博主是小菜鳥，這篇文章僅是自己開發的隨筆記錄，不足博友可以指出來，一起進步

1、【微信支付】公眾號支付開發者文檔鏈接地址

https://pay.weixin.qq.com/wiki/doc/api/jsapi.php?chapter=9_4

調用微信退款接口，需要發送特定的xml格式字符串到到微信退款接口；

2、微信申請退款需要雙向證書，

JAVA只需要使用apiclient_cert.p12即可，證書從

https://pay.weixin.qq.com/index.php/core/home/login?return_url=%2F

微信商戶平臺-》賬戶設置-》 API安全 中下載的，下載後解壓到本地一個英文命名的文件夾下；

3、證書解壓之後

如下圖，安裝證書，雙擊apiclient_cert.p12，一直下一步到如下頁面

密碼為商戶號（mch_id），一直下一步，直至提示導入成功，至此證書安裝成功。

4、代碼

　4.1工具類

package com.etom.itoilet.util;

import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.io.StringWriter;
import java.security.MessageDigest;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.UUID;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

import com.etom.itoilet.constants.WXPayConstants;
import com.etom.itoilet.constants.WXPayConstants.SignType;

/**
* 微信支付工具類
*
* @author hongzm
*
* @date 2017年7月17日 上午10:30:00
*/
public class WXPayUtil {
/**
* XML格式字符串轉換為Map
*
* @param strXML XML字符串
* @return XML數據轉換後的Map
* @throws Exception
*/
public static Map<String, String> xmlToMap(String strXML) throws Exception {
try {
Map<String, String> data = new HashMap<String, String>();
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
InputStream stream = new ByteArrayInputStream(strXML.getBytes("UTF-8"));
org.w3c.dom.Document doc = documentBuilder.parse(stream);
doc.getDocumentElement().normalize();
NodeList nodeList = doc.getDocumentElement().getChildNodes();
for (int idx = 0; idx < nodeList.getLength(); ++idx) {
Node node = nodeList.item(idx);
if (node.getNodeType() == Node.ELEMENT_NODE) {
org.w3c.dom.Element element = (org.w3c.dom.Element) node;
data.put(element.getNodeName(), element.getTextContent());
}
}
try {
stream.close();
} catch (Exception ex) {
// do nothing
}
return data;
} catch (Exception ex) {
WXPayUtil.getLogger().warn("Invalid XML, can not convert to map. Error message: {}. XML content: {}", ex.getMessage(), strXML);
throw ex;
}

}

/**
* 將Map轉換為XML格式的字符串
*
* @param data Map類型數據
* @return XML格式的字符串
* @throws Exception
*/
public static String mapToXml(Map<String, String> data) throws Exception {
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder documentBuilder= documentBuilderFactory.newDocumentBuilder();
org.w3c.dom.Document document = documentBuilder.newDocument();
org.w3c.dom.Element root = document.createElement("xml");
document.appendChild(root);
for (String key: data.keySet()) {
String value = data.get(key);
if (value == null) {
value = "";
}
value = value.trim();
org.w3c.dom.Element filed = document.createElement(key);
filed.appendChild(document.createTextNode(value));
root.appendChild(filed);
}
TransformerFactory tf = TransformerFactory.newInstance();
Transformer transformer = tf.newTransformer();
DOMSource source = new DOMSource(document);
transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
transformer.setOutputProperty(OutputKeys.INDENT, "yes");
StringWriter writer = new StringWriter();
StreamResult result = new StreamResult(writer);
transformer.transform(source, result);
String output = writer.getBuffer().toString(); //.replaceAll("\n|\r", "");
try {
writer.close();
}
catch (Exception ex) {
}
return output;
}

/**
* 生成帶有 sign 的 XML 格式字符串
*
* @param data Map類型數據
* @param key API密鑰
* @return 含有sign字段的XML
*/
public static String generateSignedXml(final Map<String, String> data, String key) throws Exception {
return generateSignedXml(data, key, SignType.MD5);
}

/**
* 生成帶有 sign 的 XML 格式字符串
*
* @param data Map類型數據
* @param key API密鑰
* @param signType 簽名類型
* @return 含有sign字段的XML
*/
public static String generateSignedXml(final Map<String, String> data, String key, SignType signType) throws Exception {
String sign = generateSignature(data, key, signType);
data.put(WXPayConstants.FIELD_SIGN, sign);
return mapToXml(data);
}

