Remove or replace xml invalid character reference

I need to remove invalid characters references in xml, that is, if in my xml input has something like



must be removed or replaced. Codes to remove invalid characters in XML does not serve as the input is a stream that has already transformed these characters in numerical references. I know the invalid xml characters are hexadecimal numbers from 20, but I am not knowing how to make the regular expression. I would like to code in Java.