Home / FAQ / Core Java Technology / JNI

Davanum Srinivas

import java.io.*;
import java.util.*;

import com.sun.jdi.*;
import com.sun.jdi.connect.*;
import com.sun.jdi.event.*;
import com.sun.jdi.request.*;

public class ShowClassLoaders {
    static final String[] excludes = {
        "java.*",
        "javax.*",
        "sun.*",
        "com.sun.*",
    };

    public static void main(String[] args) {
        try {
            VirtualMachine vm = null;
            LaunchingConnector connector = null;
            for(Iterator i =
            Bootstrap.virtualMachineManager().allConnectors().iterator();
            i.hasNext(); ) {
                Connector c = (Connector)i.next();
                if (c.name().equals("com.sun.jdi.CommandLineLaunch")) {
                    connector = (LaunchingConnector)c;
                }
            }

            Map arguments = connector.defaultArguments();
            Connector.Argument mainArgument =
            (Connector.Argument)arguments.get("main"); StringBuffer
            mainArgs = new StringBuffer(); int i;
            for(i = 0; i < args.length - 1; i++) {
                mainArgs.append(args[i] + " ");
            }   mainArgs.append(args[i]);
            mainArgument.setValue(mainArgs.toString());

            vm = connector.launch(arguments);

            EventRequestManager erm = vm.eventRequestManager();
            ClassPrepareRequest cpr = erm.createClassPrepareRequest();
            for(i = 0; i < excludes.length; i++) {
                cpr.addClassExclusionFilter(excludes[i]);
            }
            cpr.enable();
            Thread eventsListener = new
            DisplayClassLoaders(vm.eventQueue());

            Process p = vm.process();
            new MonitorOutput(p.getErrorStream());
            new MonitorOutput(p.getInputStream());
            
            vm.resume();
            eventsListener.join();
        } catch(Throwable oops) {
            oops.printStackTrace();
        }
    }

    private static class DisplayClassLoaders extends Thread {
        EventQueue eventQueue;

        public DisplayClassLoaders(EventQueue eventQueue) {
            super();
            this.eventQueue = eventQueue;
            start();
        }
        
        public void run() {
            try {
                boolean stop = false;
                do {
                    EventSet eventSet = eventQueue.remove();
                    for(EventIterator i = eventSet.eventIterator();
                    i.hasNext(); ) {
                        Event evt = i.nextEvent();
                        if(evt instanceof ClassPrepareEvent) {
                            ClassPrepareEvent cpe =
                            (ClassPrepareEvent)evt; ReferenceType refType
                            = cpe.referenceType();
                            System.out.println("Loading:" + refType.name()
                            +
                                               ", "       +
                                               refType.classLoader());
                        } else if(evt instanceof VMDisconnectEvent) {
                            stop = true;
                        }
                    }
                    eventSet.resume();
                } while(!stop);
            } catch(Throwable oops) {
                oops.printStackTrace();
            }
        }
    }

    static private class MonitorOutput extends Thread {
        InputStreamReader  in;
        OutputStreamWriter out = new OutputStreamWriter(System.out);

        public void run() {
            try {
                int i;
                char[] buf = new char[256];
                while ((i = in.read(buf, 0, buf.length)) >= 0) {
                    out.write(buf, 0, i);
                }
            } catch(Throwable oops) {
                oops.printStackTrace();
            }
        }

        public MonitorOutput(InputStream in) {
            super();
            this.in = new InputStreamReader(in);
            setDaemon(true);
            start();
        }
    }
}

For example to monitor SwingSet2 demo that ships with JDK, set the CLASSPATH as shown below:

CLASSPATH=C:JDK13lib	ools.jar;C:JDK13demojfcSwingSet2SwingSet2.jar;.;

and then use the following command-line:

java ShowClassLoaders SwingSet2