Constructor of UseBean

Question

Hi Everyone
I am trying to use a parameterized constructor for the Bean which is defined as SESSION scoped. I am wondering whether I've to use jsp:param or jsp:setProperty for passing the values to the constructor. If anybody had done this, kindly guide me.
Thanks in advance.
Raj

Answer 1

Hi Raj,
A few months ago I was wondering the same thing and never got a clear response oddly enough but here's how it is:
The convention for beans is that they do not take parameters in their construction and <jsp:useBean/> makes no provision for that.
I feel your pain. There are some ways around this though.
One is that, if it's a session bean, you can implement HttpSessionBindingListener(HttpSessionBindingEvent e)
which provide notification to your bean when it is placed in a session, i.e. <jsp:useBean ....scope="session"/>, by calling the valueBound() method of the Listener.
You can then use the event's getSession() method to get the session object from which you can obtain Session and ServletContext attributes.
Granted this is not performed on construction but you can fundamentally use this as an init() which will be performed immediatley upon inclusion in the session and so is fairly the same.
There's also the valueUnbound() which is called when the the bean, or whatever class, is about to be released.
Very convenient!
One key point which I've never seen emphasized is that the first call to the <jsp:useBean/> tag will perform the construction and binding...subsequent calls automatically check for prior existence of the bean and so do not call it's constructor or HttpSessionBindingListener.
Another point which I still wonder about is just what is a bean anyway? It is simply a class which abides by a certain convention to permit convenient intuitive (via introspection), parameter passing such as <jsp:...setParameter="*"/>, (maybe not quite right syntax, i forget), whereby all parameters corresponding to the request parameters are set according to the bean's setter methods as named by convention.
I've found that in some cases I'd rather just workup a class which provides the services I require, like a good old fashioned constructor which takes parameters.
If need be I write the code to prevent duplicate construction.
Hey, work's for me. In that case I can use it just like a bean complete with all the getters and setters. If needed just write my own use tags which pass parameters to the constructor.
If anyone wants to blast me for this, have at it...always learning.
Brad