类加载器上篇：对已有的类进行加密

对一个二进制文件进行加密，令java的类加载器无法识别（不符合类文件结构）

package cn.itcast.cl;

import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;

public class MyClassLoader extends ClassLoader{

    /**把源目录下的二进制文件加密，生成到itcastlib下
     * @param args
     * 源路径G:\Users\king\eclipsespace\classloader\bin\cn\itcast\loadedclass\Attachment.class
     * dest:itcastlib
     */
    public static void main(String[] args) throws Exception {
        // TODO Auto-generated method stub
        String srcPath = args[0];
        String destDir = args[1];
        FileInputStream fis = new FileInputStream(srcPath);
        String destFileName = srcPath.substring(srcPath.lastIndexOf('\\')+1);
        String destPath = destDir + "\\" + destFileName;
        FileOutputStream fos = new FileOutputStream(destPath);
        cypher(fis,fos);
        fis.close();
        fos.close();
    }

    //就异或一下而已，当然可以用更复杂的算法对二进制流进行加密
    private static void cypher(InputStream ips ,OutputStream ops) throws Exception{
        int b = -1;
        while((b=ips.read())!=-1){
            ops.write(b ^ 0xff);
        }
    }

    private String classDir;
    public MyClassLoader(){

    }
    public MyClassLoader(String classDir){
        this.classDir = classDir;
    }
}
//被加载的类

package cn.itcast.loadedclass;
import java.util.Date;

public class Attachment extends Date
{
public String toString(){
return "hello,itcast";
}
}

package cn.itcast.cl;
import cn.itcast.loadedclass.Attachment;
public class CLTest
{
    /**
     * @param args
     */
    public static void main(String[] args)
    {
        System.out.println(CLTest.class.getClassLoader().getClass().getName());
        System.out.println("C++ bootstrap "+System.class.getClassLoader());
        System.out.println("xxx");
        ClassLoader loader = CLTest.class.getClassLoader();
        while(loader != null){
            System.out.println(loader.getClass().getName());
            loader = loader.getParent();
        }
        System.out.println("循环递归向上寻找： "+loader+"\n");
        System.out.println("这是还没把加密类替换原来的类，运行没出错");
        Attachment attachment= new Attachment();
        System.out.println(attachment.toString());
    }

}
sun.misc.Launcher$AppClassLoader
C++ bootstrap null
xxx
sun.misc.Launcher$AppClassLoader
sun.misc.Launcher$ExtClassLoader
循环递归向上寻找： null

这是还没把加密类替换原来的类，运行没出错
hello,itcast

当我把生成的加密类，替换掉以后，一运行马上抛异常，因为加载器无法识别这些乱七八糟的魔数，这样的话就要自己写类加载器来加载了

Exception in thread "main" java.lang.ClassFormatError: Incompatible magic value 889275713 in class file cn/itcast/loadedclass/Attachment

at cn.itcast.cl.CLTest.main(CLTest.java:20)