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import java.io.File;

import java.io.FileInputStream;

import java.io.IOException;

public class MyClassLoader extends ClassLoader {

    private String classPath;

    // 构造方法，指定加载路径

    public MyClassLoader(String classPath) {

        this.classPath = classPath;

    }

    // 重写 findClass 方法

    @Override

    protected Class<?> findClass(String name) throws ClassNotFoundException {

        byte[] classData = loadClassData(name);

        if (classData == null) {

            throw new ClassNotFoundException();

        }

        return defineClass(name, classData, 0, classData.length);

    }

    // 自定义读取类数据的方法

    private byte[] loadClassData(String className) {

        try {

            // 将包名中的 . 替换为路径分隔符 /

            String fileName = classPath + className.replace('.', '/') + ".class";

            FileInputStream fis = new FileInputStream(new File(fileName));

            byte[] data = new byte[fis.available()];

            fis.read(data);

            fis.close();

            return data;

        } catch (IOException e) {

            e.printStackTrace();

            return null;

        }

    }

}

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public class Main {

    public static void main(String[] args) {

        String classPath = "/my/custom/classes/";

        MyClassLoader myClassLoader = new MyClassLoader(classPath);

        try {

            // 加载 com.example.HelloWorld 类

            Class<?> clazz = myClassLoader.loadClass("com.example.HelloWorld");

            Object instance = clazz.newInstance();

            System.out.println("加载成功！" + instance.getClass().getName());

        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException e) {

            e.printStackTrace();

        }

    }

}