@Transactional(propagation = Propagation.REQUIRED, isolation = Isolation.DEFAULT)public class SenseAgroOrderService {public Map wxPay(String spbill_create_ip, String openId, String orderNumber) {Map<String, Object> payMap = new HashMap<String, Object>();//返回给小程序端需要的参数try {//生成的随机字符串String nonce_str = getRandomStringByLength(32);//商品名称//todoString body = "测试商品名称";//获取客户端的ip地址  BigDecimal ￥ = new BigDecimal(100.00);            int price = order.getAdjustPrice().multiply(￥).intValue();//组装参数，用户生成统一下单接口的签名logger.info("----------下单接口签名-------");Map<String, String> packageParams = new HashMap<>();packageParams.put("appid", WechatConfig.appid);packageParams.put("mch_id", WechatConfig.mch_id);packageParams.put("nonce_str", nonce_str);packageParams.put("body", body);packageParams.put("out_trade_no", orderNumber);//商户订单号,自己的订单IDpackageParams.put("total_fee", price + "");//支付金额，这边需要转成字符串类型，否则后面的签名会失败packageParams.put("spbill_create_ip", spbill_create_ip);packageParams.put("notify_url", WechatConfig.notify_url);//支付成功后的回调地址packageParams.put("trade_type", WechatConfig.TRADETYPE);//支付方式packageParams.put("openid", openId + "");//用户的openID，自己获取String prestr = PayUtil.createLinkString(packageParams); // 把数组所有元素，按照“参数=参数值”的模式用“&”字符拼接成字符串logger.info("----------prestr:" + prestr);logger.info("----------调用统一下单接口-------");//MD5运算生成签名，这里是第一次签名，用于调用统一下单接口String mysign = PayUtil.sign(prestr, WechatConfig.key, "utf-8").toUpperCase();logger.info("----------mysign:" + mysign);//拼接统一下单接口使用的xml数据，要将上一步生成的签名一起拼接进去String xml = "<xml>" + "<appid>" + WechatConfig.appid + "</appid>"+ "<attach>" + attach + "</attach>"+ "<body><![CDATA[" + body + "]]></body>"+ "<mch_id>" + WechatConfig.mch_id + "</mch_id>"+ "<nonce_str>" + nonce_str + "</nonce_str>"+ "<notify_url>" + WechatConfig.notify_url + "</notify_url>"+ "<openid>" + openId + "</openid>"+ "<out_trade_no>" + payOrderNumber + "</out_trade_no>"+ "<spbill_create_ip>" + spbill_create_ip + "</spbill_create_ip>"+ "<total_fee>" + price + "</total_fee>"//支付的金额，单位：分+ "<trade_type>" + WechatConfig.TRADETYPE + "</trade_type>"+ "<sign>" + mysign + "</sign>"+ "</xml>";//调用统一下单接口，并接受返回的结果String result = PayUtil.httpRequest(WechatConfig.pay_url, "POST", xml);logger.info("----------result:" + result);// 将解析结果存储在HashMap中Map map = PayUtil.doXMLParse(result);String return_code = (String) map.get("return_code");//返回状态码String result_code = (String) map.get("result_code");//返回状态码String err_code = (String) map.get("err_code");//返回状态码String err_code_des = (String) map.get("err_code_des");//返回状态码if (return_code.equals("SUCCESS") || return_code.equals(result_code)) {String prepay_id = (String) map.get("prepay_id");//返回的预付单信息payMap.put("nonceStr", nonce_str);payMap.put("package", "prepay_id=" + prepay_id);Long timeStamp = System.currentTimeMillis() / 1000;payMap.put("timeStamp", timeStamp + "");//这边要将返回的时间戳转化成字符串，不然小程序端调用wx.requestPayment方法会报签名错误//拼接签名需要的参数String stringSignTemp = "appId=" + WechatConfig.appid + "&nonceStr=" + nonce_str + "&package=prepay_id=" + prepay_id + "&signType=MD5&timeStamp=" + timeStamp;//再次签名，这个签名用于小程序端调用wx.requesetPayment方法String paySign = PayUtil.sign(stringSignTemp, WechatConfig.key, "utf-8").toUpperCase();logger.info("=======================第二次签名：", paySign + "============ ======");payMap.put("paySign", paySign);} else {logger.info("----------统一下单失败-------");return payMap;}//senseAgroOrderService.insert(payOperation);payMap.put("appid", WechatConfig.appid);} catch (Exception e) {e.printStackTrace();}return payMap;}    //获取随机字符串    private String getRandomStringByLength(int length) {        String base = "abcdefghijklmnopqrstuvwxyz0123456789";        Random random = new Random();        StringBuffer sb = new StringBuffer();        for (int i = 0; i < length; i++) {            int number = random.nextInt(base.length());            sb.append(base.charAt(number));        }        return sb.toString();    }}

