Hi Mathew,
The big difference is that servlets are not
thread safe; hence there is no need to pool them. However some containers might maintain a pool of servlet instances in some circumstances. Weblogic for example maintains such a pool for each servlet implementing the
SingleThreadedModel interface. SLSB on the other hand are always pooled because they are designed to be thread safe component and different client threads access a different bean instance.
Regards.