在运行时在现有类中生成代码(Java)

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

interface MyInterface {
    void doSomething();
}

class MyInvocationHandler implements InvocationHandler {
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("Before method call");
        // 在这里可以动态生成代码
        System.out.println("After method call");
        return null;
    }
}

public class Main {
    public static void main(String[] args) {
        MyInterface myInterface = (MyInterface) Proxy.newProxyInstance(
                MyInterface.class.getClassLoader(),
                new Class<?>[]{MyInterface.class},
                new MyInvocationHandler()
        );

        myInterface.doSomething();
    }
}

<dependency>
    <groupId>org.javassist</groupId>
    <artifactId>javassist</artifactId>
    <version>3.28.0-GA</version>
</dependency>

import javassist.*;

public class Main {
    public static void main(String[] args) throws Exception {
        ClassPool pool = ClassPool.getDefault();
        CtClass cc = pool.get("com.example.MyClass");

        // 在现有方法前插入新代码
        CtMethod method = cc.getDeclaredMethod("myMethod");
        method.insertBefore("System.out.println(\"Before method call\");");

        // 加载修改后的类
        Class<?> modifiedClass = cc.toClass();

        // 创建修改后的类的实例并调用方法
        Object instance = modifiedClass.newInstance();
        modifiedClass.getMethod("myMethod").invoke(instance);
    }
}