Then have that as the source of your iframe. Basically the servlet implementation would simply query for the blob then direct the stream from the backend to the servlet output stream. If you search the web for "jsp image blob" or something similar, you should be able to find some sample code. Remember also to consider things like content-type and cache headers.
Alternatively I think there are probably some taglibs to help with this, but personally I prefer option 1.
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