微信小程序支付ApiV3版本java开发的完整案例

以下是微信小程序支付ApiV3版本java开发的完整案例：

1. 首先，你需要在微信商户平台上创建一个应用并获取到以下信息：

- 商户号（mch_id）
- 商户APIv3密钥（api_key）
- 应用ID（appid）
- 商户证书私钥文件（apiclient_key.pem）
- 商户证书文件（apiclient_cert.pem）
- 微信支付平台证书文件（weixinpay_cert.pem）

2. 接下来，你需要使用Java SDK进行开发，包括以下步骤：

- 导入相关的Java SDK依赖包。
- 构建请求参数，包括HTTP请求头和请求体，其中请求体需要使用商户证书进行签名。
- 发送HTTP请求，并处理响应数据。

以下是一个简单的Java代码片段，演示如何使用Java SDK实现微信小程序支付ApiV3版本：

import com.github.wxpay.sdk.WXPay;
import com.github.wxpay.sdk.WXPayConstants;
import com.github.wxpay.sdk.WXPayUtil;
import org.apache.commons.codec.binary.Base64;
import org.apache.commons.io.FileUtils;
import org.apache.commons.io.IOUtils;
import org.apache.http.HttpEntity;
import org.apache.http.HttpHeaders;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.security.*;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import java.util.HashMap;
import java.util.Map;

public class WxPayApiV3Demo {

    private static final String API_KEY = "商户APIv3密钥";
    private static final String MCH_ID = "商户号";
    private static final String APP_ID = "应用ID";
    private static final String API_BASE_URL = "https://api.mch.weixin.qq.com/";

    private static final String PRIVATE_KEY_FILE = "apiclient_key.pem";
    private static final String CERT_FILE = "apiclient_cert.pem";
    private static final String WEIXINPAY_CERT_FILE = "weixinpay_cert.pem";

    private static final String CHARSET = StandardCharsets.UTF_8.name();

    private static final String API_PAY = "v3/pay/transactions/jsapi";
    private static final String API_CERTIFICATE = "v3/certificates";

    private static PrivateKey privateKey;
    private static X509Certificate certificate;
    private static X509Certificate weixinpayCertificate;

    static {
        try {
            privateKey = loadPrivateKey(new File(PRIVATE_KEY_FILE));
            certificate = loadCertificate(new File(CERT_FILE));
            weixinpayCertificate = loadCertificate(new File(WEIXINPAY_CERT_FILE));
        } catch (Exception e) {
            throw new RuntimeException("Failed to load certificate.", e);
        }
    }

    public static void main(String[] args) throws Exception {
        // 构建请求参数
        Map<String, String> params = new HashMap<>();
        params.put("appid", APP_ID);
        params.put("mchid", MCH_ID);
        params.put("description", "测试商品");
        params.put("out_trade_no", "1234567890");
        params.put("amount", "{\"total\":100,\"currency\":\"CNY\"}");
        params.put("payer", "{\"openid\":\"用户openid\"}");
        params.put("notify_url", "https://example.com/notify");

        // 发送HTTP请求
        String response = doPost(API_PAY, params);
        System.out.println(response);
    }

    private static String doPost(String api, Map<String, String> params) throws Exception {
        String url = API_BASE_URL + api;
        String timestamp = String.valueOf(System.currentTimeMillis() / 1000);

        // 构建请求头
        Map<String, String> headers = new HashMap<>();
        headers.put(HttpHeaders.CONTENT_TYPE, ContentType.APPLICATION_JSON.getMimeType());
        headers.put(HttpHeaders.AUTHORIZATION, buildAuthorizationHeader(api, timestamp, params));

        // 构建请求体
        String requestBody = WXPayUtil.mapToXml(params);
        String signature = sign(requestBody, timestamp);
        String signedRequestBody = buildSignedRequestBody(requestBody, signature);

