Access a ViewScoped Managedbean in a Servlet - servlets

Question

do anyone know a way to access a ViewScoped ManagedBean in a Servlet?
I can access a SessionScoped ManagedBean for example that way:
MyBean bean = (MyBean) request.getSession().getAttribute("myBean");
But if I set the scope to ViewScoped it returns null. I know that the reason is that the Servlet try to access the bean to early. But how can I fix this?
The backing bean:
#ManagedBean(name = "statistikHandler")
#SessionScoped //or ViewScoped
public class StatistikHandler {
private Object someAttribute
//Do something nice here
//getter and setter
}
The Servlet:
public class ImageStreamServlet extends HttpServlet {
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
System.out.println("+++++ CALL THE IMAGESERVLET +++++");
//try to "inject" the Bean here
StatistikHandler handler = (StatistikHandler) request.getSession().getAttribute("statistikHandler");
try {
if (handler != null) {
//Do something with the ManagedBean
} else {
System.out.println("HANDLER NOT FOUND");
}
} finally {
}
}
#Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
#Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
}
Thats it. If I set the StatistikHandler to SessionScope it works fine. If I set the Handler to ViewScoped it doesn't work.
first: THX for your awnser.
Arjan Tijms:
The second thing is that the view scope only exists when there's a view being processed. It can't come out of thin air.
That make sense and I know that. I try to explain the flow and hope you will understand me. My english is not the best but I think its enough. So lets try :
I set an request to the view and thus an instance of the view scoped bean. So the view and the bean exist but the servlet isn't required jet.
Now I interact with the view and have to render an other part. Now the servlet is needed for this part and I setup an request to the servlet.
So: View and bean exists as an instance and than ( after an partial reload ) I request the servlet.
Arjan Tijms:
You will have to have some code that stores the reference in request scope, where the Servlet can find it and pick it up.
IMHO thats the important part. As u say i cant pick up a view scoped bean as an session attribute. I thank you very mutsh for this fact because I didn't know that before.
Now I can go on and think about a solution.
Thanks and regards

Answer 1

There are two things to be aware of.
The first is that you can't get an instance of the view scoped bean by asking for a session attribute. Those beans are simply not (directly) stored there.
The second thing is that the view scope only exists when there's a view being processed. It can't come out of thin air.
An example in Java code to illustrate that last statement:
// How to access i here???
while (foo) {
int i = 1;
// ...
}
As i is declared inside the while loop, it doesn't make sense to access it before that loop.
In case of the Servlet, if your Servlet is dispatching within the same request to the Faces Servlet, then you access the view scoped bean afterwards only, and still not directly. You will have to have some code that stores the reference in request scope, where the Servlet can find it and pick it up.
To use the Java analogy again, this would be like:
int bar = 0;
while (foo) {
int i = 1;
// ...
bar = i;
}
// use bar here
If you need the Servlet to set something up that the view scoped bean uses, then store that something in request scope and let the view scoped bean pick it up there. Again the Java analogy of this:
int bar = 23;
while (foo) {
int i = bar;
// ...
}
In other words, use a common "channel" to let those two communicate with each other.