下面为你详细介绍使用 Spring Boot 对接支付宝支付，实现支付与退款功能的具体步骤和代码示例。

1. 添加依赖
   在 pom.xml 里添加支付宝 SDK 依赖：

<dependencies><!-- Spring Boot Web --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><!-- 支付宝 SDK --><dependency><groupId>com.alipay.sdk</groupId><artifactId>alipay-sdk-java</artifactId><version>4.10.103.ALL</version></dependency>
</dependencies>

2. 配置支付宝信息
   在 application.yml 中配置支付宝相关信息：

alipay:app-id: your_app_idmerchant-private-key: your_merchant_private_keyalipay-public-key: your_alipay_public_keysign-type: RSA2gateway-url: https://openapi.alipay.com/gateway.donotify-url: your_notify_url

3. 配置支付宝客户端
   创建配置类来初始化支付宝客户端：

import com.alipay.api.AlipayClient;
import com.alipay.api.DefaultAlipayClient;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;@Configuration
public class AlipayConfig {@Value("${alipay.app-id}")private String appId;@Value("${alipay.merchant-private-key}")private String merchantPrivateKey;@Value("${alipay.alipay-public-key}")private String alipayPublicKey;@Value("${alipay.sign-type}")private String signType;@Value("${alipay.gateway-url}")private String gatewayUrl;@Beanpublic AlipayClient alipayClient() {return new DefaultAlipayClient(gatewayUrl, appId, merchantPrivateKey, "json", "UTF-8", alipayPublicKey, signType);}
}

4. 实现支付功能
   创建服务类来处理支付业务逻辑：

import com.alipay.api.AlipayApiException;
import com.alipay.api.AlipayClient;
import com.alipay.api.request.AlipayTradePagePayRequest;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;@Service
public class AlipayService {@Autowiredprivate AlipayClient alipayClient;@Value("${alipay.notify-url}")private String notifyUrl;public String pay(String outTradeNo, String totalAmount, String subject, String body) throws AlipayApiException {AlipayTradePagePayRequest request = new AlipayTradePagePayRequest();request.setReturnUrl(null);request.setNotifyUrl(notifyUrl);request.setBizContent("{\"out_trade_no\":\"" + outTradeNo + "\","+ "\"total_amount\":\"" + totalAmount + "\","+ "\"subject\":\"" + subject + "\","+ "\"body\":\"" + body + "\","+ "\"product_code\":\"FAST_INSTANT_TRADE_PAY\"}");return alipayClient.pageExecute(request).getBody();}
}

5. 实现退款功能
   在服务类中添加退款方法：

import com.alipay.api.AlipayApiException;
import com.alipay.api.AlipayClient;
import com.alipay.api.request.AlipayTradeRefundRequest;
import com.alipay.api.response.AlipayTradeRefundResponse;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;@Service
public class AlipayService {@Autowiredprivate AlipayClient alipayClient;public AlipayTradeRefundResponse refund(String outTradeNo, String refundAmount) throws AlipayApiException {AlipayTradeRefundRequest request = new AlipayTradeRefundRequest();request.setBizContent("{\"out_trade_no\":\"" + outTradeNo + "\","+ "\"refund_amount\":\"" + refundAmount + "\"}");return alipayClient.execute(request);}
}

6. 创建控制器
   创建控制器来处理支付和退款请求：

import com.alipay.api.AlipayApiException;
import com.alipay.api.response.AlipayTradeRefundResponse;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@RestController
@RequestMapping("/alipay")
public class AlipayController {@Autowiredprivate AlipayService alipayService;@GetMapping("/pay")public void pay(@RequestParam String outTradeNo, @RequestParam String totalAmount, @RequestParam String subject, @RequestParam String body, HttpServletResponse response) throws AlipayApiException, IOException {String form = alipayService.pay(outTradeNo, totalAmount, subject, body);response.setContentType("text/html;charset=" + "UTF-8");response.getWriter().write(form);response.getWriter().flush();response.getWriter().close();}@GetMapping("/refund")public AlipayTradeRefundResponse refund(@RequestParam String outTradeNo, @RequestParam String refundAmount) throws AlipayApiException {return alipayService.refund(outTradeNo, refundAmount);}
}

代码解释
依赖添加：引入 Spring Boot Web 和支付宝 SDK 依赖，以支持 Web 开发和支付宝支付功能。
配置信息：在 application.yml 中配置支付宝所需的关键信息，如应用 ID、商户私钥、支付宝公钥等。
支付宝客户端配置：创建 AlipayConfig 类初始化支付宝客户端。
支付服务类：AlipayService 类包含支付和退款的业务逻辑，调用支付宝客户端的方法完成相应操作。
控制器：AlipayController 处理前端的支付和退款请求，调用服务类的方法完成支付和退款操作。
注意事项
要保证私钥和公钥的正确性与安全性。
处理支付和退款回调时，要对签名进行验证，防止数据被篡改。
严格按照支付宝的开发文档进行开发，及时处理可能出现的异常情况。