| 发表于：2007-02-26 13:38:065楼 得分:20 |
重写classloader的部分方法，对加载进来的.class进行字节加减来实现基本的加密和解秘
import java.util.*;
import java.io.*;
import java.lang.reflect.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
/**
this program demonstrates a custom class loader that decrypts
class files.
*/
public class classloadertest
{
public static void main（string[] args)
{
jframe frame = new classloaderframe（);
frame.setdefaultcloseoperation（jframe.exit_on_close);
frame.setvisible（true);
}
}
/**
this frame contains two text fields for the name of the class
to load and the decryption key.
*/
class classloaderframe extends jframe
{
public classloaderframe（)
{
settitle（ "classloadertest ");
setsize（default_width, default_height);
setlayout（new gridbaglayout（));
add（new jlabel（ "class "), new gbc（0, 0).setanchor（gbc.east));
add（namefield, new gbc（1, 0).setweight（100, 0).setanchor（gbc.west));
add（new jlabel（ "key "), new gbc（0, 1).setanchor（gbc.east));
add（keyfield, new gbc（1, 1).setweight（100, 0).setanchor（gbc.west));
jbutton loadbutton = new jbutton（ "load ");
add（loadbutton, new gbc（0, 2, 2, 1));
loadbutton.addactionlistener（new
actionlistener（)
{
public void actionperformed（actionevent event)
{
runclass（namefield.gettext（), keyfield.gettext（));
}
});
pack（);
}
/**
runs the main method of a given class.
@param name the class name
@param key the decryption key for the class files
*/
public void runclass（string name, string key)
{
try
{
classloader loader = new cryptoclassloader（integer.parseint（key));
class c = loader.loadclass（name);
string[] args = new string[] {};
method m = c.getmethod（ "main ", args.getclass（));
m.invoke（null, （object) args);
}
catch （throwable e)
{
joptionpane.showmessagedialog（this, e);
}
}
private jtextfield keyfield = new jtextfield（ "3 ", 4);
private jtextfield namefield = new jtextfield（30);
private static final int default_width = 300;
private static final int default_height = 200;
}
/**
this class loader loads encrypted class files.
*/
class cryptoclassloader extends classloader
{
/**
constructs a crypto class loader.
@param k the decryption key
*/
public cryptoclassloader（int k)
{
key = k;
}
protected class findclass（string name)
throws classnotfoundexception
{
byte[] classbytes = null;
try
{
classbytes = loadclassbytes（name);
}
catch （ioexception e)
{
throw new classnotfoundexception（name);
}
class cl = defineclass（name, classbytes, 0, classbytes.length);
if （cl == null)
throw new classnotfoundexception（name);
return cl;
}
/**
loads and decrypt the class file bytes.
@param name the class name
@return an array with the class file bytes
*/
private byte[] loadclassbytes（string name)
throws ioexception
{
string cname = name.replace（ '. ', '/ ') + ".caesar ";
fileinputstream in = null;
in = new fileinputstream（cname);
try
{
bytearrayoutputstream buffer = new bytearrayoutputstream（);
int ch;
while （（ch = in.read（)) != -1)
{
byte b = （byte) （ch - key);
buffer.write（b);
}
in.close（);
return buffer.tobytearray（);
}
finally
{
in.close（);
}
}
private int key;
}
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