/**
* 判斷簽名是否正確
*
* @param xmlStr XML格式數據
* @param key API密鑰
* @return 簽名是否正確
* @throws Exception
*/
public static boolean isSignatureValid(String xmlStr, String key) throws Exception {
Map<String, String> data = xmlToMap(xmlStr);
if (!data.containsKey(WXPayConstants.FIELD_SIGN) ) {
return false;
}
String sign = data.get(WXPayConstants.FIELD_SIGN);
return generateSignature(data, key).equals(sign);
}

/**
* 判斷簽名是否正確，必須包含sign字段，否則返回false。使用MD5簽名。
*
* @param data Map類型數據
* @param key API密鑰
* @return 簽名是否正確
* @throws Exception
*/
public static boolean isSignatureValid(Map<String, String> data, String key) throws Exception {
return isSignatureValid(data, key, SignType.MD5);
}

/**
* 判斷簽名是否正確，必須包含sign字段，否則返回false。
*
* @param data Map類型數據
* @param key API密鑰
* @param signType 簽名方式
* @return 簽名是否正確
* @throws Exception
*/
public static boolean isSignatureValid(Map<String, String> data, String key, SignType signType) throws Exception {
if (!data.containsKey(WXPayConstants.FIELD_SIGN) ) {
return false;
}
String sign = data.get(WXPayConstants.FIELD_SIGN);
return generateSignature(data, key, signType).equals(sign);
}

/**
* 生成簽名
*
* @param data 待簽名數據
* @param key API密鑰
* @return 簽名
*/
public static String generateSignature(final Map<String, String> data, String key) throws Exception {
return generateSignature(data, key, SignType.MD5);
}

/**
* 生成簽名. 註意，若含有sign_type字段，必須和signType參數保持一致。
*
* @param data 待簽名數據
* @param key API密鑰
* @param signType 簽名方式
* @return 簽名
*/
public static String generateSignature(final Map<String, String> data, String key, SignType signType) throws Exception {
Set<String> keySet = data.keySet();
String[] keyArray = keySet.toArray(new String[keySet.size()]);
Arrays.sort(keyArray);
StringBuilder sb = new StringBuilder();
for (String k : keyArray) {
if (k.equals(WXPayConstants.FIELD_SIGN)) {
continue;
}
if (data.get(k).trim().length() > 0) // 參數值為空，則不參與簽名
sb.append(k).append("=").append(data.get(k).trim()).append("&");
}
sb.append("key=").append(key);
if (SignType.MD5.equals(signType)) {
return MD5(sb.toString()).toUpperCase();
}
else if (SignType.HMACSHA256.equals(signType)) {
return HMACSHA256(sb.toString(), key);
}
else {
throw new Exception(String.format("Invalid sign_type: %s", signType));
}
}

/**
* 獲取隨機字符串 Nonce Str
*
* @return String 隨機字符串
*/
public static String generateNonceStr() {
return UUID.randomUUID().toString().replaceAll("-", "").substring(0, 32);
}

/**
* 生成 MD5
*
* @param data 待處理數據
* @return MD5結果
*/
public static String MD5(String data) throws Exception {
java.security.MessageDigest md = MessageDigest.getInstance("MD5");
byte[] array = md.digest(data.getBytes("UTF-8"));
StringBuilder sb = new StringBuilder();
for (byte item : array) {
sb.append(Integer.toHexString((item & 0xFF) | 0x100).substring(1, 3));
}
return sb.toString().toUpperCase();
}

/**
* 生成 HMACSHA256
* @param data 待處理數據
* @param key 密鑰
* @return 加密結果
* @throws Exception
*/
public static String HMACSHA256(String data, String key) throws Exception {
Mac sha256_HMAC = Mac.getInstance("HmacSHA256");
SecretKeySpec secret_key = new SecretKeySpec(key.getBytes("UTF-8"), "HmacSHA256");
sha256_HMAC.init(secret_key);
byte[] array = sha256_HMAC.doFinal(data.getBytes("UTF-8"));
StringBuilder sb = new StringBuilder();
for (byte item : array) {
sb.append(Integer.toHexString((item & 0xFF) | 0x100).substring(1, 3));
}
return sb.toString().toUpperCase();
}

