Integrating WeChat Native Pay into a Java Backend for Membership Upgrade

Introduction

Recently we needed to add a payment function to a website so that users can become members after paying, providing additional features and generating revenue.

WeChat Pay Integration Overview

Clarify Payment Flow

A typical native WeChat Pay membership upgrade includes: user obtains payment info, selects a type and generates a QR code, user scans and pays, WeChat notifies the server, and the server upgrades the user to a member.

Step 1: Prepare Merchant Information

Obtain merchant number (mch-id), AppID, merchant API certificate serial number (mch-serial-no), API v3 key, and merchant private key.

Merchant platform: https://pay.weixin.qq.com/index.php/core/home

Step 2: Write Configuration and Inject Config Class

Place configuration in application.yml:

wechat:
  pay-config:
    # Authentication type
    auth-type: WECHATPAY2-SHA256-RSA2048
    # Merchant ID
    mch-id: 1···7
    # AppID
    appid: wx·····a2
    # Merchant API certificate serial number
    mch-serial-no: 5··················6
    # API v3 key
    api-v3-key: J··············123
    # Notify URL
    notify-url: https://······/notify // can ignore for now
    # Merchant private key
    private-key: MIME····

Configuration class:

@Data
@Configuration
@ConfigurationProperties(prefix = "wechat.pay-config")
public class WeChatPayConfig {
    private String authType;
    private String mchId;
    private String mchSerialNo;
    private String privateKey;
    private String apiV3Key;
    private String appId;
    private String notifyUrl;
}

RSA auto‑certificate bean:

@Configuration
public class BeanConfig {
    @Autowired
    private WeChatPayConfig weChatPayConfig;

    /** Create a singleton RSAAutoCertificateConfig for WeChat API */
    @Bean
    public RSAAutoCertificateConfig rsaAutoCertificateConfig() {
        return new RSAAutoCertificateConfig.Builder()
                .merchantId(weChatPayConfig.getMchId())
                .privateKey(weChatPayConfig.getPrivateKey())
                .merchantSerialNumber(weChatPayConfig.getMchSerialNo())
                .apiV3Key(weChatPayConfig.getApiV3Key())
                .build();
    }
}

Inject the config where needed:

@Autowired
private WeChatPayConfig weChatPayConfig;

Step 3: Generate QR Code for Native Pay

Official API docs: https://pay.weixin.qq.com/docs/merchant/sdk-tools/sdk-tool.html

Java SDK repository: https://github.com/wechatpay-apiv3/wechatpay-java

Sample code to create a pre‑pay order and obtain the QR code URL:

package com.wechat.pay.java.service;

import com.wechat.pay.java.core.Config;
import com.wechat.pay.java.core.RSAAutoCertificateConfig;
import com.wechat.pay.java.service.payments.nativepay.NativePayService;
import com.wechat.pay.java.service.payments.nativepay.model.Amount;
import com.wechat.pay.java.service.payments.nativepay.model.PrepayRequest;
import com.wechat.pay.java.service.payments.nativepay.model.PrepayResponse;

/** Native payment example */
public class QuickStart {
    @Autowired
    private WeChatPayConfig weChatPayConfig;
    @Autowired
    private RSAAutoCertificateConfig certificateConfig;

    public static void main(String[] args) {
        // Build service
        NativePayService service = new NativePayService.Builder().config(certificateConfig).build();
        // Set request parameters
        PrepayRequest request = new PrepayRequest();
        Amount amount = new Amount();
        amount.setTotal(100);
        request.setAmount(amount);
        request.setAppid("wxa9d9651ae******");
        request.setMchid("190000****");
        request.setDescription("测试商品标题");
        request.setNotifyUrl("https://notify_url");
        request.setOutTradeNo("out_trade_no_001");
        // Call API
        PrepayResponse response = service.prepay(request);
        // Print QR code URL
        System.out.println(response.getCodeUrl());
    }
}

Step 4: Handle Payment Notification

WeChat posts the payment result to the notify‑url you configured. Example controller:

@PostMapping("/notify")
public Map
getNativeNotify(HttpServletRequest request) {
    String resultCode = payService.solveNotify(request);
    Map
resultMap = new HashMap<>();
    resultMap.put("code", resultCode);
    // Respond to WeChat to stop further callbacks
    return resultMap;
}

The callback URL must be HTTPS and publicly reachable.

Step 5: Front‑end Polling for Result

Two approaches exist: polling or server push (WebSocket/SSE). We choose polling with Redis cache and a Bloom filter to avoid cache penetration.

Sample polling endpoint:

@GetMapping("/{tradeNo}/result")
public R
getPayResult(@PathVariable String tradeNo) {
    // Bloom filter check omitted for brevity
    if ("1".equals(redisService.getValue(RedisConstants.ORDER_IS_DEAL + tradeNo))) {
        Order order = orderDao.getOrderByTradeNo(tradeNo);
        String vipExpiration = redisService.getValue(RedisConstants.USER_VIP + order.getUid());
        redisService.deleteValue(RedisConstants.ORDER_IS_DEAL + tradeNo);
        return R.success(vipExpiration, "支付已成功, 本用户vip截至");
    }
    return R.error(ResultCode.FAILED, "订单未完成或不存在");
}

During local development, expose the server with a tool like ngrok so that WeChat can reach the HTTPS callback endpoint.

Conclusion

The article walks through the complete backend implementation of WeChat native payment, from merchant configuration, SDK usage, QR code generation, notification handling, to front‑end result polling, and mentions practical tips such as using ngrok for local testing.