微信支付开发完之后，客户提出新要求，要求有退款功能，好吧，完整的支付流程也包括退款，干吧。o_o ....
当交易发生之后一段时间内，由于买家或者卖家的原因需要退款时，卖家可以通过退款接口将支付款退还给买家，微信支付将在收到退款请求并且验证成功之后，按照退款规则将支付款按原路退到买家帐号上。微信退款功能对应退款申请接口，关于接口注意事项详见申请退款。
1. 准备步骤
由于我是在服务商模式下开发的，服务商模式下，退款接口需要单独申请权限，详见特约商户退款权限授权及解除操作方法。
退款请求需要双向证书， 详见安全规范。
以上是准备步骤，按照文档一步一步来，应该没问题的。
2. 退款申请
此处直接上代码：
//微信签名需要的参数 Map<String, String> signMap = new HashMap<String, String>(); signMap.put("appid", ""); // 微信分配的公众账号ID signMap.put("mch_id",""); // 微信支付分配的商户号 signMap.put("sub_mch_id",""); // 微信支付分配的子商户号 signMap.put("nonce_str", ""); // 随机数 signMap.put("transaction_id",""); // 微信生成的订单号，在支付通知中有返回 signMap.put("out_trade_no",""); // 商户系统内部订单号，要求32个字符内，只能是数字、大小写字母 signMap.put("out_refund_no",""); // 商户系统内部的退款单号，商户系统内部唯一,同一退款单号多次请求只退一笔 signMap.put("refund_fee","1"); // 退款总金额，单位为分，只能为整数，可部分退款 signMap.put("total_fee","1"); // 订单总金额，单位为分，只能为整数 signMap.put("notify_url",""); // 异步接收微信支付退款结果通知的回调地址，通知URL必须为外网可访问的url，不允许带参数如果参数中传了notify_url，则商户平台上配置的回调地址将不会生效 signMap.put("sign",""); // 签名 String xml = WxPayUtil.getRequestXml(signMap); // 生成xml,微信要求的xml形式 StringBuilder sb2 = new StringBuilder(); /** * JAVA使用证书文件 */ logger.info("加载证书开始=========================================》》》》》"); // 指定读取证书格式为PKCS12 KeyStore keyStore = KeyStore.getInstance("PKCS12"); // 读取本机存放的PKCS12证书文件 FileInputStream instream = new FileInputStream(new File("path")); try { // 指定PKCS12的密码(商户ID) keyStore.load(instream, MCH_ID.toCharArray()); } finally { instream.close(); } //ssl双向验证发送http请求报文 SSLContext sslcontext = null; sslcontext = SSLContexts.custom().loadKeyMaterial(keyStore, MCH_ID.toCharArray()).build(); SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(sslcontext, new String[]{"TLSv1"}, null, SSLConnectionSocketFactory.ALLOW_ALL_HOSTNAME_VERIFIER); CloseableHttpClient httpclient = HttpClients.custom().setSSLSocketFactory(sslsf).build(); HttpPost httppost = new HttpPost("https://api.mch.weixin.qq.com/secapi/pay/refund"); StringEntity se = new StringEntity(xml.toString(), "UTF-8"); httppost.setEntity(se); //定义响应实例对象 CloseableHttpResponse responseEntry = null; String xmlStr2 = null; // 读入响应流中字符串的引用 responseEntry = httpclient.execute(httppost); // 发送请求 HttpEntity entity = responseEntry.getEntity(); // 获得响应实例对象 if (entity != null) { // 读取响应流的内容 BufferedReader bufferedReader = null; bufferedReader = new BufferedReader(new InputStreamReader(entity.getContent(), "UTF-8")); while ((xmlStr2 = bufferedReader.readLine()) != null) { sb2.append(xmlStr2); } } Map<String, String> map = WxPayUtil.doXMLParse(sb2.toString()); logger.info("申请退款接口返回的结果集======>" + map); //return_code为微信返回的状态码，SUCCESS表示申请退款成功，return_msg 如非空，为错误原因 签名失败 参数格式校验错误 if (map.get("return_code").toString().equalsIgnoreCase("SUCCESS") && map.get("result_code").toString().equalsIgnoreCase("SUCCESS")) { logger.info("****************退款申请成功！**********************"); // 修改订单状态为申请退款 // 业务逻辑 } else { logger.info("*****************退款申请失败！*********************"); // 失败处理 }
这里主要是准备微信要求的参数，加载证书，发送退款请求。其中加载证书是加载本地证书，关于获取本地证书二进制流说明一下：
Java中读取本地文件可以通过下面的代码完成，其中path代表文件在当前电脑上的路径。
FileInputStream instream = new FileInputStream(new File("path"));
可以将证书文件置于项目的classpath下，通过获取classpath加上证书文件名(全名，带后缀)来定位证书文件，如何获取classpath，Java工程下主要有以下几种方式：
