【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：

java">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 overriding
    class 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

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getProxy
        return 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
    @Override
    public AopProxy createAopProxy(AdvisedSupport config) throws
            AopConfigException {
/**
 * 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 determine
                        target class: " +
                "Either an interface or a target is required for proxy
                creation.");
            }
            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
    @Override
    public 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
    @Override
    public 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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