Servlet：Singleton，Singlethread或Multi Instance Multithread

Question

This question has been asked previously and discussed before but i want to ask it further.

1. Are Servlets Singleton or not ? According to me they are initialized only by the container but they are still not singleton ?? why ??

2. Are Servlets Single Thread or multi Threaded (Forget about javax.servlet.SingleThreadModel class) ie What happens when there are multiple requests for a single servlet ?? If they are executed conncurrently, that means it is multi threaded ?? and if its multi threaded then each thread will have an instance of the servlet, which contradicts with the 1st point !!

What i think is, Whenever theres a new request, The container creates a new Thread for the incoming Request say Req1, in that it calls or dispatches the control to the service method of servlet. Now this execution happens concurrenlty.. i guess so...

Does my working stands the same in a MVC envirionment ?? (say Struts 1/2, Springs)

Answer 1

The fact that exists just one instance doesn't means it isn't multithread. More thread can concurrently call tha same method of the same instance. Servlets are absolutly multithread.

Answer 2

Servlets are multithreaded - this is the base for their efficiency. One can use "implements SingleThreadModel" to make a servlet single-threaded, so for every request a new object will be created.

Recently this interface SingleThreadModel was deprecated

Answer 3

It depends on the implementation. The servlet interface doesn't specify. http://docs.oracle.com/javaee/5/api/javax/servlet/Servlet.html

However, if you see the HttpServlet then you can see it specifies that it should be synchronized. http://docs.oracle.com/javaee/5/api/javax/servlet/http/HttpServlet.html

Answer 4

也许，下面链接中给出的图表说明了一切...... http://www.tutorialspoint.com/servlets/servlets-life-cycle.htm