import java.lang.reflect.*;
import java.util.*;
/**
* Demonstration of a ClassLoader
*/
public class ClassLoaderDemo1 extends ClassLoader {
/** The Hashtable to keep track of classes, to avoid re-loading them */
protected Hashtable cache = new Hashtable();
/** data's expected length */
private final int dataLength = 433;
/** data, obtained by dumping a compiled .class file */
private int[] data = {
202, 254, 186, 190, 0, 3, 0, 45, 0, 31,
8, 0, 20, 7, 0, 17, 7, 0, 25, 7,
0, 26, 7, 0, 27, 10, 0, 4, 0, 9,
9, 0, 5, 0, 10, 10, 0, 3, 0, 11,
12, 0, 14, 0, 12, 12, 0, 28, 0, 22,
12, 0, 29, 0, 13, 1, 0, 3, 40, 41,
86, 1, 0, 21, 40, 76, 106, 97, 118, 97,
47, 108, 97, 110, 103, 47, 83, 116, 114, 105,
110, 103, 59, 41, 86, 1, 0, 6, 60, 105,
110, 105, 116, 62, 1, 0, 4, 67, 111, 100,
101, 1, 0, 13, 67, 111, 110, 115, 116, 97,
110, 116, 86, 97, 108, 117, 101, 1, 0, 4,
68, 101, 109, 111, 1, 0, 9, 68, 101, 109,
111, 46, 106, 97, 118, 97, 1, 0, 10, 69,
120, 99, 101, 112, 116, 105, 111, 110, 115, 1,
0, 10, 72, 101, 108, 108, 111, 32, 74, 97,
118, 97, 1, 0, 15, 76, 105, 110, 101, 78,
117, 109, 98, 101, 114, 84, 97, 98, 108, 101,
1, 0, 21, 76, 106, 97, 118, 97, 47, 105,
111, 47, 80, 114, 105, 110, 116, 83, 116, 114,
101, 97, 109, 59, 1, 0, 14, 76, 111, 99,
97, 108, 86, 97, 114, 105, 97, 98, 108, 101,
115, 1, 0, 10, 83, 111, 117, 114, 99, 101,
70, 105, 108, 101, 1, 0, 19, 106, 97, 118,
97, 47, 105, 111, 47, 80, 114, 105, 110, 116,
83, 116, 114, 101, 97, 109, 1, 0, 16, 106,
97, 118, 97, 47, 108, 97, 110, 103, 47, 79,
98, 106, 101, 99, 116, 1, 0, 16, 106, 97,
118, 97, 47, 108, 97, 110, 103, 47, 83, 121,
115, 116, 101, 109, 1, 0, 3, 111, 117, 116,
1, 0, 7, 112, 114, 105, 110, 116, 108, 110,
1, 0, 4, 116, 101, 115, 116, 0, 33, 0,
2, 0, 4, 0, 0, 0, 0, 0, 2, 0,
9, 0, 30, 0, 12, 0, 1, 0, 15, 0,
0, 0, 37, 0, 2, 0, 0, 0, 0, 0,
9, 178, 0, 7, 18, 1, 182, 0, 8, 177,
0, 0, 0, 1, 0, 21, 0, 0, 0, 10,
0, 2, 0, 0, 0, 9, 0, 8, 0, 8,
0, 1, 0, 14, 0, 12, 0, 1, 0, 15,
0, 0, 0, 29, 0, 1, 0, 1, 0, 0,
0, 5, 42, 183, 0, 6, 177, 0, 0, 0,
1, 0, 21, 0, 0, 0, 6, 0, 1, 0,
0, 0, 7, 0, 1, 0, 24, 0, 0, 0,
2, 0, 18
};
/** "load", that is, make up, the data for the class */
private byte[] genClassData(String name) {
if (dataLength != data.length)
throw new IllegalArgumentException("data corrupt");
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 {
/** We can expect to be called to resolve at least demo's
* superclass (java.lang.Object). Fortunatetely, we can just
* use super.findSystemClass() to load such things...
*/
if (name.startsWith("java.")) {
System.out.println("loadClass: SystemLoading " + name);
return findSystemClass(name);
}
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("ClassLoaderDemo1 starting");
ClassLoaderDemo1 loader = new ClassLoaderDemo1();
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");
}
/** Try to load some arbitrary class, to see if our
* ClassLoader gets called.
*/
System.out.println("Trying to load an unrelated class");
java.awt.image.DirectColorModel jnk = new java.awt.image.DirectColorModel(24,8,8,8);
System.out.println("Load an unrelated class - was your ClassLoader called?");
/** Try to instantiate a second ClassLoader */
System.out.println("Trying to install another ClassLoader");
ClassLoaderDemo1 loader2 = new ClassLoaderDemo1();
System.out.println("Instantiated another ClassLoader...");
}
}
|