/**
* 日誌
* @return
*/
public static Logger getLogger() {
Logger logger = LoggerFactory.getLogger("wxpay java sdk");
return logger;
}

/**
* 獲取當前時間戳，單位秒
* @return
*/
public static long getCurrentTimestamp() {
return System.currentTimeMillis()/1000;
}

/**
* 獲取當前時間戳，單位毫秒
* @return
*/
public static long getCurrentTimestampMs() {
return System.currentTimeMillis();
}

/**
* 生成 uuid， 即用來標識一筆單，也用做 nonce_str
* @return
*/
public static String generateUUID() {
return UUID.randomUUID().toString().replaceAll("-", "").substring(0, 32);
}

}

4.2 微信退款(參數根據開發文檔，代碼裏面並不是全部必需)

/***
* 提交退款處理
*
* @param request
* @param response
* @return
*/
@RequestMapping(value = "/submitrefund.json")
@ResponseBody
public Map<String, Object> applyForRefun(HttpServletRequest request, HttpServletResponse response) {
// 訂單的主鍵
String pk_easyhouse_salelog = request.getParameter(EasyhouseSalelogVO.PK_EASYHOUSE_SALELOG);
// 退款處理原因(不是必須，若傳入，則會在下發給用戶的退款中顯示)
String dispose_reason = request.getParameter(EasyhouseSalelogVO.DISPOSE_REASON);
// 銷售狀態：同意退款：3，拒絕退款：4
Integer sale_type = Integer.valueOf(request.getParameter(EasyhouseSalelogVO.SALE_TYPE));
// 根據pk獲取VO
EasyhouseSalelogVO sale = NWDao.getInstance().queryByPK(EasyhouseSalelogVO.class, pk_easyhouse_salelog);
String xmlStr = "";
String resultXml = "";
Map<String, String> resultMap = new HashMap<String, String>();
// 同意退款
if (sale_type == 3) {
// 公眾賬號ID：登陸微信公眾號後臺-開發-基本配置
String appid = "";
// 微信支付商戶號： mch_id-登陸微信支付後臺，即可看到
String mch_id = "";
// 隨機字符串，長度要求在32位以內,調用工具類中的隨機數生成方法
String nonce_str = WXPayUtil.generateNonceStr();
// 微信訂單號 或者商戶訂單號，二選一，這裏用微信訂單號
String transaction_id = sale.getWx_order_num();
// 商戶退款單號，同一單號多次請求，只退款一次
String out_refund_no = WXPayUtil.generateUUID();
String price = sale.getProduct_saleprice().toString();
Double total_price = Double.valueOf(price);
// 訂單總金額
String total_fee = Integer.toString((int) (total_price * 100));
// 退款總金額
String refund_fee = Integer.toString((int) (total_price * 100));
// 退款原因，會在下發給用戶的退款消息中體現(可不傳入)
String refund_desc = sale.getRefund_reason();
// API密鑰(設置路徑：微信商戶平臺(pay.weixin.qq.com)-->賬戶設置-->API安全-->密鑰設置)
String key = WXPayConstants.KEY;
// 將獲得的信息存入Map集合中
Map<String, String> map = new HashMap<String, String>();
map.put("appid", appid);
map.put("mch_id", mch_id);
map.put("nonce_str", nonce_str);
map.put("transaction_id", transaction_id);
map.put("out_refund_no", out_refund_no);
map.put("total_fee", total_fee);
map.put("refund_fee", refund_fee);
map.put("refund_desc", refund_desc);
try {
// 調用工具類，將Map集合轉化為帶簽名sign的XML格式字符串
xmlStr = WXPayUtil.generateSignedXml(map, key);
// 調用微信退款接口地址
String url = WXPayConstants.DOMAIN_API + WXPayConstants.REFUND_URL_SUFFIX;
// 調用雙向證書，返回xml格式狀態碼
resultXml = ClientCustomSSL.doRefund(url, xmlStr);
// 將返回結果轉換成Map集合
resultMap = WXPayUtil.xmlToMap(resultXml);
} catch (Exception e) {
logger.debug("調用退款接口失敗");
}
// 微信端返回字符串為成功時，退款成功,更新數據
if (resultMap.get("return_code").equals(WXPayConstants.SUCCESS)
&& resultMap.get("result_code").equals(WXPayConstants.SUCCESS)) {
sale.setSale_type(Integer.valueOf(BasicConstants.NUMBER_SALE_TYPE_REFUNDED));
logger.debug("退款成功");
//更新公眾號粉絲表的退款總額、消費總額
FansInfoVO fansInfoVO = userCenterService.getUserInfo(sale.getOpenid());
fansInfoVO.setStatus(VOStatus.UPDATED);
fansInfoVO.setRefund_sum(fansInfoVO.getRefund_sum().add(new UFDouble(refund_fee.toString())));
fansInfoVO.setConsume_sum(fansInfoVO.getConsume_sum().sub(new UFDouble(refund_fee.toString())));
salelogService.saveOrUpdate(fansInfoVO);
} else { // 退款失敗
sale.setSale_type(Integer.valueOf(BasicConstants.NUMBER_SALE_TYPE_REFUNDFAIL));
logger.debug("退款失敗");
// 記錄退款失敗原因
dispose_reason += "," + resultMap.get("err_code_des");
}
} else {
// 退款失敗
sale.setSale_type(Integer.valueOf(BasicConstants.NUMBER_SALE_TYPE_REFUNDFAIL));
logger.debug("拒絕退款，退款失敗");
}
sale.setStatus(VOStatus.UPDATED);
sale.setDispose_reason(dispose_reason);
// 處理人
sale.setPk_user(WebUtilsFactory.getInstance().getLoginInfo().getPk_user());
// 保存退款處理時間
sale.setDispose_time(new UFDateTime(System.currentTimeMillis()));
int resultVO = salelogService.saveOrUpdate(sale);
if (resultVO == 0) {
return this.genAjaxResponse(false, "處理失敗！", null);
}
return this.genAjaxResponse(true, "處理成功！", null);
}

