ClassLoaderDemo0.java Source code

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Here is the source code for ClassLoaderDemo0.java

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/*
 * Copyright (c) Ian F. Darwin, http://www.darwinsys.com/, 1996-2002.
 * All rights reserved. Software written by Ian F. Darwin and others.
 * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS''
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * Java, the Duke mascot, and all variants of Sun's Java "steaming coffee
 * cup" logo are trademarks of Sun Microsystems. Sun's, and James Gosling's,
 * pioneering role in inventing and promulgating (and standardizing) the Java 
 * language and environment is gratefully acknowledged.
 * 
 * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for
 * inventing predecessor languages C and C++ is also gratefully acknowledged.
 */

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Hashtable;

/**
 * Simple Demonstration of a ClassLoader WILL NOT COMPILE OUT OF THE BOX -- WILL
 * ONLY WORK AS PART OF THE CLASSLOADER EXERCISE. See ClassLoader1 for a working
 * version.
 */
public class ClassLoaderDemo0 extends ClassLoader {
    /** The Hashtable to keep track of classes, to avoid re-loading them */
    protected Hashtable cache = new Hashtable();

    /** INSERT HERE THE RESULT OF DUMPING DEMO.CLASS */
    byte[] data /* = ... */;

    int dataLength;

    /** END OF INSERTION OF THE RESULT OF DUMPING DEMO.CLASS */

    /** "load", that is, generate, the data for the class */
    private byte[] genClassData(String name) {
        if (dataLength != data.length) // EXPECT COMPILE ERROR in javasrc
            throw new IllegalArgumentException("data corrupt, " + dataLength + "!=" + data.length);
        byte[] bd = new byte[data.length];
        for (int i = 0; i < bd.length; i++)
            bd[i] = (byte) data[i];
        return bd;
    }

    public synchronized Class loadClass(String name, boolean resolve) throws ClassNotFoundException {
        Class c = (Class) cache.get(name);
        if (c == null) {
            // System.out.println("loadClass: About to genClassData " + name);
            byte mydata[] = genClassData(name);
            // System.out.println("loadClass: About to defineClass " + name);
            c = defineClass(name, mydata, 0, mydata.length);
            System.out.println("loadClass: storing " + name + " in cache.");
            cache.put(name, c);
        } else
            System.out.println("loadClass: found " + name + " in cache.");
        if (resolve) {
            System.out.println("loadClass: About to resolveClass " + name);
            resolveClass(c);
        }
        return c;
    }

    public static void main(String[] argv) {
        System.out.println("ClassLoaderDemo starting");
        ClassLoaderDemo0 loader = new ClassLoaderDemo0();
        Class c = null;
        Object demo;
        try {
            /* Load the "Demo" class from memory */

            System.out.println("About to load class  Demo");
            c = loader.loadClass("Demo", true);
            System.out.println("About to instantiate class Demo");
            demo = c.newInstance();
            System.out.println("Got Demo class loaded: " + demo);

            /* Now try to call a method */

            Method mi = c.getMethod("test", null);
            mi.invoke(demo, null);

        } catch (InvocationTargetException e) {
            // The invoked method threw an exception. We get it
            // wrapped up inside another exception, hence the
            // extra call here:
            e.getTargetException().printStackTrace();
            System.out.println("Could not run test method");
        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("Could not run test method");
        }
    }
}