1. User agrees to authorize and get code

String redirecturi = HttpUtil.urlEnCode(domain + aliPay + QRCodeUrl);
SysPayChannel channel = payChannelService.selectByChannelType(PayTypeConstant.Alipay);
MyAliPayConfig aliPayConfig = new MyAliPayConfig();
aliPayConfig.setAppId(channel.getAppid());
// Authorization Page Address
String requestUrl = aliPayConfig.getAuthgateway();
requestUrl = requestUrl.replace("APPID", aliPayConfig.getAppId()).replace("SCOPE", aliPayConfig.getScope()).replace("REDIRECT_URI", redirecturi);
// Redirect to authorization page
response.sendRedirect(requestUrl);

2. Obtain openid by code

request.setCharacterEncoding("utf-8");
response.setCharacterEncoding("utf-8");
//After the user agrees to authorize, the code can be obtained.
String code = request.getParameter("auth_code");
String aliuserid = "";
if (!redisService.exists(code)){
	//User agrees to authorize
	if (!code.equals("")) {
		SysPayChannel channel = payChannelService.selectByChannelType(PayTypeConstant.Alipay);
		MyAliPayConfig aliPayConfig = new MyAliPayConfig();
		aliPayConfig.setAppId(channel.getAppid());
		String certsrc = channel.getPayCertUrl();
		Properties propertiesFile = PropertiesUtils.getPropertiesFile(certsrc);
		if (propertiesFile != null) {
			aliPayConfig.setPayeeAccount(propertiesFile.getProperty("ALI_PAYEE_ACCOUNT"));
			aliPayConfig.setAppId(propertiesFile.getProperty("ALI_APP_ID"));
			aliPayConfig.setAliPayPublicKey(propertiesFile.getProperty("ALI_ALIPAY_PUBLIC_KEY"));
			aliPayConfig.setAppPayPublicKey(propertiesFile.getProperty("ALI_APP_PAY_PUBLIC_KEY"));
			aliPayConfig.setAppPrivateKey(propertiesFile.getProperty("ALI_APP_PRIVATE_KEY"));
		}
		//Get access_token of webpage authorization
		AliPayOAuth2Token aliPayOAuth2Token  = AliPayOAuth2Util.getOAuth2AccessToken(aliPayConfig,code);
		//Web Authorization Interface Access Credentials
		String accessToken = aliPayOAuth2Token.getAccessToken();
		//User ID
		aliuserid = aliPayOAuth2Token.getUserid();
		//aliuserid
		redisService.setex(code, 60, aliuserid);
	}
} else {
	aliuserid = redisService.get(code);
}

3. Resolve the expiration of refresh page code

Because auth_code can only be used once when aliuserid is acquired through auth_code, a little trick is used here to resolve the expiration of auth_code when refreshing a web page. When the aliuserid is first acquired, the aliuserid is cached and refreshed to determine that if aliuserid exists, aliuserid is not acquired through codeauth_code. Of course, the other thing worth noting about these two lines of code is that the cached key is the auth_code value.