jdk 和 cglib 在 Spring 中的统一

Spring AOP抽象

• 切点：接口 Pointcut，典型实现 AspectJExpressionPointcut

• 通知：典型接口为 MethodInterceptor 代表环绕通知

• 切面：Advisor，包含一个 Advice 通知，PointcutAdvisor 包含一个 Advice 通知和一个 Pointcut

classDiagram

class Advice
class MethodInterceptor
class Advisor
class PointcutAdvisor

Pointcut <|-- AspectJExpressionPointcut
Advice <|-- MethodInterceptor
Advisor <|-- PointcutAdvisor
PointcutAdvisor o-- "一" Pointcut
PointcutAdvisor o-- "一" Advice

<<interface>> Advice
<<interface>> MethodInterceptor
<<interface>> Pointcut
<<interface>> Advisor
<<interface>> PointcutAdvisor

Spring AOP cglib和jdk代理的选择

• AopProxyFactory 根据 proxyTargetClass 等设置选择 AopProxy 实现

• AopProxy 通过 getProxy 创建代理对象

• 图中 Proxy 都实现了 Advised 接口，能够获得关联的切面集合与目标（其实是从 ProxyFactory 取得）

• 调用代理方法时，会借助 ProxyFactory 将通知统一转为环绕通知：MethodInterceptor

classDiagram

Advised <|-- ProxyFactory
ProxyFactory o-- Target
ProxyFactory o-- "多" Advisor

ProxyFactory --> AopProxyFactory : 使用
AopProxyFactory --> AopProxy
Advised <|-- 基于CGLIB的Proxy
基于CGLIB的Proxy <-- ObjenesisCglibAopProxy : 创建
AopProxy <|-- ObjenesisCglibAopProxy
AopProxy <|-- JdkDynamicAopProxy
基于JDK的Proxy <-- JdkDynamicAopProxy : 创建
Advised <|-- 基于JDK的Proxy

class AopProxy {
   +getProxy() Object
}

class ProxyFactory {
	proxyTargetClass : boolean
}

class ObjenesisCglibAopProxy {
	advised : ProxyFactory
}

class JdkDynamicAopProxy {
	advised : ProxyFactory
}

<<interface>> Advised
<<interface>> AopProxyFactory
<<interface>> AopProxy

proxyTargetClass = false, 目标实现了接口, 用 jdk 实现

public class A15 {
    public static void main(String[] args) {
        /*
            两个切面概念
            aspect =
                通知1(advice) +  切点1(pointcut)
                通知2(advice) +  切点2(pointcut)
                通知3(advice) +  切点3(pointcut)
                ...
            advisor = 更细粒度的切面，包含一个通知和切点
         */

        // 1. 备好切点
        AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut();
        pointcut.setExpression("execution(* foo())");
        // 2. 备好通知
        MethodInterceptor advice = invocation -> {
            System.out.println("before...");
            Object result = invocation.proceed(); // 调用目标
            System.out.println("after...");
            return result;
        };
        // 3. 备好切面
        DefaultPointcutAdvisor advisor = new DefaultPointcutAdvisor(pointcut, advice);

        /*
           4. 创建代理
                a. proxyTargetClass = false, 目标实现了接口, 用 jdk 实现
                b. proxyTargetClass = false,  目标没有实现接口, 用 cglib 实现
                c. proxyTargetClass = true, 总是使用 cglib 实现
         */
        Target2 target = new Target2();
        ProxyFactory factory = new ProxyFactory();
        factory.setTarget(target);
        factory.addAdvisor(advisor);
        factory.setInterfaces(target.getClass().getInterfaces());
        factory.setProxyTargetClass(false);
        Target2 proxy = (Target2) factory.getProxy();
        System.out.println(proxy.getClass());
        proxy.foo();
        proxy.bar();
        /*
            学到了什么
                a. Spring 的代理选择规则
                b. 底层的切点实现
                c. 底层的通知实现
                d. ProxyFactory 是用来创建代理的核心实现, 用 AopProxyFactory 选择具体代理实现
                    - JdkDynamicAopProxy
                    - ObjenesisCglibAopProxy
         */
    }

    interface I1 {
        void foo();

        void bar();
    }

    static class Target1 implements I1 {
        public void foo() {
            System.out.println("target1 foo");
        }

        public void bar() {
            System.out.println("target1 bar");
        }
    }

    static class Target2 {
        public void foo() {
            System.out.println("target2 foo");
        }

        public void bar() {
            System.out.println("target2 bar");
        }
    }
}

proxyTargetClass = true, 总是使用 cglib 实现

Target1 target = new Target1();
        ProxyFactory factory = new ProxyFactory();
        factory.setTarget(target);
        factory.addAdvisor(advisor);
        factory.setInterfaces(target.getClass().getInterfaces());
        factory.setProxyTargetClass(true);
        I1 proxy = (I1) factory.getProxy();
        System.out.println(proxy.getClass());
        proxy.foo();
        proxy.bar();

class com.onethink.a15.A15$Target1$$EnhancerBySpringCGLIB$$9fe985e9
before...
target1 foo
after...
target1 bar

proxyTargetClass = false, 目标没有实现接口, 用 cglib 实现

Target2 target = new Target2();
        ProxyFactory factory = new ProxyFactory();
        factory.setTarget(target);
        factory.addAdvisor(advisor);
        factory.setInterfaces(target.getClass().getInterfaces());
        factory.setProxyTargetClass(false);
        Target2 proxy = (Target2) factory.getProxy();
        System.out.println(proxy.getClass());
        proxy.foo();
        proxy.bar();

class com.onethink.a15.A15$Target2$$EnhancerBySpringCGLIB$$e581ba21
before...
target2 foo
after...
target2 bar