When creating DataContentHandler, defaultCommandMap should be considered.

When creating DataContentHandler, null may be returned from CXF's static CommandMap. DefaultCommandMap from CommandMap.getDefaultCommandMap() could also be used to create DataContentHandler.
Because in RI implementation,xxx.saaj.soap.AttachmentPartImpl,
Some static statement would add specific content handler to default CommandMap.

CommandMap localCommandMap = CommandMap.getDefaultCommandMap();
localMailcapCommandMap.addMailcap("text/xml" + str + "xxx.saaj.soap.XmlDataContentHandler");