Simple Demonstration of a ClassLoader WILL NOT COMPILE OUT OF THE BOX
/*
* 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");
}
}
}
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