说明：  本帖是利用支付宝沙箱测试当面付支付接口，不是官方demo，是我自己写的java简版示例，一个接口一个java 文件，一个main方法，导入环境，修改参数即可运行，demo中会配置个人的沙箱账号信息，方便大家测试。  

测试环境：Eclipse+JDK1.6及以上

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测试流程  

1、创建应用，生成密钥 

2.下载sdk 3.公共参数配置（沙箱环境测试参数）

package com.alipay.config;
  
/**
 * 基本信息配置
 * @author wb-wly251833
 *
 */
public class AlipayConfig {
    //沙箱APPID
    public static final  String app_id = "2016101800718925";
    //沙箱私钥
    public static final  String merchant_private_key = "MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDfDBUJhaw46ck8MHccIBXPt2USOvCRZ0dQNZZwC0EmZvcnL2+NUyoJMbgcV3U5o6wApajkpibf9UkrtYgI3/GZhOgzfzH0IJYAXmYCEniM+Cl5ipIWhY0W/s+uNRGNdXvNlketNNcVqAvkKZdcHz23N60BXsvjdR+BJ/np2CUmr9OCv0aqqwOO190rOuZvVaFCJD5LDmvDFdXPzrJHcOAyYjb2hhJIWt5n4o/b3LMYeuxfwWuQ4VlGx+s0wZJ1udUyAX8X8byqYcnevG8A1sQd/dRVNr8f1BxS8kjDIDljCzKPoYyoaoeJMhJIxrV8gL57oEIX7PbrlvFLplaC7g/XAgMBAAECggEAI4m/SFceC6tkPszSDY8nKoNj/TWa4u/7stH2+D8y0DWTp5CtS202w2RCm3Fr4hUr8KZ0dInso75nPCmeVRupWPaOMLZRdT5D6CciRa4/uuZHZXAouqHoywMqf+1AsLNJWIZbQUOsCW1PB7mAvlLT+H9Md21tOv6MWH3QGewwbytEcri0YkzroQDso3P08xdZDpXtrmg34tLnrNhw+gl8LOtpkbd0SOrGAsoTAE1vTbSLtTR2PAW7RQZkyKW1ansouzwduamFMhTc+DTc40ODJ5b5xlwTDrXn681E7UTX7JytYTPmjrKFHceX9hQ3vxSkm0fEQ7sXoF0pOBL+7AkOIQKBgQD00qCxCSVE8x2Xb/shayGBLCumqIzHtH5Eb42Wz8AOCH2/Ns9HahzXCJfKWhEzWPltYdD34xlu4T+6r7kN9hNNV7PdHRWMMNyFlUrJ8zSzScu13KdQCx9r+JszD8VRRthNHtWDevj83p3qbwr6rNFw6L7nyjxjRE4RaA56gKdQrwKBgQDpOvOz6JaD941qi7jFxnbOZh2OdRrDUHkCG8Cx42eDA83aCCjLJznjJdLXsF2HON2YDcXOn2pHyROks6a+pZZ3nP3VOX5R06QuPrW5cqF3kxO7+v25DVPI4F3VWz+2mbU5uxlqWIRTZikfnvzZeVQcGgFh3ektI6lVDAo6eD/tWQKBgAEy+uiDE/SngDCass8yGCLq1XfmgXIE901cgoQHlng7IGqMWS2PXn7LIvsxv73RpL8daImeSiSZ49cFP1HLL8MEN/RQTSe3oYzh81DT6SErrlzArO0ecNP1jsUMQbopL6wJB6CyPH/4kytvycz6hbgY276E5hDSZ9N7//4nnSovAoGAP9KgCeVl+urtSfC+OXDb5hNPl0I4dqY41vjdPFCsbM/Hrxh4gU9UqfIZxmg+z9gh25A5Rxecr9Q4ieOXh6gsisLtO0ImbSHrVbRXak4SHXSj+9btQ4yAFwI+6zmzL7bUPt4SUGW0oFXefwa0zpZDDAWZxzxAqNePaPSIgAOUCtECgYEA8zySp0UdBQQOEJuTUJlHgf+FK0jUMREVBi9CQgbK8iF/hDmA34B4z0JCkWEsGojiS3S72ZJBXxrZ8RowJGqLuNZHUAD+eEzjoBhZOIfn2R0Bo2UAZAe6pwERzqOEEVLyBExEV3+qkDwIewx4lghFCQpwhO6SNWj4ppSgXh7XAss=";
    //支付宝公钥
    public static final  String alipay_public_key = "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAnVuBUzhfo7kWUN/TS/kHmb4afsAlUVaTR3U5e74V0os1bzlfvh+cpwnwzaEIb36CR1OzeIIzXgARIW/zGAL1/PLG8dFEXQOIGkA0a8YXGVNX9KeWnFCnCQ5gQxrfJ3ryasXzWBxv5bex1VrVsQ2TZ1VdUD+S7dR4SWFHvyck8/xGt3Hz5peUqo/OIlfQpoTBXdqfnJNrTVAMqcQhrIWwgpSVgmUq+UhlZsDaiUvxWWFm9v9nY172jFfzup/DIET//OpIghL6AB2F+ywkCcHdZHiGklnpNoQKQ6XMVKaO/k2nlHU64Y4WGSgJnSG6B798ohZoi3pndrVPAH5+5BKEFQIDAQAB";
    //沙箱网关地址
    public static final  String gatewayUrl = "https://openapi.alipaydev.com/gateway.do";
  
    //正式环境网关地址
//  public static final  String gatewayUrl = "https://openapi.alipay.com/gateway.do";
 
    // 签名方式
    public static String sign_type = "RSA2";
      
    // 字符编码格式
    public static String charset = "utf-8";
  
    public static String format = "json";
  
}

4.执行代码

package com.alipay.demo;
  
import com.alipay.api.AlipayApiException;
import com.alipay.api.AlipayClient;
import com.alipay.api.DefaultAlipayClient;
import com.alipay.api.domain.AlipayTradeRefundModel;
import com.alipay.api.request.AlipayTradeRefundRequest;
import com.alipay.api.response.AlipayTradeRefundResponse;
import com.alipay.config.AlipayConfig;
  
/**
 * 
 * alipay.trade.refund (统一收单交易退款接口)
 * @author wb-wly251833
 *
 */
public class AlipayTradeFefundTest {
    public static void main(String[] args) throws AlipayApiException {
        AlipayClient alipayClient = new DefaultAlipayClient(AlipayConfig.gatewayUrl, AlipayConfig.app_id, AlipayConfig.merchant_private_key, AlipayConfig.format, AlipayConfig.charset, AlipayConfig.alipay_public_key, AlipayConfig.sign_type);
        AlipayTradeRefundRequest request = new AlipayTradeRefundRequest();
        AlipayTradeRefundModel model = new AlipayTradeRefundModel();
        //外部订单号
        model.setOutTradeNo("21070921129550562525");
        //退款金额
        model.setRefundAmount("0.02");
        //标识一次退款请求，同一笔交易多次退款需要保证唯一，如需部分退款，则此参数必传。
        model.setOutRequestNo("HZ01RF2221");
        request.setBizModel(model);
        AlipayTradeRefundResponse response = alipayClient.execute(request);
        if(response.isSuccess()){
            System.out.println("调用成功");
        } else {
            System.out.println("调用失败");
        }
        System.out.println(response.getBody());
    }   
  
      
}

5.demo示例：当面付demo.zip