4.3 調用證書類，類裏面需要指向證書安裝的路徑

package com.etom.itoilet.util;

import java.io.File;
import java.io.FileInputStream;
import java.security.KeyStore;
import javax.net.ssl.SSLContext;
import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.conn.ssl.SSLContexts;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
import org.nw.web.utils.WebUtilsFactory;

import com.etom.itoilet.constants.WXGlobal;

/**
* 微信退款
* 創建一個自定義的SSLContext安全連接
*
*/
public class ClientCustomSSL {

public static String doRefund(String url,String data) throws Exception {
//指定讀取證書格式為PKCS12(註意PKCS12證書 是從微信商戶平臺-》賬戶設置-》 API安全 中下載的)
KeyStore keyStore = KeyStore.getInstance("PKCS12");
String fileName = "/cert/apiclient_cert.p12";
// 存放路徑
String path = WebUtilsFactory.getInstance().getClientConfigPath() + fileName;
//讀取本機存放的PKCS12證書文件
FileInputStream instream = new FileInputStream(new File(path));
//FileInputStream instream = new FileInputStream(new File("D:/pkcs12/apiclient_cert.p12"));
try {
//指定PKCS12的密碼(商戶ID)
keyStore.load(instream, WXGlobal.getMch_id().toCharArray());
} finally {
instream.close();
}
SSLContext sslcontext = SSLContexts.custom().loadKeyMaterial(keyStore, WXGlobal.getMch_id().toCharArray()).build();
//指定TLS版本
SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory( sslcontext,new String[] { "TLSv1" },null,SSLConnectionSocketFactory.BROWSER_COMPATIBLE_HOSTNAME_VERIFIER);
//設置httpclient的SSLSocketFactory
CloseableHttpClient httpclient = HttpClients.custom().setSSLSocketFactory(sslsf).build();
try {
HttpPost httpost = new HttpPost(url); // 設置響應頭信息
httpost.addHeader("Connection", "keep-alive");
httpost.addHeader("Accept", "*/*");
httpost.addHeader("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8");
httpost.addHeader("Host", "api.mch.weixin.qq.com");
httpost.addHeader("X-Requested-With", "XMLHttpRequest");
httpost.addHeader("Cache-Control", "max-age=0");
httpost.addHeader("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0) ");
httpost.setEntity(new StringEntity(data, "UTF-8"));
CloseableHttpResponse response = httpclient.execute(httpost);
try {
HttpEntity entity = response.getEntity();
String jsonStr = EntityUtils.toString(response.getEntity(), "UTF-8");
EntityUtils.consume(entity);
return jsonStr;
} finally {
response.close();
}
} finally {
httpclient.close();
}
}

}

微信公眾號退款開發