Originally Posted by a description I found somewhere
The load-on-startup element indicates that a servlet should be loaded on the startup of the web application. This element can take an integer value which indicates the order in which the servlet should be loaded.
If the value is negative, or if this element is not present, the container is at its will as to when it should load the servlet. If the value is a positive integer or 0, the container must load and initialize the servlet when the application is deployed.
Generally the servlets marked with lower integers are loaded before servlets marked with higher integers. The container may choose the order of loading of servlets with the same load-on-start-up value.
