微信小程序v3统一下单java后台代码

微信小程序v3的统一下单接口需要在Java后台代码中实现，以下是一个简单的示例代码：

import java.util.HashMap;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;
import org.apache.commons.codec.digest.DigestUtils;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;

public class WechatPayUtils {

    private static final String UNIFIED_ORDER_URL = "https://api.mch.weixin.qq.com/v3/pay/transactions/jsapi";
    private static final String MCH_ID = "your_mch_id"; // 商户号
    private static final String MCH_PRIVATE_KEY = "your_mch_private_key"; // 商户私钥
    private static final String SERIAL_NO = "your_serial_no"; // 商户证书序列号
    private static final String API_V3_KEY = "your_api_v3_key"; // APIv3密钥

    /**
     * 发起微信支付下单请求
     * @param openid 用户的openid
     * @param totalFee 订单总金额，单位为分
     * @param outTradeNo 商户订单号
     * @param body 商品描述
     * @param notifyUrl 接收微信支付异步通知回调地址
     * @return JSONObject 包含下单结果的JSON对象
     * @throws Exception
     */
    public static JSONObject makeUnifiedOrder(String openid, int totalFee, String outTradeNo, String body, String notifyUrl) throws Exception {
        SortedMap<String, Object> paramMap = new TreeMap<>();
        paramMap.put("appid", "your_appid"); // 小程序appid
        paramMap.put("mchid", MCH_ID);
        paramMap.put("description", body);
        paramMap.put("out_trade_no", outTradeNo);
        paramMap.put("notify_url", notifyUrl);
        paramMap.put("amount", getAmountMap(totalFee));
        paramMap.put("payer", getPayerMap(openid));
        paramMap.put("sign_type", "RSA");

        // 生成签名
        String sign = generateSignature(JSON.toJSONString(paramMap), MCH_PRIVATE_KEY);

        // 设置请求头
        Map<String, String> headers = new HashMap<>();
        headers.put("Accept", "application/json");
        headers.put("Content-Type", "application/json");
        headers.put("Authorization", getAuthorizationHeader(sign));

        // 发送POST请求
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpPost httpPost = new HttpPost(UNIFIED_ORDER_URL);
        for (Map.Entry<String, String> entry : headers.entrySet()) {
            httpPost.setHeader(entry.getKey(), entry.getValue());
        }
        httpPost.setEntity(new StringEntity(JSON.toJSONString(paramMap)));
        CloseableHttpResponse httpResponse = httpClient.execute(httpPost);

        // 解析响应结果
        JSONObject result = JSON.parseObject(EntityUtils.toString(httpResponse.getEntity()));
        return result;
    }

    /**
     * 获取订单金额信息
     * @param totalFee 订单总金额，单位为分
     * @return 包含订单金额信息的Map对象
     */
    private static Map<String, Object> getAmountMap(int totalFee) {
        Map<String, Object> amountMap = new HashMap<>();
        amountMap.put("total", totalFee);
        amountMap.put("currency", "CNY");
        return amountMap;
    }