本demo基于微信扫码支付退款（扫码支付暂时没放出demo下次有时间补上）

由于只是demo很多东西没有进行封装

官方地址：https://pay.weixin.qq.com/wiki/doc/api/wxa/wxa_api.php?chapter=9_4

需注意这两个参数我使用的是out_trade_no

image.png

请求XML示例

<xml>
   <appid>wx2421b1c4370ec43b</appid>
   <mch_id>10000100</mch_id>
   <nonce_str>6cefdb308e1e2e8aabd48cf79e546a02</nonce_str> 
   <out_refund_no>1415701182</out_refund_no>
   <out_trade_no>1415757673</out_trade_no>
   <refund_fee>1</refund_fee>
   <total_fee>1</total_fee>
   <transaction_id></transaction_id>
   <sign>FE56DD4AA85C0EECA82C35595A69E153</sign>
</xml>

逻辑代码

public static void main(String[] args) {
            try {
            //构建参数
            Map<String, String> dataMap = new HashMap<>();
            dataMap.put("appid","wx#################");
            dataMap.put("mch_id","137#############");
            //自行实现该随机串
            dataMap.put("nonce_str",Core.MD5("12344"));
            dataMap.put("out_trade_no","P190808170038402889c5318502");
            dataMap.put("out_refund_no","P190808170038402889c5318502");
            dataMap.put("total_fee","1");
            dataMap.put("refund_fee","1");
            dataMap.put("refund_desc","退款");
            //生成签名
            String sign = WXPayUtil.generateSignature(dataMap, "rv4###################");
            dataMap.put("sign", sign);
            //map数据转xml
            String xmlString = XMLBeanUtil.map2XmlString(dataMap);
            //发起退款
            doRefund("137####", "https://api.mch.weixin.qq.com/secapi/pay/refund", xmlString);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     *
     * @param mchId 商户ID
     * @param url 请求URL
     * @param data 退款参数
     * @return
     * @throws Exception
     */
    public static String doRefund(String mchId, String url, String data) throws Exception {
        /**
         * 注意PKCS12证书 是从微信商户平台-》账户设置-》 API安全 中下载的
         */
        KeyStore keyStore = KeyStore.getInstance("PKCS12");
        //这里自行实现我是使用数据库配置将证书上传到了服务器可以使用 FileInputStream读取本地文件
        ByteArrayInputStream inputStream = FileUtil.getInputStream("https://############################.p12");
        try {
            //这里写密码..默认是你的MCHID
            keyStore.load(inputStream, mchId.toCharArray());
        } finally {
            inputStream.close();
        } 
        SSLContext sslcontext = SSLContexts.custom()
                //这里也是写密码的
                .loadKeyMaterial(keyStore, mchId.toCharArray())
                .build(); 
        SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(
                sslcontext,
                SSLConnectionSocketFactory.getDefaultHostnameVerifier());
        CloseableHttpClient httpclient = HttpClients.custom()
                .setSSLSocketFactory(sslsf)
                .build();
        try {
            HttpPost httpost = new HttpPost(url);  
            httpost.setEntity(new StringEntity(data, "UTF-8"));
            CloseableHttpResponse response = httpclient.execute(httpost);
            try {
                HttpEntity entity = response.getEntity(); 
                //接受到返回信息
                String jsonStr = EntityUtils.toString(response.getEntity(), "UTF-8");
                EntityUtils.consume(entity);
                return jsonStr;
            } finally {
                response.close();
            }
        } finally {
            httpclient.close();
        }
    }

微信签名工具类

 /**
     * 生成签名 
     * @param data 待签名数据
     * @param key API密钥
     * @return 签名
     */
    public static String generateSignature(final Map<String, String> data, String key) throws Exception {
        return generateSignature(data, key, SignType.MD5);
    }

    /**
     * 生成签名. 注意，若含有sign_type字段，必须和signType参数保持一致。
     * @param data 待签名数据
     * @param key API密钥
     * @param signType 签名方式
     * @return 签名
     */
    public static String generateSignature(final Map<String, String> data, String key, SignType signType) throws Exception {
        Set<String> keySet = data.keySet();
        String[] keyArray = keySet.toArray(new String[keySet.size()]);
        Arrays.sort(keyArray);
        StringBuilder sb = new StringBuilder();
        for (String k : keyArray) {
            if (k.equals(WXPayConstants.FIELD_SIGN)) {
                continue;
            }
            if (data.get(k).trim().length() > 0) // 参数值为空，则不参与签名
                sb.append(k).append("=").append(data.get(k).trim()).append("&");
        }
        sb.append("key=").append(key);
        if (SignType.MD5.equals(signType)) {
            return MD5(sb.toString()).toUpperCase();
        }
        else if (SignType.HMACSHA256.equals(signType)) {
            return HMACSHA256(sb.toString(), key);
        }
        else {
            throw new Exception(String.format("Invalid sign_type: %s", signType));
        }
    }

map转XML工具类

    public static String map2XmlString(Map<String, String> map) {
        String xmlResult = "";

        StringBuffer sb = new StringBuffer();
        sb.append("<xml>");
        for (String key : map.keySet()) {
            String value = "<![CDATA[" + map.get(key) + "]]>";
            sb.append("<" + key + ">" + value + "</" + key + ">");
            System.out.println();
        }
        sb.append("</xml>");
        xmlResult = sb.toString();

        return xmlResult;
    }