evaluating sum of limits

evaluating sum of limits

I was given this problem in definite integral and limits chapter $$\lim_{n
\to \infty}\left( \frac{n}{n^2 + 1^2}+ \frac{n}{n^2 + 2^2} + \frac{n}{n^2
+ 3^2 }+........+\frac{n}{n^2 + n^2}\right)$$ which method is used to
evaluate these kind of problems and how do i evaluate this sum of limits ?
I have heard some Riemann's sum is used but i do not know it and how to
solve by that method if you can explain me how its done