代理模式和装饰器模式一样，都是在不修改原始类的情况下，增强功能。代理模式的侧重点在于扩展功能，装饰器的侧重点在于多个功能组合使用。

通过不同的代理模式，实现这样一个需求：通过代理类对 api 接口做鉴权判断，并能应用到多个接口上。

静态代理

public interface Controller {

    void request(String param);

}

public class UserController implements Controller {

    @Override
    public void request(String param) {
        System.out.println("request user api: " + param);
    }
}

public class AuthorityControllerProxy implements Controller {

    private final Controller target;

    public AuthorityControllerProxy(final Controller target) {
        this.target = target;
    }

    @Override
    public void request(final String param) {
        if (!"admin".equals(param)) {
            System.out.println("401");
            return;
        }
        target.request(param);
    }
}

测试类

public class WebApp {

    public static void main(String[] args) {
        Controller controller = new AuthorityControllerProxy(new UserController());
        controller.request("user");
        controller.request("admin");
    }
}

动态代理

JDK 实现

public interface Controller {

    void request(String param);

}

public class UserController implements Controller {

    @Override
    public void request(String param) {
        System.out.println("request user api: " + param);
    }
}

// 创建代理对象工具类
public class JdkProxyKit {

    public static <T> T newProxyInstance(Object obj, InvocationHandler handler) {
        final ClassLoader classLoader = obj.getClass().getClassLoader();
        final Class<?>[] interfaces = obj.getClass().getInterfaces();
        final Object instance = Proxy.newProxyInstance(classLoader, interfaces, handler);
        return (T) instance;
    }
}

// 扩展代理类功能
public class AuthorityControllerJdkProxy implements InvocationHandler {

    private final Controller target;

    public AuthorityControllerJdkProxy(final Controller target) {
        this.target = target;
    }

    @Override
    public Object invoke(final Object proxy, final Method method, final Object[] args) throws Throwable {
        if (args == null || args.length < 1) {
            System.out.println("401");
            return null;
        }
        String param = (String) args[0];
        if (!"admin".equals(param)) {
            System.out.println("401");
            return null;
        }
        return method.invoke(target, args);
    }
}

测试类

public class JdkProxyApp {

    public static void main(String[] args) {
        Controller controller = new UserController();
        final AuthorityControllerJdkProxy handler = new AuthorityControllerJdkProxy(controller);
        final Controller proxyController = JdkProxyKit.newProxyInstance(controller, handler);
        System.out.println(proxyController.getClass().getName());
        proxyController.request("user");
        proxyController.request("admin");
    }
}

cglib 实现

public class AdminController {

    public void request(String param) {
        System.out.println("request admin api: " + param);
    }
}

public class AuthorityControllerCglibProxy implements MethodInterceptor {


    private final Object target;

    public AuthorityControllerCglibProxy(final Object target) {
        this.target = target;
    }

    @Override
    public Object intercept(final Object obj, final Method method, final Object[] args, final MethodProxy proxy) throws Throwable {
        if (args == null || args.length < 1) {
            System.out.println("401");
            return null;
        }
        String param = (String) args[0];
        if (!"admin".equals(param)) {
            System.out.println("401");
            return null;
        }
        return method.invoke(target, args);
    }
}

public class CglibProxyKit {

    @SuppressWarnings("unchecked")
    public static <T> T newProxyInstance(T target, MethodInterceptor interceptor) {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(target.getClass());
        enhancer.setCallback(interceptor);
        return (T) enhancer.create();
    }
}

测试类

public class CglibProxyApp {

    public static void main(String[] args) {
        AdminController controller = new AdminController();
        final AuthorityControllerCglibProxy proxy = new AuthorityControllerCglibProxy(controller);
        final AdminController proxyController = CglibProxyKit.newProxyInstance(controller, proxy);
        proxyController.request("user");
        proxyController.request("admin");
    }
}

其他 cglib 用法：https://github.com/cglib/cglib (opens new window)

bytebuddy 实现

public class AdminController {

    public void request(String param) {
        System.out.println("request admin api: " + param);
    }
}

public class AuthorityControllerByteBuddyProxy {

    private final AdminController target;

    public AuthorityControllerByteBuddyProxy(final AdminController target) {
        this.target = target;
    }

    public void request(String param) {
        if (!"admin".equals(param)) {
            System.out.println("401");
            return;
        }
        target.request(param);
    }
}

public class ByteBuddyProxyKit {

    @SuppressWarnings({"resource", "unchecked"})
    public static <T> T newProxyInstance(Class<T> targetClass, String methodName, Object delegate)
            throws InstantiationException, IllegalAccessException {
        Class<?> dynamicType = new ByteBuddy()
                .subclass(targetClass)
                .method(ElementMatchers.named(methodName))
                .intercept(MethodDelegation.to(delegate))
                .make()
                .load(targetClass.getClassLoader())
                .getLoaded();
        return (T) dynamicType.newInstance();
    }
}

测试类

public class ByteBuddyProxyApp {

    public static void main(String[] args) throws InstantiationException, IllegalAccessException {
        AdminController controller = new AdminController();
        AuthorityControllerByteBuddyProxy proxy = new AuthorityControllerByteBuddyProxy(controller);
        final AdminController proxyController = ByteBuddyProxyKit.newProxyInstance(AdminController.class, "request", proxy);
        proxyController.request("user");
        proxyController.request("admin");
    }
}

其他 bytebuddy 用法：https://github.com/raphw/byte-buddy (opens new window)