Concept of Servlets Vs Concept of Struts 2

 
In our previous article we have created a hello world program in struts2, in which I have passed parameter from request and setted in action class via a member variable, which may led you in some confusion, since in case of servlets the member variable in it are shared between all request and only those variable inside doget and dopost methods remains unique. So inorder to know why a member variable in struts 2 remains unique per request, we have look into the conceptual difference between Servlets and Struts 2. This article deals with the same.
 

 
** UPDATE: Struts 2 Complete tutorial now available here.
 
In case of Servlet when we have N number of request then only one object is created out of which N number of Threads are created , in which a request object is created. So the objects inside the thread are safe and not shared with other thread objects.
 
But suppose if the Servlet has Member variable, then those variable are not thread safe, as they are shared between all the threads created for each request.

The above concept is depicted pictographically below.
 

 

Note: Servlet & Struts 1 follows same concept.

In case of struts 2 for N number of request N number of object is created. So in this case, even the member variable for these objects are not shared between objects of other request, that the reason Struts 2 is said to be thread safe.
 

The concept of Struts 2 is depicted pictographically as below.
 

 
In our next article we shall learn about the roles of Action class in struts 2.