// 获取classpath的绝对路径 this.getClass().getResource("/").getPath() // 通过线程方式获取classPath的绝对路径 Thread.currentThread().getContextClassLoader().getResource("").getPath() // 通过ClassLoader的静态方法获取classpath的绝对路径 ClassLoader.getSystemResource("").getPath()
通过以上方式获取到的是classpath的绝对路径，这里是动态获取的，好处就是可移植。如果你的证书文件在项目classpath下的子目录中，那就需要使用到路径分隔符，这里最好使用
File.separator，因为在Windows下的路径分隔符和Linux下的路径分隔符是不一样的，如果考虑跨平台，最好是像下面这样写：
File myFile = new File("C:" + File.separator + "tmp" + File.separator, "test.txt");3. 退款结果通知
这一部分是微信主动发起的异步回调通知，回调地址在前面发起退款申请时可以指定，商户端需要提供接口接收微信通知，这里需要注意的是退款结果对重要的数据进行了加密，商户需要用商户秘钥进行解密后才能获得结果通知的内容。
微信官方给出的解密步骤如下：
- 对加密串A做base64解码，得到加密串B
- 对商户key做md5，得到32位小写key* ( key设置路径：微信商户平台(pay.weixin.qq.com)-->账户设置-->API安全-->密钥设置 )
- 用key*对加密串B做AES-256-ECB解密（PKCS7Padding）
主要代码如下，包括两个工具类Base64Util和MD5Util：
public class AESUtil { /** * 密钥算法 */ private static final String ALGORITHM = "AES"; /** * 加解密算法/工作模式/填充方式 */ private static final String ALGORITHM_MODE_PADDING = "AES/ECB/PKCS7Padding"; /** * 生成key */ //微信支付API密钥设置路径：微信商户平台(pay.weixin.qq.com)-->账户设置-->API安全-->密钥设置 private static String paySign = ""; //对商户key做md5，得到32位小写key* private static SecretKeySpec key = new SecretKeySpec(MD5Util.MD5Encode(paySign, "UTF-8").toLowerCase().getBytes(), ALGORITHM); /** * AES加密 * @param data * @return * @throws Exception */ public static String encryptData(String data) throws Exception { Security.addProvider(new BouncyCastleProvider()); // 创建密码器 Cipher cipher = Cipher.getInstance(ALGORITHM_MODE_PADDING, "BC"); // 初始化 cipher.init(Cipher.ENCRYPT_MODE, key); return Base64Util.encode(cipher.doFinal(data.getBytes())); } /** * AES解密 *（1）对加密串A做base64解码，得到加密串B *（2）用key*对加密串B做AES-256-ECB解密（PKCS7Padding） * @param base64Data * @return * @throws Exception */ public static String decryptData(String base64Data) throws Exception { Security.addProvider(new BouncyCastleProvider()); Cipher cipher = Cipher.getInstance(ALGORITHM_MODE_PADDING, "BC"); cipher.init(Cipher.DECRYPT_MODE, key); return new String(cipher.doFinal(Base64Util.decode(base64Data))); } public static void main(String[] args) throws Exception { String A = "微信返回的req_info"; System.out.println(AESUtil.decryptData(A)); } } class MD5Util{ private static String byteArrayToHexString(byte b[]) { StringBuffer resultSb = new StringBuffer(); for (int i = 0; i < b.length; i++) resultSb.append(byteToHexString(b[i])); return resultSb.toString(); } private static String byteToHexString(byte b) { int n = b; if (n < 0) n += 256; int d1 = n / 16; int d2 = n % 16; return hexDigits[d1] + hexDigits[d2]; } public static String MD5Encode(String origin, String charsetname) { String resultString = null; try { resultString = new String(origin); MessageDigest md = MessageDigest.getInstance("MD5"); if (charsetname == null || "".equals(charsetname)) resultString = byteArrayToHexString(md.digest(resultString .getBytes())); else resultString = byteArrayToHexString(md.digest(resultString .getBytes(charsetname))); } catch (Exception exception) { } return resultString; } private static final String hexDigits[] = { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f" }; } class Base64Util{ private static final char S_BASE64CHAR[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'}; private static final byte S_DECODETABLE[]; static { S_DECODETABLE = new byte[128]; for (int i = 0; i < S_DECODETABLE.length; i++) S_DECODETABLE[i] = 127; for (int i = 0; i < S_BASE64CHAR.length; i++) S_DECODETABLE[S_BASE64CHAR[i]] = (byte) i; } private static int decode0(char ibuf[], byte obuf[], int wp) { int outlen = 3; if (ibuf[3] == '=') outlen = 2; if (ibuf[2] == '=') outlen = 1; int b0 = S_DECODETABLE[ibuf[0]]; int b1 = S_DECODETABLE[ibuf[1]]; int b2 = S_DECODETABLE[ibuf[2]]; int b3 = S_DECODETABLE[ibuf[3]]; switch (outlen) { case 1: // '\001' obuf[wp] = (byte) (b0 << 2 & 252 | b1 >> 4 & 3); return 1; case 2: // '\002' obuf[wp++] = (byte) (b0 << 2 & 252 | b1 >> 4 & 3); obuf[wp] = (byte) (b1 << 4 & 240 | b2 >> 2 & 15); return 2; case 3: // '\003' obuf[wp++] = (byte) (b0 << 2 & 252 | b1 >> 4 & 3); obuf[wp++] = (byte) (b1 << 4 & 240 | b2 >> 2 & 15); obuf[wp] = (byte) (b2 << 6 & 192 | b3 & 63); return 3; } throw new RuntimeException("Internal error"); } public static byte[] decode(char data[], int off, int len) { char ibuf[] = new char[4]; int ibufcount = 0; byte obuf[] = new byte[(len / 4) * 3 + 3]; int obufcount = 0; for (int i = off; i < off + len; i++) { char ch = data[i]; if (ch != '=' && (ch >= S_DECODETABLE.length || S_DECODETABLE[ch] == 127)) continue; ibuf[ibufcount++] = ch; if (ibufcount == ibuf.length) { ibufcount = 0; obufcount += decode0(ibuf, obuf, obufcount); } } if (obufcount == obuf.length) { return obuf; } else { byte ret[] = new byte[obufcount]; System.arraycopy(obuf, 0, ret, 0, obufcount); return ret; } } public static byte[] decode(String data) { char ibuf[] = new char[4]; int ibufcount = 0; byte obuf[] = new byte[(data.length() / 4) * 3 + 3]; int obufcount = 0; for (int i = 0; i < data.length(); i++) { char ch = data.charAt(i); if (ch != '=' && (ch >= S_DECODETABLE.length || S_DECODETABLE[ch] == 127)) continue; ibuf[ibufcount++] = ch; if (ibufcount == ibuf.length) { ibufcount = 0; obufcount += decode0(ibuf, obuf, obufcount); } } if (obufcount == obuf.length) { return obuf; } else { byte ret[] = new byte[obufcount]; System.arraycopy(obuf, 0, ret, 0, obufcount); return ret; } } public static void decode(char data[], int off, int len, OutputStream ostream) throws IOException { char ibuf[] = new char[4]; int ibufcount = 0; byte obuf[] = new byte[3]; for (int i = off; i < off + len; i++) { char ch = data[i]; if (ch != '=' && (ch >= S_DECODETABLE.length || S_DECODETABLE[ch] == 127)) continue; ibuf[ibufcount++] = ch; if (ibufcount == ibuf.length) { ibufcount = 0; int obufcount = decode0(ibuf, obuf, 0); ostream.write(obuf, 0, obufcount); } } } public static void decode(String data, OutputStream ostream) throws IOException { char ibuf[] = new char[4]; int ibufcount = 0; byte obuf[] = new byte[3]; for (int i = 0; i < data.length(); i++) { char ch = data.charAt(i); if (ch != '=' && (ch >= S_DECODETABLE.length || S_DECODETABLE[ch] == 127)) continue; ibuf[ibufcount++] = ch; if (ibufcount == ibuf.length) { ibufcount = 0; int obufcount = decode0(ibuf, obuf, 0); ostream.write(obuf, 0, obufcount); } } } public static String encode(byte data[]) { return encode(data, 0, data.length); } public static String encode(byte data[], int off, int len) { if (len <= 0) return ""; char out[] = new char[(len / 3) * 4 + 4]; int rindex = off; int windex = 0; int rest; for (rest = len - off; rest >= 3; rest -= 3) { int i = ((data[rindex] & 255) << 16) + ((data[rindex + 1] & 255) << 8) + (data[rindex + 