【JavaEE进阶】 Spring AOP源码简单剖析

🍃前言

前面的博客中，博主对代理模式进行了一个简单的讲解，接下来博主将对Spring AOP源码进行简单剖析，使我们对Spring AOP了解的更加深刻。

🍀Spring AOP源码剖析

Spring AOP 主要基于两种⽅式实现的:JDK 及 CGLIB 的⽅式

Spring对于AOP的实现，基本上都是靠AnnotationAwareAspectJAutoProxyCreator 去完成⽣成代理对象的逻辑在⽗类 AbstractAutoProxyCreator 中

相关源码与注解如下：

protected Object createProxy(Class<?> beanClass, @Nullable String beanName,@Nullable Object[] specificInterceptors, TargetSource targetSource) {if (this.beanFactory instanceof ConfigurableListableBeanFactory) {AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory)this.beanFactory, beanName, beanClass);}
//创建代理⼯⼚ProxyFactory proxyFactory = new ProxyFactory();proxyFactory.copyFrom(this);
/*** 检查proxyTargetClass属性值，spring默认为false* proxyTargetClass 检查接⼝是否对类代理, ⽽不是对接⼝代理* 如果代理对象为类, 设置为true, 使⽤cglib代理*/if (!proxyFactory.isProxyTargetClass()) {
//是否有设置cglib代理if (shouldProxyTargetClass(beanClass, beanName)) {
//设置proxyTargetClass为true,使⽤cglib代理proxyFactory.setProxyTargetClass(true);} else {
/*** 如果beanClass实现了接⼝，且接⼝⾄少有⼀个⾃定义⽅法，则使⽤JDK代理* 否则CGLIB代理(设置ProxyTargetClass为true )* 即使我们配置了proxyTargetClass=false, 经过这⾥的⼀些判断还是可能会将其设为true*/evaluateProxyInterfaces(beanClass, proxyFactory);}}Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);proxyFactory.addAdvisors(advisors);proxyFactory.setTargetSource(targetSource);customizeProxyFactory(proxyFactory);proxyFactory.setFrozen(this.freezeProxy);if (advisorsPreFiltered()) {proxyFactory.setPreFiltered(true);}
// Use original ClassLoader if bean class not locally loaded in overridingclass loader
ClassLoader classLoader = getProxyClassLoader();if (classLoader instanceof SmartClassLoader && classLoader !=beanClass.getClassLoader()) {classLoader = ((SmartClassLoader) classLoader).getOriginalClassLoader();}
//从代理⼯⼚中获取代理return proxyFactory.getProxy(classLoader);
}

代理工⼚有⼀个重要的属性:proxyTargetClass,默认值为false.

也可以通过程序设置

proxyTargetClass	⽬标对象	代理⽅式
false	实现了接⼝	jdk代理
false	未实现接⼝(只有实现类)	cglib代理
true	实现了接⼝	cglib代理
true	未实现接⼝(只有实现类)	cglib代理

可以通过 @EnableAspectJAutoProxy(proxyTargetClass = true) 来设置

需要注意的是:

• Spring Boot 2.X开始,默认使⽤CGLIB代理，可以通过配置项 spring.aop.proxy-target-class=false 来进⾏修改,设置默认为jdk代理
  SpringBoot设置 @EnableAspectJAutoProxy ⽆效,因为Spring Boot默认使⽤AopAutoConfiguration进⾏装配

@SpringBootApplication
public class DemoApplication {public static void main(String[] args) {ApplicationContext context =SpringApplication.run(DemoApplication.class, args);
/*** HouseProxy houseProxy = context.getBean(HouseProxy.class);* 设置spring.aop.proxy-target-class=true cglib代理, 运⾏成功* 设置spring.aop.proxy-target-class=false jdk代理, 运⾏失败, 不能代理类* 因为 HouseProxy 是⼀个类, ⽽不是接⼝, 需要修改为* HouseSubject houseProxy = (HouseSubject)context.getBean("realHouseSubject")**/HouseProxy houseProxy = context.getBean(HouseProxy.class);
//HouseSubject houseProxy = (HouseSubject)context.getBean("realHouseSubject");//正确运⾏System.out.println(houseProxy.getClass().toString());}
}

注意：使⽤context.getBean()需要添加注解,使HouseProxy,RealHouseSubject被Spring管理测试AOP代理,需要把这些类交给AOP管理(⾃定义注解或使用@Aspect)

我们再看以下代理⼯⼚的代码

public class ProxyFactory extends ProxyCreatorSupport {//...代码省略
//获取代理public Object getProxy(@Nullable ClassLoader classLoader) {
//分两步 先createAopProxy,后getProxyreturn createAopProxy().getProxy(classLoader);}protected final synchronized AopProxy createAopProxy() {if (!this.active) {activate();}return getAopProxyFactory().createAopProxy(this);}
//...代码省略
}

createAopProxy的实现在DefaultAopProxyFactory中

public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {//...代码省略@Overridepublic AopProxy createAopProxy(AdvisedSupport config) throwsAopConfigException {
/*** 根据proxyTargetClass判断* 如果⽬标类是接⼝, 使⽤JDK动态代理* 否则使⽤cglib动态代理*/if (!NativeDetector.inNativeImage() &&(config.isOptimize() || config.isProxyTargetClass() ||hasNoUserSuppliedProxyInterfaces(config))) {Class<?> targetClass = config.getTargetClass();if (targetClass == null) {throw new AopConfigException("TargetSource cannot determinetarget class: " +"Either an interface or a target is required for proxycreation.");}if (targetClass.isInterface() || Proxy.isProxyClass(targetClass) ||ClassUtils.isLambdaClass(targetClass)) {return new JdkDynamicAopProxy(config);}return new ObjenesisCglibAopProxy(config);}else {return new JdkDynamicAopProxy(config);}}
//...代码省略
}

接下来就是创建代理了

JDK动态代理

final class JdkDynamicAopProxy implements AopProxy, InvocationHandler,Serializable {//...代码省略@Overridepublic Object getProxy(@Nullable ClassLoader classLoader) {if (logger.isTraceEnabled()) {logger.trace("Creating JDK dynamic proxy: " +this.advised.getTargetSource());}return Proxy.newProxyInstance(determineClassLoader(classLoader),this.proxiedInterfaces, this);}
//...代码省略
}

CGLIB动态代理

class CglibAopProxy implements AopProxy, Serializable {//...代码省略@Overridepublic Object getProxy(@Nullable ClassLoader classLoader) {//...代码省略
// Configure CGLIB Enhancer...Enhancer enhancer = createEnhancer();
// Generate the proxy class and create a proxy instance.return createProxyClassAndInstance(enhancer, callbacks);}
//...代码省略
}

以上就是对Spring AOP源码的一个简单剖析。

⭕总结

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