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need clarification about distributed container ??

R K Singh
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Hi there
I have gone through lot of threads in this forum abt this topic by seraching .. But I did not get my answer
AW my question is this.
Q1) What do you mean by container distributed over many VM?
Q2) What is web application? As per definition it is collection of servlet, jSP and other resources.
if I have a directory structure like

which one is my web-app? WebApp01 uses WebApp02.
Q3) If I have a above dir struture, does it means that my container is distributed over VMs as each servlet context will have its own VM.
OR I am worng.. each VM will have its own Context?
Q4)What does Distributed web-app means ?
Is it mean the web app as I have shown above OR web-app which has its servlet over different servers ?
Plz correct me ?
Where are Jason, Satya, ersin, Guy and all ??
[ June 25, 2002: Message edited by: Ravish Kumar ]
R K Singh
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I read this note abt distributed application
Within an application marked as distributable, all requests that are part of a session
must handled by one VM at a time. The container must be able to handle all objects
placed into instances of the HttpSession class using the setAttribute or putValue
methods appropriately. The following restrictions are imposed to meet these conditions:
1. The container must accept objects that implement the Serializable interface
2. The container may choose to support storage of other designated objects in the
HttpSession, such as references to Enterprise JavaBeans and transactions.
3. Migration of sessions will be handled by container-specific facilities.
The servlet container may throw an IllegalArgumentException if an object is
placed into the session that is not Serializable or for which specific support has
not been made available. The IllegalArgumentException must be thrown for
objects where the container cannot support the mechanism necessary for migration
of a session storing them.
These restrictions mean that the Developer is ensured that there are no additional
concurrency issues beyond those encountered in a non-distributed container.
The Container Provider can ensure scalability and quality of service features
like load-balancing and failover 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.
If distributed containers persist or migrate sessions to provide quality of service
features, they are not restricted to using the native JVM Serialization mechanism
for serializing HttpSessions and their attributes. Developers are not
guaranteed that containers will call readObject() and writeObject() methods on
session attributes if they implement them, but are guaranteed that the
Serializable closure of their attributes will be preserved.
Containers must notify any session attributes implementing the
HttpSessionActivationListener during migration of a session. They must notify
listeners of passivation prior to serialization of a session, and of activation after
deserialization of a session.
Developers writing distributed applications should be aware that since the
container may run in more than on Java VM, the developer cannot depend on
static or instance variables for storing application states. They should store such
states using an EJB or a database.
It tells me everything except that WHAT is distributed application ?
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