上面代码用到了PayUtil和WechatConfig这两个类，一个是配置类，一个是工具类，代码如下：

public class PayUtil {    /**     * 签名字符串     *     * @param text          需要签名的字符串     * @param key           密钥     * @param input_charset 编码格式     * @return 签名结果     */    public static String sign(String text, String key, String input_charset) {        text = text + "&key=" + key;        return DigestUtils.md5Hex(getContentBytes(text, input_charset));    }    /**     * 签名字符串     *     * @param text          需要签名的字符串     * @param sign          签名结果     * @param key           密钥     * @param input_charset 编码格式     * @return 签名结果     */    public static boolean verify(String text, String sign, String key, String input_charset) {        text = text +"&key=" key;        String mysign = DigestUtils.md5Hex(getContentBytes(text, input_charset));        if (mysign.equals(sign)) {            return true;        } else {            return false;        }    }    /**     * @param content     * @param charset     * @return     * @throws java.security.SignatureException     * @throws UnsupportedEncodingException     */    public static byte[] getContentBytes(String content, String charset) {        if (charset == null || "".equals(charset)) {            return content.getBytes();        }        try {            return content.getBytes(charset);        } catch (UnsupportedEncodingException e) {            throw new RuntimeException("MD5签名过程中出现错误,指定的编码集不对,您目前指定的编码集是:" + charset);        }    }    private static boolean isValidChar(char ch) {        if ((ch >= '0' && ch <= '9') || (ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z'))            return true;        if ((ch >= 0x4e00 && ch <= 0x7fff) || (ch >= 0x8000 && ch <= 0x952f))            return true;// 简体中文汉字编码             return false;    }    /**     * 除去数组中的空值和签名参数     *     * @param sArray 签名参数组     * @return 去掉空值与签名参数后的新签名参数组     */    public static Map<String, String> paraFilter(Map<String, String> sArray) {        Map<String, String> result = new HashMap<String, String>();        if (sArray == null || sArray.size() <= 0) {            return result;        }        for (String key : sArray.keySet()) {            String value = sArray.get(key);            if (value == null || value.equals("") || key.equalsIgnoreCase("sign")                    || key.equalsIgnoreCase("sign_type")) {                continue;            }            result.put(key, value);        }        return result;    }    /**     * 把数组所有元素排序，并按照“参数=参数值”的模式用“&”字符拼接成字符串     *     * @param params 需要排序并参与字符拼接的参数组     * @return 拼接后字符串     */    public static String createLinkString(Map<String, String> params) {        List<String> keys = new ArrayList<>(params.keySet());        Collections.sort(keys);        String prestr = "";        for (int i = 0; i < keys.size(); i++) {            String key = keys.get(i);            String value = params.get(key);            if (i == keys.size() - 1) {// 拼接时，不包括最后一个&字符                     prestr = prestr + key + "=" + value;            } else {                prestr = prestr + key + "=" + value + "&";            }        }        return prestr;    }    /**     * @param requestUrl    请求地址     * @param requestMethod 请求方法     * @param outputStr     参数     */    public static String httpRequest(String requestUrl, String requestMethod, String outputStr) {        // 创建SSLContext             StringBuffer buffer = null;        try {            URL url = new URL(requestUrl);            HttpURLConnection conn = (HttpURLConnection) url.openConnection();            conn.setRequestMethod(requestMethod);            conn.setDoOutput(true);            conn.setDoInput(true);            conn.connect();            //往服务器端写内容                 if (null != outputStr) {                OutputStream os = conn.getOutputStream();                os.write(outputStr.getBytes("utf-8"));                os.close();            }            // 读取服务器端返回的内容                 InputStream is = conn.getInputStream();            InputStreamReader isr = new InputStreamReader(is, "utf-8");            BufferedReader br = new BufferedReader(isr);            buffer = new StringBuffer();            String line = null;            while ((line = br.readLine()) != null) {                buffer.append(line);            }            br.close();        } catch (Exception e) {            e.printStackTrace();        }        return buffer.toString();    }    public static String urlEncodeUTF8(String source) {        String result = source;        try {            result = java.net.URLEncoder.encode(source, "UTF-8");        } catch (UnsupportedEncodingException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        return result;    }    /**     * 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 org.jdom2.JDOMException     * @throws IOException     */    public static Map doXMLParse(String strxml) throws Exception {        if (null == strxml || "".equals(strxml)) {            return null;        }        Map m = new HashMap();        InputStream in = String2Inputstream(strxml);        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 = 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(getChildrenText(list));                }                sb.append(value);                sb.append("</" + name + ">");            }        }        return sb.toString();    }    public static InputStream String2Inputstream(String str) {        return new ByteArrayInputStream(str.getBytes());    }    /** * java对象转字符串 * @param <T> 泛型占位符 * @param obj T * @return String */public static <T> String toJson(T obj) {Gson gson = new GsonBuilder().setDateFormat("yyyy-MM-dd HH:mm:ss").enableComplexMapKeySerialization().create();return gson.toJson(obj);}}

WechatConfig

public class WechatConfig {    //小程序appid  开发者自己拥有的    public static final String appid = "";     //微信支付的商户id   开发者去问自己id的前端同事或者领导。    public static final String mch_id = "";    //微信支付的商户密钥  开发者问领导，去微信商户平台去申请（要下插件等等）    public static final String key = "";    //支付成功后的服务器回调url，这里填PayController里的回调函数地址    public static final String notify_url = "";    //签名方式，固定值    public static final String SIGNTYPE = "MD5";    //交易类型，小程序支付的固定值为JSAPI    public static final String TRADETYPE = "JSAPI";    //微信统一下单接口地址    public static final String pay_url = "https://api.mch.weixin.qq.com/pay/unifiedorder";}