In the process of xml development, call the other party's webservice, the interface is the parameter to receive the xml string, the error is as follows
java.lang.Exception: Malformed XML document: content not allowed in prolog
It was found that it was the required xml format string, but it was caused by a non-xml content.
Error means something that should not appear in the forward declaration of xml. In fact, in my scenario, there is no xml prepended header information at all.