异常：
com.github.binarywang.wxpay.exception.WxPayException: 发生异常，解密退款通知加密信息时出错
at com.github.binarywang.wxpay.service.impl.WxPayServiceAbstractImpl.parseRefundNotifyResult(WxPayServiceAbstractImpl.java:135) ~[weixin-java-pay-2.9.0.jar:na]
at com.xhlcgy.weixin.controller.WxPayController.parseRefundNotifyResult(WxPayController.java:290) ~[classes/:na]
at
Caused by: java.security.InvalidKeyException: Invalid AES key length: 31 bytes
at com.sun.crypto.provider.AESCrypt.init(AESCrypt.java:87) ~[sunjce_provider.jar:1.8.0_112]
at com.sun.crypto.provider.ElectronicCodeBook.init(ElectronicCodeBook.java:94) ~[sunjce_provider.jar:1.8.0_112]
at com.sun.crypto.provider.CipherCore.init(CipherCore.java:591) ~[sunjce_provider.jar:1.8.0_112]
at com.sun.crypto.provider.CipherCore.init(CipherCore.java:467) ~[sunjce_provider.jar:1.8.0_112]
at com.sun.crypto.provider.AESCipher.engineInit(AESCipher.java:313) ~[sunjce_provider.jar:1.8.0_112]
at javax.crypto.Cipher.implInit(Cipher.java:802) ~[na:1.8.0_121]
at javax.crypto.Cipher.chooseProvider(Cipher.java:864) ~[na:1.8.0_121]
at javax.crypto.Cipher.init(Cipher.java:1249) ~[na:1.8.0_121]
at javax.crypto.Cipher.init(Cipher.java:1186) ~[na:1.8.0_121]
at com.github.binarywang.wxpay.bean.notify.WxPayRefundNotifyResult.fromXML(WxPayRefundNotifyResult.java:53) ~[weixin-java-pay-2.9.0.jar:na]
... 74 common frames omitted
在退款成功的通知消息的解析中的WxPayRefundNotifyResult.fromXML(xmlData, this.getConfig().getMchKey())方法中一直出现这个异常，最后发现是mchKey，经过加密之后的字符串是0xxxxxx,开头的，在通过
final String keyMd5String = new BigInteger(1, md5.digest()).toString(16).toLowerCase();
上面的bigInteger构造自动将 首位的0省略掉，所以字符串是31位，AES才会报错，所以建议更换其他方式转换成32位字符串
异常：
在退款成功的通知消息的解析中的WxPayRefundNotifyResult.fromXML(xmlData, this.getConfig().getMchKey())方法中一直出现这个异常，最后发现是mchKey，经过加密之后的字符串是0xxxxxx,开头的，在通过
final String keyMd5String = new BigInteger(1, md5.digest()).toString(16).toLowerCase();
上面的bigInteger构造自动将 首位的0省略掉，所以字符串是31位，AES才会报错，所以建议更换其他方式转换成32位字符串