Graham Lea wrote:
> Trying to get my head around this "distributable" thing....
>
> In the Servlet 2.2 Spec., section 1.6, I read,
>
> "An application marked as distributable must obey a few restrictions so
> that containers that support distributable applications can implement
> features such as clustering and failover."
>
> And in section 9,
>
> "When an application is marked as distributable, the Developer must obey a
> more restrictive set of rules than is expected of a normal web application.
> These specific rules are called out throughout this specification."
>
> However, besides the numerous clarifications for container developers, the
> only restrictions I could see clearly aimed at web application developers
> were in section 4.3.1:
>
> "Context attributes exist locally to the VM in which they were created and
> placed. This prevents the ServletContext from being used as a distributed
> shared memory store."
>
> and section 7.7.2:
>
> "In addition all objects placed into instances of the HttpSession class
> using the setAttribute or putValue methods must implement the Serializable
> interface."
>
> Are these the extent of the restrictions on developers of distributed web
> applications?
> If not, would someone be able to detail the others for me or point me to a
> place where I can find them summarised.
>
These are the restrictions that are documented (although particular containers
might have additional specific restrictions for their own implementations).
The restriction about Serialization of HttpSession attributes means, among
other things, that you will usually not be able to store things like JDBC
connections in a user's session -- such objects often rely on socket
connections to the databasel, which cannot be serialized and transferred to a
different server.
>
> Thanks,
>
> Graham Lea
>
Craig McClanahan
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