自定义类加载器（1）

1.自定义类加载器的作用
其实就是对已经加密的class解密，再加载到虚拟机中

2.生成加密的class文件

被加密的java文件

public interface IUserDao {
    void save();
}
public class UserDao implements IUserDao {
    @Override
    public void save() {
        System.out.print("save method.");
    }
}

加密工具类

public final class DesUtils {
    private static final String DES = "DES";
    private static final String KEY = "4YztMHI7PsT4rLZN";

    private DesUtils() {}

    public static byte[] encode(byte[] bytes) {
        try {
            return encrypt(bytes, KEY.getBytes());
        } catch (Exception e) {
            throw new RuntimeException("encode bytes error.");
        }
    }

    public static byte[] decode(byte[] bytes) {
        try {
            return decrypt(bytes, KEY.getBytes());
        } catch (Exception e) {
            throw new RuntimeException("decode bytes error.");
        }
    }

    private static byte[] encrypt(byte[] src, byte[] key) throws Exception {
        SecureRandom sr = new SecureRandom();
        DESKeySpec dks = new DESKeySpec(key);
        SecretKeyFactory keyFactory = SecretKeyFactory.getInstance(DES);
        SecretKey secretKey = keyFactory.generateSecret(dks);
        Cipher cipher = Cipher.getInstance(DES);
        cipher.init(Cipher.ENCRYPT_MODE, secretKey, sr);
        return cipher.doFinal(src);
    }

    private static byte[] decrypt(byte[] src, byte[] key) throws Exception {
        SecureRandom sr = new SecureRandom();
        DESKeySpec dks = new DESKeySpec(key);
        SecretKeyFactory keyFactory = SecretKeyFactory.getInstance(DES);
        SecretKey secretKey = keyFactory.generateSecret(dks);
        Cipher cipher = Cipher.getInstance(DES);
        cipher.init(Cipher.DECRYPT_MODE, secretKey, sr);
        return cipher.doFinal(src);
    }

    private static String byte2hex(byte[] b) {
        StringBuilder hs = new StringBuilder();
        String temp;
        for (int n = 0; n < b.length; n++) {
            temp = (Integer.toHexString(b[n] & 0XFF));
            if (temp.length() == 1) {
                hs.append("0").append(temp);
            } else {
                hs.append(temp);
            }
        }
        return hs.toString().toUpperCase();

    }

    private static byte[] hex2byte(byte[] b) {
        if ((b.length % 2) != 0) {
            throw new IllegalArgumentException("length not even");
        }
        byte[] b2 = new byte[b.length / 2];
        for (int n = 0; n < b.length; n += 2) {
            String item = new String(b, n, 2);
            b2[n / 2] = (byte) Integer.parseInt(item, 16);
        }
        return b2;
    }
}

生成加密class文件

public static void createEncodeFile() {
    String targetFilePath = "D:\\test\\target\\classes\\test\\UserDao.class";
    String encodedFilePath = "D:\\test\\UserDao.class";
    FileInputStream fis = null;
    FileOutputStream fos = null;
    ByteArrayOutputStream baos = null;
    try {
        fis = new FileInputStream(new File(targetFilePath));
        fos = new FileOutputStream(new File(encodedFilePath));
        baos = new ByteArrayOutputStream();
        byte[] bytes = new byte[1024];
        int len;
        while ((len = fis.read(bytes)) != -1) {
            baos.write(bytes, 0, len);
        }
        byte[] encode = DesUtils.encode(baos.toByteArray());
        fos.write(encode);
        fos.flush();
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        if (Objects.nonNull(fis)) {
            try {
                fis.close();
            } catch (Exception e) {}
        }
        if (Objects.nonNull(fos)) {
            try {
                fos.close();
            } catch (Exception e) {}
        }
        if (Objects.nonNull(baos)) {
            try {
                baos.close();
            } catch (Exception e) {}
        }
    }
}

3.自定义类加载器

public class EncodeClassLoader extends ClassLoader {
    private String filePath = null;

    protected Class<?> findClassByFilePathAndName(String filePath, String name)
            throws ClassNotFoundException {
        if (Objects.isNull(filePath) || Objects.isNull(name)) {
            throw new IllegalArgumentException("参数错误");
        }
        this.filePath = filePath;
        return findClass(name);
    }

    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        StringBuilder stringBuilder = new StringBuilder(filePath)
                .append(name.substring(name.lastIndexOf(".") + 1))
                .append(".class");
        FileInputStream fis = null;
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        try {
            fis = new FileInputStream(new File(stringBuilder.toString()));
            byte[] bytes = new byte[1024];
            int len = -1;
            while ((len = fis.read(bytes)) != -1) {
                baos.write(bytes, 0, len);
            }
            byte[] decodeBytes = DesUtils.decode(baos.toByteArray());
            return this.defineClass(name, decodeBytes, 0, decodeBytes.length);
        } catch (Exception e) {
            throw new ClassNotFoundException();
        } finally {
            closeStream(fis);
            closeStream(baos);
        }
    }

    private void closeStream(OutputStream stream) {
        if (Objects.nonNull(stream)) {
            try {
                stream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    private void closeStream(InputStream stream) {
        if (Objects.nonNull(stream)) {
            try {
                stream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

4.测试

public static void main(String[] args) throws Exception {
    EncodeClassLoader classLoader = new EncodeClassLoader();
    String filePath = "D:\\test\\";
    String name = "test.UserDao";
    try {
        Class<IUserDao> userDaoClass = (Class<IUserDao>) classLoader.findClassByFilePathAndName(filePath, name);
        IUserDao userDao = userDaoClass.newInstance();
        userDao.save();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

自定义类加载器（1）

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