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Do a View Source on your page once it gets to the browser and observe what the contents of the do() method have turned into.
P.S. Your subject seems to have nothing to do with your post. Where does the <select> come in? The only reason that this appears to work is that you are calling do() at page load. So it's hard to tell the difference between things that happen on the server and things that happen just before the page is displayed.
If you need to make decisions in the JSP code based upon data and actions that can't be known until after the page is presented to the user (such as selections from a <select> element), your approach completely falls apart.
subject: Good use of JSP for populating textfields