Re: Class.forName
On Jul 27, 6:03 am, Arne Vajh=F8j <a...@vajhoej.dk> wrote:
Roedy Green wrote:
Is there a way to ask if a class has been loaded without actually
requesting it be loaded? similar to Class.forName
My suggestion would be to use an agent.
import java.lang.instrument.Instrumentation;
public class TraceAgent {
public static void premain(String args, Instrumentation inst) =
{
inst.addTransformer(new TraceTransformer());
}
}
and
import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;
import java.util.HashSet;
import java.util.Set;
public class TraceTransformer implements ClassFileTransformer {
private static Set<String> clz = new HashSet<String>();
public byte[] transform(ClassLoader loader,
String classNa=
me,
Class<?> class=
BeingRedefined,
ProtectionDoma=
in protectionDomain,
byte[] classfi=
leBuffer) throws
IllegalClassFormatException {
clz.add(className.replace("/", "."));
return null;
}
public static boolean isLoaded(String className) {
return clz.contains(className);
}
}
and then check with:
TraceTransformer.isLoaded(clznam)
Arne
Couple of comments on this approach.. the instrumentation subsystem
sometimes passes a null for the classname, so that needs checking to
avoid NPE. Secondly, to avoid totally unnecessary, and increasingly
expensive, rehashing of the Set as it grows, maybe give it an initial
capacity of 10'000 or so. Launching the smallest Java program loads
thousands of classes... Finally, the agent approach requires extra
command line arguments, a JAR etc.. so not really programmer-friendly,
IMO.