Re: Class.forName

From:
=?ISO-8859-1?Q?Arne_Vajh=F8j?= <arne@vajhoej.dk>
Newsgroups:
comp.lang.java.programmer
Date:
Sun, 27 Jul 2008 00:03:32 -0400
Message-ID:
<488bf392$0$90276$14726298@news.sunsite.dk>
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 className,
                             Class<?> classBeingRedefined,
                             ProtectionDomain protectionDomain,
                             byte[] classfileBuffer) 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

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