        // 发送HTTP请求
        HttpPost httpPost = new HttpPost(url);
        headers.forEach(httpPost::addHeader);
        httpPost.setEntity(new StringEntity(signedRequestBody, CHARSET));
        try (CloseableHttpClient httpClient = HttpClients.createDefault();
             CloseableHttpResponse httpResponse = httpClient.execute(httpPost)) {
            HttpEntity entity = httpResponse.getEntity();
            return IOUtils.toString(entity.getContent(), CHARSET);
        }
    }

    private static String buildAuthorizationHeader(String api, String timestamp, Map<String, String> params) throws Exception {
        String nonceStr = WXPayUtil.generateUUID();
        String message = buildMessage(api, timestamp, nonceStr, params);
        String signature = sign(message);

        return String.format("WECHATPAY2-SHA256-RSA2048 mchid=\"%s\",nonce_str=\"%s\",timestamp=\"%s\",serial_no=\"%s\",signature=\"%s\"",
                MCH_ID, nonceStr, timestamp, weixinpayCertificate.getSerialNumber().toString(16), signature);
    }

    private static String buildMessage(String api, String timestamp, String nonceStr, Map<String, String> params) {
        StringBuilder sb = new StringBuilder();
        sb.append("POST\n")
                .append(API_BASE_URL).append(api).append("\n")
                .append(buildQueryString(params)).append("\n")
                .append(HttpHeaders.CONTENT_TYPE).append(":").append(ContentType.APPLICATION_JSON.getMimeType()).append("\n")
                .append(HttpHeaders.ACCEPT).append(":").append(ContentType.APPLICATION_JSON.getMimeType()).append("\n")
                .append(HttpHeaders.AUTHORIZATION).append(":").append(buildAuthorizationHeader(api, timestamp, params)).append("\n")
                .append("Wechatpay-Timestamp:").append(timestamp).append("\n")
                .append("Wechatpay-Nonce:").append(nonceStr).append("\n")
                .append("Wechatpay-Serial:").append(weixinpayCertificate.getSerialNumber().toString(16)).append("\n");

        return sb.toString();
    }

    private static String buildQueryString(Map<String, String> params) {
        StringBuilder sb = new StringBuilder();
        params.entrySet().stream()
                .sorted(Map.Entry.comparingByKey())
                .forEach(entry -> {
                    if (sb.length() > 0) {
                        sb.append("&");
                    }
                    sb.append(entry.getKey()).append("=").append(entry.getValue());
                });
        return sb.toString();
    }

    private static String sign(String message) throws Exception {
        Signature signature = Signature.getInstance("SHA256withRSA");
        signature.initSign(privateKey);
        signature.update(message.getBytes(StandardCharsets.UTF_8));
        return Base64.encodeBase64String(signature.sign());
    }

    private static String sign(String requestBody, String timestamp) throws Exception {
        StringBuilder sb = new StringBuilder();
        sb.append(timestamp).append("\n")
                .append(nonceStr()).append("\n")
                .append(requestBody).append("\n");
        return sign(sb.toString());
    }

    private static String buildSignedRequestBody(String requestBody, String signature) {
        return requestBody.replace("</xml>", String.format("<sign_type><![CDATA[SHA256]]></sign_type><sign><![CDATA[%s]]></sign></xml>", signature));
    }

    private static String nonceStr() {
        return WXPayUtil.generateUUID();
    }

    private static PrivateKey loadPrivateKey(File file) throws IOException, NoSuchAlgorithmException, InvalidKeySpecException {
        byte[] bytes = FileUtils.readFileToByteArray(file);
        PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(bytes);
        KeyFactory factory = KeyFactory.getInstance("RSA");
        return factory.generatePrivate(spec);
    }

    private static X509Certificate loadCertificate(File file) throws IOException, CertificateException {
        byte[] bytes = FileUtils.readFileToByteArray(file);
        return WXPayUtil.loadCertificate(bytes);
    }

}

上述代码中，我们使用了微信提供的Java SDK（https://github.com/wechatpay-apiv3/wechatpay-apache-httpclient），它封装了HTTP请求和签名验证的相关逻辑，并提供了一些实用的工具类。在这个示例中，我们使用了WXPayUtil工具类来进行签名、验签和XML格式的转换。我们还使用了Apache HttpClient来发送HTTP请求。

需要注意的是，该示例中使用的是微信提供的Java SDK中的最新版本，如果你使用的是旧版本，可能会存在一些差异。

此外，该示例中只演示了如何实现支付接口，如果你需要实现其他接口，可以参考微信官方文档（https://wechatpay-api.gitbook.io/wechatpay-api-v3/）。