Be warned, TIFF is not really a format. TIFF stands for Tagged Image File Format. Its really a wrapper for any of a huge number of file formats, each "tagged" to tell the processing code what it really is.
Usually, files you need to process 'in' are in one of the common 'tag' formats, so the usual tools do a great job going to JPEG. Its the output side that requires more careful specification.
In general, I would not try to do this in Java. I'd simply use ImageMagick, a wonderful open source, multi-platform tool that can convert nearly anything to anything.