Java.lang.String is immutable - it has no setter
method.
Shing.
--- Sri Sankaran <[EMAIL PROTECTED]> wrote:
> I was reading Tapestry In Action and did not
> understand the implication of clustering a mutable
> object. Hope you can explain.
>
> To set the stage, the section states that an app
> server -- such as Web Logic -- broadcasts a change
> to all servers in a cluster in response to an
> invocation of the setAttribute method of an
> HttpSession. The article goes on differentiate
> mutable and immutable objects placed in a session.
> It says that depending on the sequence of the steps,
> the value of a session attribute on server in a
> cluster can be stale. For example:
>
> session.setAttribute("some token", x);
> x.setSomeValue("some value");
>
> In this case, since the object referred to by 'x' is
> being modified *after* a call to setAttribute, it
> may not get propagated to all servers in a cluster.
> The cagey *may not* is because we may get lucky if
> the app server hasn't got around to serializing 'x'
> and broadcasting it, before the application invokes
> the setSomeValue method.
>
> My question is: How is this any different if x were
> an immutable object -- such as a String? Wouldn't
> we have the same problem?
>
> Sri
>
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