一、cglib代理方式

public class UserService {
    public void login() {
        System.out.println("login...");
    }
    public void logout() {
        System.out.println("logout...");
    }
}

使用动态代理（不修改源码前提下）增强上面逻辑

    @Test
    public void cglibProxyTest() {
        UserService target = new UserService();
        // 通过cglib技术
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(UserService.class);
        // 增加增强逻辑
        enhancer.setCallbacks(new Callback[]{new MethodInterceptor() {
            //o:代理对象 methoProxy：代理方法
            //objects：方法入参
            @Override
            public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
                System.out.println("login before...");
                Object result = methodProxy.invoke(target, objects);
                //Object result = method.invoke(target, objects);
                System.out.println("login after...");
                return result;
            }
        },new MethodInterceptor() {
            @Override
            public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
                System.out.println("logout before...");
                Object result = methodProxy.invoke(target, objects);
                //Object result = method.invoke(target, objects);
                System.out.println("logout after...");
                return result;
            }
        }});
        enhancer.setCallbackFilter(new CallbackFilter() {
            @Override
            public int accept(Method method) {
                if (method.getName().equals("login"))
                    return 0;
                return 1;//数字对应new Callback[]数组索引
            }
        });
        // 生成UserService代理对象
        UserService userService = (UserService) enhancer.create();
        // 使用代理对象执行原有逻辑，就会执行增强逻辑
        userService.login();
        userService.loginout();
    }
login before...
login...
login after...
logout before...
logout...
logout after...

cglib是基于父子类机制，不依赖接口。被代理类时父类，新生成的代理类时子类。使用代理类生成代理对象。

二、JDK代理方式

此种代理方式，只能代理接口，利用接口产生jdk代理对象。

public interface ServiceInterface {
    void login();
    void logout();
}

    @Test
    public void jdkProxyTest(){
        UserService target = new UserService();
        ServiceInterface serviceInterface = (ServiceInterface)Proxy.newProxyInstance(UserService.class.getClassLoader(), new Class[]{ServiceInterface.class}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                System.out.println("before");
                return method.invoke(target,args);
            }
        });
        serviceInterface.login();
    }

三、Spring动态代理

Spring中对上面两种代理，进行了封装，封装出来的类叫做ProxyFactory（创建代理对象的一个工厂）

    @Test
    public void springProxyTest(){
        UserService target = new UserService();
        ProxyFactory proxyFactory = new ProxyFactory();
        proxyFactory.setTarget(target);
        proxyFactory.addAdvice(new org.aopalliance.intercept.MethodInterceptor() {
            @Override
            public Object invoke(MethodInvocation invocation) throws Throwable {
                System.out.println("before");
                Object proceed = invocation.proceed();
                System.out.println("after");
                return proceed;
            }
        });
        UserService userService = (UserService) proxyFactory.getProxy();
        userService.login();
    }

ProxyFactory底层会进行判断，如果UserService实现了接口，那么ProxyFactory底层就会用jdk动态代理，如果没有实现接口，就会用cglib技术。