This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
JSP is for outputting HTML or XML. Excel is neither. What you are creating is an HTML table, and then hoping that Excel will be smart enough to automatically import it.
If you want to generate Excel formatted files (like your content type suggests), look at Apache POI. I would also highly recommend implementing it as a Servlet rather than a JSP template, since JSP is not intended or designed for this type of content.
In preparing for battle I have always found that plans are useless, but planning is indispensable. -- Dwight D. Eisenhower