Re: Pre-processing during build

On Tue, 16 Jun 2015 21:18:17 +0200, "Markus KARG" <markus@headcrashing.eu>
wrote:
> To make things a bit more clear: It is NOT about whether or not an
> interface method has a parameter of an unknown type. It is solely about
> whether that method is actually INVOKED at runtime. As a JDBC42 is
unknown
> to a JDBC3 client, that client CANNOT invoke that method, hence NEVER a
> ClassNotFoundException can ever happen. Actually the cause of the
exception
> is not even the method invocation but it is solely the instantiation of
the
> parameter value which happens IN THE CALLER. We're pretty safe I think.
So
> still I do not see any need for separate JARs for the purpose of serving
> multiple JDBC levels, as long as the byte code is Java 6 level.

When I tried it in the past (for Jaybird) I ran into problems, it might
have been an IncompatibleClassChangeError (or subclass) on classloading
time, but I can't remember the exact details. I tried reading the JLS and
JVM spec on this point, but I find it hard to come to a conclusion, so I
will try a small experiment this weekend.

However that is half of your problem. The other half is that you risk
using classes, methods or maybe even features that are not available in a
lower Java version and that will not be detected compile time, but only at
runtime (and not just in newly added JDBC 4.2 methods).

On top of that, for a compliant JDBC 4.2 implementation, you must support
java.time objects in setObject, getObject, updateObject, etc. If you want
to do this in a unified source, you will need to load a delegated
implementation that is appropriate for the Java version, otherwise you will
get ClassNotFoundException.

For example in Jaybird we did this:
https://github.com/FirebirdSQL/jaybird/blob/master/src/main/org/firebirdsql/jdbc/field/FBField.java#L739

Which uses (for JDBC 4.2):
https://github.com/FirebirdSQL/jaybird/blob/master/src/jdbc_42/org/firebirdsql/jdbc/field/JDBC42ObjectConverter.java

And for JDBC 4.1 (and 4.0 in Jaybird 2.2):
https://github.com/FirebirdSQL/jaybird/blob/master/src/main/org/firebirdsql/jdbc/field/DefaultObjectConverter.java

Mark