为什么JDK动态代理仅适用于接口？ [英] Why does JDK dynamic Proxy only work with Interfaces?

问题描述

JDK Proxy类仅接受工厂方法newProxyInstance（）中的接口。

The JDK Proxy class only accepts interfaces in the factory method newProxyInstance().

是否有可用的解决方法或替代实施？
如果我必须将方法提取到接口以便使它们与代理一起使用，则用例是有限的。我想将它们包装起来以在运行时应用基于注释的操作。

Is there a workaround available, or alternative implementations? The use cases are limited if I have to extract methods to an interface in order to enable them for use with a proxy. I would like to wrap them to apply annotation based actions during runtime.

public static <T> T getProxy(T obj) {
   InvocationHandler ih = new InjectProxy( obj );
   ClassLoader classLoader = InjectProxy.class.getClassLoader();
   return (T) Proxy.newProxyInstance( classLoader, obj.getClass().getInterfaces(), ih );
                                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^  
}

推荐答案

你可以像这样使用cglib：

You can use cglib like this:

import java.lang.reflect.Array;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;


public class AbstractFactory {

    @SuppressWarnings("unchecked")
    public static <A> A createDefaultImplementation(Class<A> abstractClass) {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(abstractClass);
        enhancer.setCallback(new MethodInterceptor() {
            public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
                if (!Modifier.isAbstract(method.getModifiers())) {
                    return methodProxy.invokeSuper(proxy, args);
                } else {
                    Class type = method.getReturnType();
                    if (type.isPrimitive() && !void.class.equals(type)) {
                        return Array.get(Array.newInstance(type, 1), 0);
                    } else {
                        return null;
                    }
                }
            }
        });
        return (A) enhancer.create();
    }

    @SuppressWarnings("unchecked")
    public static <A> A createDefaultImplementation(String className) throws ClassNotFoundException{
        return (A) createDefaultImplementation(Class.forName(className));
    }
}

例如，这允许您使用默认值构建抽象类实施方法。但是你可以将增强器改为你想要的。

This for example lets you build abstract classes with a default implementation method. But you can change the enhancer to what ever you want.

这篇关于为什么JDK动态代理仅适用于接口？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！