proxy7test

gistfile1.java

import java.time.Duration;
import java.util.Optional;
import java.lang.reflect.*;
 
public class Jre7Test {
	public static interface I7 {
		public void say(String greeting);
	}

	public static interface I8 extends I7 {
		public Optional<Duration> optional(java.time.Duration duration);
		public void say(String greeting);
	}

	public static class MyClass7 implements I7 {
		public void say(String greeting) {
			System.out.println("J7 says: " + greeting);
		}
	}

	public static class MyClass8 extends MyClass7 implements I8 {
		public Optional<Duration> optional(java.time.Duration duration) {
			return Optional.of(duration);
		}
		public void say(String greeting) {
			System.out.println("J8 says: " + greeting);
		}
	}
 
	public static void main(String[] args) {
		InvocationHandler handler = new InvocationHandler() {
			public Object invoke(Object proxy, Method method, Object[] args) {
				try {
					return method.invoke(new MyClass8(), args);
				} catch (Exception e) {
					return new RuntimeException(e);
				}
			}
		};
		I7 proxy = (I7) Proxy.newProxyInstance(Jre7Test.class.getClassLoader(), new Class[] { I7.class } , handler);
		proxy.say("Hello from proxy");
		proxy.getClass().getMethods();
	}
}

gistfile2.txt

"C:\Program Files\Java\jdk1.8.0_45\bin\javac.exe" -source 1.7 -target 1.7 Jre7Test.java
warning: [options] bootstrap class path not set in conjunction with -source 1.7
1 warning

"C:\Program Files\Java\jre7\bin\java.exe" Jre7Test
J7 says: Hello from proxy

I think we can stop the discussion at this point. As long as the use of Reflection API upon JDBC objects is a wanted feature, the idea of sharing one single implementation simply won't work, or it will get too complicated to make it work.

When I started this discussion, I only had the JDBC spec in mind as-is, without any use of Reflection API on the JDBC objects, as neither of our own use cases covers this (we de no use such tools).