In which Java class should I wrap my XML file to have the simplest process of saving this XML file to disk

Question

I am creating WSDL file to my web service. I need to choose xmime:expectedContentTypes of my XML attachment. Depending on which xmime:expectedContentTypes I choose my attachment will be converted into corresponding Java class. I.e. if I setapplication/xml as xmime:expectedContentTypes parameter it will map my attachment to javax.xml.transform.Source class.

I need to know which Java class allows the simplest process of saving XML file wrapped in that class object into a disk. Then I can choose corresponding xmime:expectedContentTypes value.