java動(dòng)態(tài)代理怎么實(shí)現(xiàn)

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Java 動(dòng)態(tài)代理可以通過以下幾種方式實(shí)現(xiàn)：

使用 java.lang.reflect.Proxy 類：Proxy類提供了一個(gè)靜態(tài)方法 newProxyInstance()，可以通過傳入目標(biāo)對(duì)象的類加載器、目標(biāo)對(duì)象實(shí)現(xiàn)的接口和InvocationHandler 接口的實(shí)現(xiàn)類來創(chuàng)建代理對(duì)象。InvocationHandler接口的實(shí)現(xiàn)類負(fù)責(zé)處理代理對(duì)象的方法調(diào)用。代理對(duì)象在調(diào)用方法時(shí)，會(huì)把方法調(diào)用轉(zhuǎn)發(fā)給 InvocationHandler 的invoke()方法，從而實(shí)現(xiàn)代理功能。

public interface Subject {void doSomething();
}

public class RealSubject implements Subject {public void doSomething() {System.out.println("RealSubject doSomething");
    }
}

public class MyInvocationHandler implements InvocationHandler {private Subject target;

    public MyInvocationHandler(Subject target) {this.target = target;
    }

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {System.out.println("Before method invoke");
        Object result = method.invoke(target, args);
        System.out.println("After method invoke");
        return result;
    }
}

public class Main {public static void main(String[] args) {Subject realSubject = new RealSubject();
        Subject proxySubject = (Subject) Proxy.newProxyInstance(realSubject.getClass().getClassLoader(),
                realSubject.getClass().getInterfaces(),
                new MyInvocationHandler(realSubject));
        proxySubject.doSomething();}
}

使用 CGLib 庫(kù)：CGLib是一個(gè)基于 ASM 框架的字節(jié)碼生成庫(kù)，它可以在運(yùn)行時(shí)動(dòng)態(tài)生成目標(biāo)對(duì)象的子類，并覆蓋其中的方法以實(shí)現(xiàn)代理功能。

public interface Subject {void doSomething();
}

public class RealSubject implements Subject {public void doSomething() {System.out.println("RealSubject doSomething");
    }
}

public class MyMethodInterceptor implements MethodInterceptor {public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {System.out.println("Before method invoke");
        Object result = proxy.invokeSuper(obj, args);
        System.out.println("After method invoke");
        return result;
    }
}

public class Main {public static void main(String[] args) {Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(RealSubject.class);
        enhancer.setCallback(new MyMethodInterceptor());
        Subject proxySubject = (Subject) enhancer.create();
        proxySubject.doSomething();}
}

需要注意的是，使用 CGLib 實(shí)現(xiàn)動(dòng)態(tài)代理時(shí)，目標(biāo)對(duì)象不能是 final 類或者包含 final 方法，因?yàn)?CGLib 是通過生成目標(biāo)對(duì)象的子類來實(shí)現(xiàn)代理的。

使用 ByteBuddy 庫(kù)：ByteBuddy是一個(gè)輕量級(jí)的字節(jié)碼操作庫(kù)，它可以在運(yùn)行時(shí)動(dòng)態(tài)生成目標(biāo)對(duì)象的子類，并覆蓋其中的方法以實(shí)現(xiàn)代理功能。

public interface Subject {void doSomething();
}

public class RealSubject implements Subject {public void doSomething() {System.out.println("RealSubject doSomething");
    }
}

public class MyInterceptor implements MethodInterceptor {public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {System.out.println("Before method invoke");
        Object result = proxy.invokeSuper(obj, args);
        System.out.println("After method invoke");
        return result;
    }
}

public class Main {public static void main(String[] args) throws Exception {Class<? extends Subject> proxyClass = new ByteBuddy()
                .subclass(Subject.class)
                .method(any()).intercept(MethodDelegation.to(MyInterceptor.class))
                .make()
                .load(RealSubject.class.getClassLoader())
                .getLoaded();
        Subject proxySubject = proxyClass.getDeclaredConstructor().newInstance();
        proxySubject.doSomething();}
}