....as if you only want the tiff images to be displayed on to the explorer directly then you can do it by incooperating the tiff plugin into your browser.
That would be a bad solution, as the TIFF plugin is not available for most browsers.
But the original question wasn't about web apps, and there are good reasons why one might want to convert a TIFF to a JPEG. The javax.imageio.ImageIO class makes this quite easy - it can read and write images in various formats. See examples e694 and e695
here for code that does exactly that.
The only complication is that ImageIO doesn't support TIFF out of the box. You need to download TIFF support
from here -version 1.1 is fine- and keep the jar file in your classpath.