Custom class loader encrypts and decrypts classes

If you need to write your own class loader , Just inherit ClassLoader class , rewrite findClass(String className) Method

ClassLoader Superclass loadClass() Method is used to delegate the loading operation of a class to the parent class loader for execution , If the parent class loader cannot load this class , This class loader will be called findClass()
loadClass() This is where the logic of the parental delegation model is implemented , Modifying this method without authorization will cause the model to be destroyed , So in order to ensure that the parental delegation model is not broken , It is recommended not to rewrite loadClass(), But in findClass() Methods that override custom classes in

public class User {
    
    private String name = "Rocky";
    private int age = 18;
    }

Encryption and decryption tool class ：

public class XorEncryptUtil {
    
    private static void xor(InputStream in, OutputStream out) throws IOException {
    
        int ch;
        while ((ch = in.read()) != -1){
    
            ch  = ch^ 0xff;
            out.write(ch);
        }
    }


    public static void encrypt(File src, File des) throws IOException {
    
        FileInputStream in = new FileInputStream(src);
        FileOutputStream out = new FileOutputStream(des);
        xor(in,out);
        in.close();
        out.close();
    }


    public static byte[] decrypt(File src) throws IOException {
    
        FileInputStream in = new FileInputStream(src);
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        xor(in,out);

        byte[] data = out.toByteArray();
        in.close();
        out.close();
        return data;
    }


    public static void main(String[] args) throws IOException {
    
        File src = new File("C:\\Users\\Administrator\\Desktop\\sb\\1.txt");
        File des = new File("C:\\Users\\Administrator\\Desktop\\sb\\2.txt");
        XorEncryptUtil.encrypt(src,des);

        byte[] decrypt = XorEncryptUtil.decrypt(des);
        String s = new String(decrypt);
        System.out.println("s = " + s);


    }
}

classLoader：

public class MyClassLoader extends ClassLoader {
    
    private String basePath;
    private final static  String FILE_EXT = ".class";

    public MyClassLoader(String basePath) {
    
        this.basePath = basePath;
    }

    public MyClassLoader() {
    
    }

    /** *  Decrypt ：  Use your own ClassLoader * @param className * @return */
    private byte[] loadClassData(String className){
    
        try {
    
// String tempName = className.replaceAll("\\.", System.getProperty("file.separator"));
            String tempName = className.replaceAll("\\.", Matcher.quoteReplacement(File.separator));
            File targetFile = new File(basePath + tempName + FILE_EXT);
            return XorEncryptUtil.decrypt(targetFile);
        } catch (IOException e) {
    
            System.out.println("silly b");
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected Class<?> findClass(String className) throws ClassNotFoundException {
    
        byte[] data = this.loadClassData(className);
        return this.defineClass(className, data, 0, data.length);
    }


    public static void main(String[] args) throws IOException, IllegalAccessException, InstantiationException, ClassNotFoundException {
    
        XorEncryptUtil.encrypt(new File("I:\\java\\springsecurity\\springsecuritylearn\\security\\target\\classes\\security\\User.class"),
                new File("C:\\Users\\Administrator\\Desktop\\sb\\User.class"));

        MyClassLoader myClassLoader = new MyClassLoader();
        myClassLoader.basePath = "C:\\Users\\Administrator\\Desktop\\sb\\";
        Class<?> clazz = myClassLoader.findClass("security.User");
        System.out.println(clazz.getClassLoader());
        Object o = clazz.newInstance();
        System.out.println("o = " + o);
    }
}

Problems encountered ：

• NoClassDefFoundError: User (wrong name: security/User)
  Compiled User With package name , The package name is also required for parsing

• java.lang.IllegalArgumentException: character to be escaped is missing

quote ：https://blog.csdn.net/rockvine/article/details/124836389
https://blog.csdn.net/weixin_34321977/article/details/91658732