Servlet and Class instances

Question

Under normal conditions a web-container creates only one instance of servlet.Now the case is I am creating instance of a class in the servlet.So for every request to the servlet does an instance of the class is created?

Answer 1

If you make the instance in a service method (service(), doGet(), doPost() etc...) then yes, each request will create a new instance.
If you create the instance anyplace else, no they will share it.
If you hold the reference to the class in the servlet class level as opposed to storing it in the method which creates and uses it, then you can run into problems as well, since there will be only one reference for all requests.
So generally speaking in Servlets (and in any application you need to worry about thread safety:
This is bad. One object will be used by all requests:
public class BadServlet ... {
    Object myObject = new Object();
    public void doGet(...) ... {
        do something with myObject;
}This is bad. A new instance is made for each request, but only one reference. So one request will end up using another's instance:
public class BadServlet ... {
    Object myObject;
    public void doGet(...)... {
        myObject = new Object();
        do something with myObject;
}This is how you would do it in a thread safe manner:
public class GoodServlet ...{
    public void doGet(...)... {
        Object myObject = new Object();
        //Another method in same class needs a reference?  Pass it as a parameter
        someOtherMethod(myObject);
        //Some other servlet needs access?  Store it in Request scope
        request.setAttribute("myObject", myObject);
        //Some other request needs to access it?  Put it in the session scope
        HttpSession session = request.getSession();
        session.setAttribute("myObject", myObject);
    private void doSomething(Object myObject) ... {
        do something with myObject
}