Question

i am working on a GWT web application and i was wondering if there is a way to keep some classes alive on the server.

The point is that i would like to create a static class that will run on the server and manage something for me.. lets say currently logged in users.

public class someclass{

private static someclass instance;
private List<user> users;
private someclass(){
users = new ArrayList<user>();
}
public someclass getInstance()
{
    if (instance == null)
        instance = new someclass(); 
    return instance;
}
public addUser(user u)
{
users.add(user);
}
}

assume that there is no sync needed its not impotent for the question.

lets say first user logs in, and is added to the users list.
when a second user logs in. will the user list be empty? or will it have the old user as well?

Thanks…

Answer 1

There are different ways to do this. However, a very simple way to tackle this scenario would be to use a startup servlet
In web.xml define it as follows.

<servlet>
 <servlet-name>TestServlet</servlet-name>
 <servlet-class>TestServlet</servlet-class>
 <load-on-startup>1</load-on-startup>
</servlet>

Maintain the stat in static fields of that servlet.