图解servlet
You can see the following illustration to better understand the lifecycle of the Servlet.
When the request of users to Servlet, the servlet will call the method of service() to serve the requirements of users, the service() will call either doGet() or doPost().
The figure below illustrates how WebContainer decided to use Servlet to service request from the client.
https://o7planning.org/en/10169/java-servlet-tutorial
This section explains how to handle the errors notified to Servlet Container.