CGLIB 動態代理實戰：無需接口的高性能代碼生成庫

核心原理

• 基於 ASM 字節碼操作框架，運行時動態生成子類
• 通過繼承目標類、重寫方法實現攔截
• 無需目標類實現接口，補足 JDK 動態代理短板
• 廣泛用於 Spring AOP、Hibernate 等框架

核心 API

基礎示例：自定義攔截器

public class MyMethodInterceptor implements MethodInterceptor {
    public String myFun(String arg) { return "hello, " + arg; }

    @Override
    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) 
            throws Throwable {
        System.out.println("[intercept] before");
        String result = (String) args[0] + "...";
        System.out.println("[intercept] after");
        return result;  // 直接返回，不調用父類方法
    }

    public Object createProxy() {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(MyMethodInterceptor.class);
        enhancer.setCallback(this);
        return enhancer.create();
    }

    public static void main(String[] args) {
        MyMethodInterceptor target = new MyMethodInterceptor();
        MyMethodInterceptor proxy = (MyMethodInterceptor) target.createProxy();
        proxy.myFun("cglib test");  // 觸發攔截
    }
}

通用工具類：Spring 風格封裝

public class MyCGLIBProxy implements MethodInterceptor {
    private Enhancer enhancer = new Enhancer();

    public Object getProxy(Class<?> clazz) {
        enhancer.setSuperclass(clazz);
        enhancer.setCallback(this);
        return enhancer.create();
    }

    @Override
    public Object intercept(Object o, Method method, Object[] args, MethodProxy proxy) 
            throws Throwable {
        System.out.println("cglib before action");
        Object result = proxy.invokeSuper(o, args);  // 調用目標方法
        System.out.println("cglib after action");
        return result;
    }
}

使用方式

MyCGLIBProxy p = new MyCGLIBProxy();
Performer proxy = (Performer) p.getProxy(TargetClass.class);
proxy.perform();  // 自動觸發 before/after

CGLIB vs JDK 動態代理

適用場景

• 第三方庫類無接口、需增強
• Spring AOP 默認策略：有接口用 JDK，無接口用 CGLIB
• 需代理具體類而非接口的場景