【JavaEE进阶】 Spring AOP源码简单剖析

一时失言乱红尘 2024-04-17 10:50 141阅读 0赞

#### 文章目录 ####

*  ?前言
 *  ?Spring AOP源码剖析
 *  ⭕总结

## ?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 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

<table> 
 <thead> 
  <tr> 
   <th>proxyTargetClass</th> 
   <th>⽬标对象</th> 
   <th>代理⽅式</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>false</td> 
   <td>实现了接⼝</td> 
   <td>jdk代理</td> 
  </tr> 
  <tr> 
   <td>false</td> 
   <td>未实现接⼝(只有实现类)</td> 
   <td>cglib代理</td> 
  </tr> 
  <tr> 
   <td>true</td> 
   <td>实现了接⼝</td> 
   <td>cglib代理</td> 
  </tr> 
  <tr> 
   <td>true</td> 
   <td>未实现接⼝(只有实现类)</td> 
   <td>cglib代理</td> 
  </tr> 
 </tbody> 
</table>

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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