It's not right to mean that Netty is better than tomcat.
The implementation is different. Tomcat uses java NIO to implement servlet 3.1 spec. Meantime, netty uses NIO as well but introduces custom api.
If you want to get insight in how does servlet 3.1 implemeted in Netty, watch this video https://youtu.be/uGXsnB2S_vc
