自定义类加载器

public class CryptoClassLoader extends ClassLoader {
	private int key;
	
	public CryptoClassLoader(int k){
		this.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;
		
	}
	
	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();
		}
		
		
	}

}

protected Class findClass(String name)
类加载器应该覆盖该方法,以查找类的字节码,并通过调用defineClass方法将字节码传给虚拟机.

Class defineClass(String name,byte[] data,int offset,int length)

参数   name 类名使用.作为包名分隔符
data 用于存放该类字节码的数组
offset 数组中字节码的起始位置
length 数组中字节码的长度