Servlet Sessions: putValue()

[Art Metzer]

A quick question.
Must the object in

public void HttpSession.putValue( String name, Object value )

be a Serializable object? Jason Hunter says in Java Servlet Programming that

You can save any set of arbitrary Java objects in a session object.

If this statement is true, then why doesn't putValue()'s object have to be Serializable?
Thanks,
Art

[maha anna]

Art,
From Servet 2.2 spec

7.7.2 Distributed Environments
Within an application that is marked as distributable, all requests that are part of a session 
can only be handled on a single VM at any one time. In addition all objects placed into instances of the HttpSession class 
using the setAttribute or putValue methods must implement the Serializable interface. The servlet container may throw an 
IllegalArgumentException if a non serializable object is placed into the session.
These restrictions mean that the Developer is ensured that there are no additional concurrency issues beyond those encountered 
in a non-distributed container. In addition, the Container Provider
can ensure scalability by having the ability 
to move a session object, and its contents, from any active node of the distributed system to a different node of the system.

The main reasons for session objects must implement Serializable is, a good servlet container may choose to store the session objects to disk often to reduce the memory usage as well as to reduce the risk of losing the session objects in case of an emergency due to power failure/server failure etc.
regds
maha anna

[This message has been edited by maha anna (edited March 08, 2001).]

[Art Metzer]

Thanks, Maha Anna, that answers it beautifully.
By the way, and since I've got you, I wanted to thank you for your one-stop shopping (can I say that without paying Amazon?) with regards to the Sun Java Certification mock exams! Your efforts were a big help to me.
And thanks again for clarifying putValue().
Art

[maha anna]

Thanks Art! :-) The internet makes it possible. Isn't? One time effort helps many hundreds of people each day.
regds
maha anna