如何在读写过程中在xml文档网中保留doctype信息?

I am reading an xml document, inserting an element and then writing it. In this process, the document loses doctype and dtd info. Through "Transformer" class I can set OutputProperties but my requirement is to insert or update some element and not to play with doctype at all. Could somebody give me a hint?I am reading an xml document, inserting an elem