2] & 255); out[windex++] = S_BASE64CHAR[i >> 18]; out[windex++] = S_BASE64CHAR[i >> 12 & 63]; out[windex++] = S_BASE64CHAR[i >> 6 & 63]; out[windex++] = S_BASE64CHAR[i & 63]; rindex += 3; } if (rest == 1) { int i = data[rindex] & 255; out[windex++] = S_BASE64CHAR[i >> 2]; out[windex++] = S_BASE64CHAR[i << 4 & 63]; out[windex++] = '='; out[windex++] = '='; } else if (rest == 2) { int i = ((data[rindex] & 255) << 8) + (data[rindex + 1] & 255); out[windex++] = S_BASE64CHAR[i >> 10]; out[windex++] = S_BASE64CHAR[i >> 4 & 63]; out[windex++] = S_BASE64CHAR[i << 2 & 63]; out[windex++] = '='; } return new String(out, 0, windex); } public static void encode(byte data[], int off, int len, OutputStream ostream) throws IOException { if (len <= 0) return; byte out[] = new byte[4]; int rindex = off; int rest; for (rest = len - off; rest >= 3; rest -= 3) { int i = ((data[rindex] & 255) << 16) + ((data[rindex + 1] & 255) << 8) + (data[rindex + 2] & 255); out[0] = (byte) S_BASE64CHAR[i >> 18]; out[1] = (byte) S_BASE64CHAR[i >> 12 & 63]; out[2] = (byte) S_BASE64CHAR[i >> 6 & 63]; out[3] = (byte) S_BASE64CHAR[i & 63]; ostream.write(out, 0, 4); rindex += 3; } if (rest == 1) { int i = data[rindex] & 255; out[0] = (byte) S_BASE64CHAR[i >> 2]; out[1] = (byte) S_BASE64CHAR[i << 4 & 63]; out[2] = 61; out[3] = 61; ostream.write(out, 0, 4); } else if (rest == 2) { int i = ((data[rindex] & 255) << 8) + (data[rindex + 1] & 255); out[0] = (byte) S_BASE64CHAR[i >> 10]; out[1] = (byte) S_BASE64CHAR[i >> 4 & 63]; out[2] = (byte) S_BASE64CHAR[i << 2 & 63]; out[3] = 61; ostream.write(out, 0, 4); } } public static void encode(byte data[], int off, int len, Writer writer) throws IOException { if (len <= 0) return; char out[] = new char[4]; int rindex = off; int rest = len - off; int output = 0; do { if (rest < 3) break; int i = ((data[rindex] & 255) << 16) + ((data[rindex + 1] & 255) << 8) + (data[rindex + 2] & 255); out[0] = S_BASE64CHAR[i >> 18]; out[1] = S_BASE64CHAR[i >> 12 & 63]; out[2] = S_BASE64CHAR[i >> 6 & 63]; out[3] = S_BASE64CHAR[i & 63]; writer.write(out, 0, 4); rindex += 3; rest -= 3; if ((output += 4) % 76 == 0) writer.write("\n"); } while (true); if (rest == 1) { int i = data[rindex] & 255; out[0] = S_BASE64CHAR[i >> 2]; out[1] = S_BASE64CHAR[i << 4 & 63]; out[2] = '='; out[3] = '='; writer.write(out, 0, 4); } else if (rest == 2) { int i = ((data[rindex] & 255) << 8) + (data[rindex + 1] & 255); out[0] = S_BASE64CHAR[i >> 10]; out[1] = S_BASE64CHAR[i >> 4 & 63]; out[2] = S_BASE64CHAR[i << 2 & 63]; out[3] = '='; writer.write(out, 0, 4); } } }
需要添加的依赖：
<dependency>
<groupId>org.bouncycastle</groupId>
<artifactId>bcprov-jdk15on</artifactId>
<version>1.47</version>
</dependency>4. 遇到的问题
解密时报java.security.InvalidKeyException: Illegal key size
原因：Illegal key size or default parameters 是指密钥长度受限制，java运行时环境读到的是受限的policy文件，policy文件位于${java_home}/jre/lib/security 目录下，这种限制是因为美国对软件出口的控制。
解决：
- 在官方网站下载JCE无限制权限策略文件，下载地址：JDK6、JDK7、JDK8；
- 下载后解压，可以看到local_policy.jar和US_export_policy.jar以及readme.txt；
- 如果安装了JDK，将两个jar文件放到%JDK_HOME%\jre\lib\security目录下覆盖原来文件；
- 如果安装了JRE，将两个jar文件放到%JRE_HOME%\lib\security目录下覆盖原来的文件；
5. 总结
总的来说微信支付退款申请接口比较简单，参考了一些博客之后，顺利的测通了，效果如下：
6. 参考文献
2018.05.24 解密微信退款结果通知中的加密信息req_info
Java实现AES加密,异常java.security.InvalidKeyException: Illegal key size 的解决