自定义ClassLoader对Class加密并解密

前言：本博客内容由张孝祥Java高新技术整理而来

class加密部分

项目目录结构

ClassLoaderAttach

package com.dao.chu.myloader;

import java.util.Date;

@SuppressWarnings("serial")
public class ClassLoaderAttach extends Date{

	@Override
	public String toString() {
		return "this is ClassLoaderAttach";
	}
	
}

MyClassLoader

package com.dao.chu.myloader;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class MyClassLoader {
	
	
	public static void main(String[] args) throws IOException {
		
		String srcPath = args[0];
		String destDir = args[1];
		
		String destFileName = srcPath.substring(srcPath.lastIndexOf("\\") + 1);
		String destFilePath = destDir + "\\" + destFileName;
		
		FileInputStream fin = new FileInputStream(srcPath);
		FileOutputStream fout = new FileOutputStream(destFilePath);
		
		cypher(fin,fout);
		
		fin.close();
		fout.close();
	}
	
	/**
	* 
Title: cypher
	* 
Description:加密， 将原来的1改为0,0改为1
	* @param in
	* @param out
	* @throws IOException
	 */
	public static void cypher(InputStream in ,OutputStream out) throws IOException{
		
		int b=0;
		while ((b=in.read())!=-1) {
			out.write(b ^ 0xff);
		}
	}
}

MyClassLoaderTest

package com.dao.chu.myloader;

public class MyClassLoaderTest {

	public static void main(String[] args) {
		
		ClassLoaderAttach classLoaderAttach = new ClassLoaderAttach();
		System.out.println(classLoaderAttach.toString());
	}
}

运行 MyClassLoader，输入ClassLoaderAttach.class的路径和要生成至的路径。

运行成功后可看到有加密后的class文件生成

执行MyClassLoaderTest，可看到正常输出

我们将加密的class文件与原来没加密过的class文件进行替换

再次执行MyClassLoaderTest，可看到报错信息。说明加密成功，用原来的类加载器不能运行，所以我们要用自己的类加载器运行

自定义ClassLoader部分

我们将MyClassLoader修改如下

package com.dao.chu.myloader;

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

public class MyClassLoader extends ClassLoader{
	
	
	public static void main(String[] args) throws IOException {
		
		String srcPath = args[0];
		String destDir = args[1];
		
		String destFileName = srcPath.substring(srcPath.lastIndexOf("\\") + 1);
		String destFilePath = destDir + "\\" + destFileName;
		
		FileInputStream fin = new FileInputStream(srcPath);
		FileOutputStream fout = new FileOutputStream(destFilePath);
		
		cypher(fin,fout);
		
		fin.close();
		fout.close();
	}
	
	/**
	* 
Title: cypher
	* 
Description:加密， 将原来的1改为0,0改为1
	* @param in
	* @param out
	* @throws IOException
	 */
	public static void cypher(InputStream in ,OutputStream out) throws IOException{
		
		int b=0;
		while ((b=in.read())!=-1) {
			out.write(b ^ 0xff);
		}
	}
	
	private String classDir;
	
	public MyClassLoader(){
		
	}
	public MyClassLoader(String classDir){
		this.classDir=classDir;
	}
	
	/**
	 * 覆盖ClassLoader的findClass方法
	 */
	@SuppressWarnings("deprecation")
	@Override
	protected Class findClass(String name)
			throws ClassNotFoundException {
		
		String classFileName = classDir + "\\" + name + ".class";
		try {
			FileInputStream fin = new FileInputStream(classFileName);
			ByteArrayOutputStream baout = new ByteArrayOutputStream();
			//解密
			cypher(fin,baout);
			fin.close();
			//转为字节数组
			byte[] byteArray = baout.toByteArray();
			return defineClass(byteArray, 0, byteArray.length);
			
		} catch (Exception e) {
		}
		
		return null;
	}
	
}

MyClassLoaderTest修改如下

package com.dao.chu.myloader;

import java.util.Date;

public class MyClassLoaderTest {

	@SuppressWarnings("rawtypes")
	public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException {
		
//		ClassLoaderAttach classLoaderAttach = new ClassLoaderAttach();
//		System.out.println(classLoaderAttach.toString());
		
		Class c = new MyClassLoader("myloaderlib").loadClass("ClassLoaderAttach");
		Date d = (Date)c.newInstance();
		System.out.println(d);
		
	}
}

测试前我们需将原来生成的ClassLoaderAttach.class删掉，避免父类加载影响结果

最后执行MyClassLoaderTest

正是我们想要的结果