14. Explain JSP/Servle threading model.

Every Servlet contains a doGet or doPost method.
When we deploy a servlet the init method of the servlet is called. And after it has been deployed on each request of the servlet a separate thread is created to process the doGet/doPost method of the servlet.
So all the instance variables of the servlet are not thread safe.
We can override this behaviour by implementing SingleThreadedModel in the servlet which tells the servlet container to create a new Servlet instance for each client’s request instead of using a single Servlet Instance.
But single threaded model is deprecated now in Servlet 2.4 API. API doc says ” Note that SingleThreadModel does not solve all thread safety issues. For example, session attributes and static variables can still be accessed by multiple requests on multiple threads at the same time, even when SingleThreadModel servlets are used. It is recommended that a developer take other means to resolve those issues instead of implementing this interface, such as avoiding the usage of an instance variable or synchronizing the block of the code accessing those resources. ”

this might be the reason why it has been deprecated.