字节跳动大厂面试题详解：聊一下双亲委派机制

import java.io.*;

public class CustomClassLoader extends ClassLoader {
    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        try {
            byte[] data = loadClassData(name);
            return defineClass(name, data, 0, data.length);
        } catch (IOException e) {
            throw new ClassNotFoundException(name);
        }
    }

    private byte[] loadClassData(String className) throws IOException {
        // 从文件中加载类的字节码数据
        InputStream inputStream = getClass().getClassLoader().getResourceAsStream(className.replace(".", "/") + ".class");
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        int bufferSize = 1024;
        byte[] buffer = new byte[bufferSize];
        int bytesNumRead;
        while ((bytesNumRead = inputStream.read(buffer)) != -1) {
            byteArrayOutputStream.write(buffer, 0, bytesNumRead);
        }
        return byteArrayOutputStream.toByteArray();
    }

    public static void main(String[] args) {
        try {
            // 使用自定义类加载器加载类
            Class<?> clazz = new CustomClassLoader().loadClass("com.example.TestClass");
            System.out.println("Class loaded by: " + clazz.getClassLoader());
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

javaCopy code// 自定义类加载器示例
public class CustomClassLoader extends ClassLoader {
    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        // 检查是否允许加载该类
        if (!isClassAllowed(name)) {
            throw new ClassNotFoundException(name + " is not allowed to load.");
        }
        // 加载类的字节码
        byte[] classBytes = loadClassBytes(name);
        // 定义类
        return defineClass(name, classBytes, 0, classBytes.length);
    }

    private boolean isClassAllowed(String className) {
        // 在此处实现类加载的安全策略，例如限制加载某些特定的类
        return !className.startsWith("malicious.");
    }

    private byte[] loadClassBytes(String name) {
        // 从指定位置加载类的字节码，此处省略具体实现
        return null;
    }
}

javaCopy code// 自定义类加载器示例
public class CustomClassLoader extends ClassLoader {
    @Override
    public Class<?> loadClass(String name) throws ClassNotFoundException {
        // 检查是否已加载该类
        Class<?> clazz = findLoadedClass(name);
        if (clazz == null) {
            // 如果没有加载过，则委托给父加载器加载
            clazz = super.loadClass(name);
        }
        return clazz;
    }
}

javaCopy code// 自定义类加载器示例
public class CustomClassLoader extends ClassLoader {
    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        // 从指定位置加载类的字节码
        byte[] classBytes = loadClassBytes(name);
        // 定义类
        return defineClass(name, classBytes, 0, classBytes.length);
    }

    private byte[] loadClassBytes(String name) {
        // 根据不同的版本加载类的字节码，此处省略具体实现
        return null;
    }
}

javaCopy code// 自定义类加载器示例
public class CustomClassLoader extends ClassLoader {
    // 此处省略类加载逻辑
}