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.
We do not know what exception you faced.
But make sure you are getting "str1" as a request parameter and it is not null.
If you pass any non-numeric value in this request parameter then you will get NumberFormatException too. To avoid this you should validate for the "str1" if its numeric.