To generate xml with jaxb on the fly

I want to create an xml dynamically where the xsd will be provided. Here In the program itself I am able to generate the jaxb object with the name of the xsd that I have given. I want to compile this class on the fly and have to unmarshall the xml (Here the jaxb object is unknown). Can anybody help me in doing this? Is there any better option to do this. Here the xml generated should have some variables statically filled while some should be dynamically filled.