Hi,
Since Java SE 8 introduced default methods in interfaces there was a
question what to do with java.lang.reflect.Proxy API. Nothing was done
to the API at that time, so the default behavior is to proxy default
methods too. InvocationHandler gets invoked for default methods, but it
has not provision to forward such calls to the default implementations
in the interfaces.
I propose a simple API addition that allows calling super default
methods in proxy instances:
http://cr.openjdk.java.net/~plevart/jdk9-dev/Proxy.invokeSuperDefaults/webrev.02/
With this addition one can simply decide in the InvocationHandler what
to do with invocations to default methods and can forward such
invocation to the default implementation:
public class Test {
interface I1 {
default void m() {
System.out.println(" default I1.m() called");
}
}
interface I2 {
default void m() {
System.out.println(" default I2.m() called");
}
}
interface I12 extends I1, I2 {
@Override
void m();
default int sum(int a, int b) {
return a + b;
}
default Object[] concat(Object first, Object... rest) {
Object[] result = new Object[1 + rest.length];
result[0] = first;
System.arraycopy(rest, 0, result, 1, rest.length);
return result;
}
}
public static void main(String[] args) {
InvocationHandler h = (proxy, method, params) -> {
System.out.println("\nInvocationHandler called for: " +
method +
" with parameters: " +
Arrays.toString(params));
if (method.isDefault()) {
try {
return Proxy.invokeSuper(proxy, method, params);
} catch (InvocationTargetException e) {
throw e.getCause();
}
} else {
switch (method.getName()) {
case "m":
System.out.println(" abstract I12.m(): called");
return null;
default:
throw new UnsupportedOperationException(
"Unsupported method: " + method);
}
}
};
I1 i1 = (I1) Proxy.newProxyInstance(
I1.class.getClassLoader(), new Class<?>[]{I1.class}, h);
i1.m();
I2 i2 = (I2) Proxy.newProxyInstance(
I2.class.getClassLoader(), new Class<?>[]{I2.class}, h);
i2.m();
I12 i12 = (I12) Proxy.newProxyInstance(
I12.class.getClassLoader(), new Class<?>[]{I12.class}, h);
i12.m();
System.out.println(" 1 + 2 = " + i12.sum(1, 2));
System.out.println(" [1] concat [2, 3, 4] = " +
Arrays.toString(i12.concat(1, 2, 3, 4)));
}
}
I know FC date is over, but this is really a small change and I have
heard several people that such feature is missing from the Proxy API.
I'm prepared to create jtreg tests covering the specification if this
proposal is accepted.
Regards, Peter
