Writing EXIF metadata to JPEG in Java

Question

I want to edit GPS tag and save new GPS latitude and longitude to JPEG. Ok I found a Sanselan Java library which lets to do it. There is an example how to write metadata WriteExifMetadataExample end I used changeExifMetadata(File jpegImageFile, File dst) method. It works but this example creates a new photo with new gps latitude/longitude. I would like to set new GPS values on the same photo, how can I do this ?

Generally I want to create application similar to Picasa (photo viewer + google maps) .. and in this case when I drag and drop marker on map I want to save new gps exif metadata to photo.. so according with this example it will be create new photo every time? stupid ...I have a little experience with Java .. any sygestion/example is very usefull for me :)