Merging template XML with Old Data XMLs

[OlBuck]

I have to a template XML and a old data XML which may not be having the same structure as the template. I need to create a new data XML based on the template XML and populate it with values from the old data XML if they are present. e.g. Template XML - \[code\]<tag1></tag1><tag3></tag3>\[/code\]Old Data XML - \[code\]<tag1>value1</tag1><tag2>value2</tag2>\[/code\]New Data XML - \[code\]<tag1>value1</tag1><tag3></tag3>\[/code\]I need to achieve this using Java. Can this be done using Java XSL Transformers? Or do I need some External APIs?