Rick, I like your idea, it definitely simplifies things. Since we know
that all classes in the common package are at the same version level, we
can just have a single class (called CommonVersion) that has a single
static method (called something like checkVersion(expectedVersion) to do
what you're describing.
David
Rick Hillegas wrote:
I like the idea of a version number in the interface. We could provide
a utility method so that, at startup, the client and server could
complain if the interface wasn't capable enough. It could work like this:
o The client/server startup code would call this utility method,
passing in the actual and expected version numbers of the interface.
o If the actual version number was less than the expected number, then
the utility could throw an exception.
o The exception would complain that the classpath was mis-wired and
explain how to wire it correctly.
In any event, we should add test cases to our (upcoming) compatibility
test suite.
-Rick
Daniel John Debrunner wrote:
David W. Van Couvering wrote:
Hi, all. Yes, it's your favorite topic. :)
[snipped - good shared code proposal]
The common classes will be placed into both derby.jar and
derbyclient.jar. When you have a classpath with a network client at
one
revision and the embedded driver at another revision, the jar with the
highest revision should always go first,
The issue is how to enforce that. I think it's impossible to enforce
that or guarantee any class path ordering. Remember class path problems
are by far the leading cause of technical support calls related to Java
programs.
What it means is that the interface needs to have a version number that
can be obtained easily, and thus the caller must only use the interface
to the level offered. If a caller was written against version 3, but
only version 2 is available then it can only use version 2
functionality.
Dan.
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