Currently the spec for DefaultEditorKit.EndOfLineStringProperty says: "When reading a document if a CRLF is encountered a property with this name is added and the value will be "\r\n"." It is not clear.

In fact, the property value stores the line end. It is set when the file is read. When the file is saved, the the value of the 'EndOfLineStringProperty' property is used as the line break written to disk.