用HttpClientUtil.doPostXml(unifiedorder_url, xml)，签名错误，签名校验正确， 统一下单接口unifiedorder_url:https://api.mch.weixin.qq.com/pay/unifiedorder xmlStr:<xml><return_code><![CDATA[FAIL]]></return_code> <return_msg><![CDATA[签名错误，请检查后再试]]></return_msg> </xml>

{return_msg=不识别的参数appId, return_code=FAIL}