SpringAOP使用及源碼分析（SpringBoot下）

1、SpringAOP應用

1. 先搭建一個SpringBoot項目

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.1.7.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.mmc</groupId>
	<artifactId>springboot-study</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>springboot-study</name>
	<description>Demo project for Spring Boot</description>

	<properties>
		<java.version>1.8</java.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		
	</dependencies>
	
	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

2. 定義一個業務邏輯類，做爲切面

public interface CalculationService {

    /**
     * 加法運算
     * @param x
     * @param y
     * @return
     */
    public Integer add(Integer x,Integer y);
}

/**
 * @description:
 * @author: mmc
 * @create: 2020-06-01 14:22
 **/
@Service
public class CalculationServiceImpl implements CalculationService {

    @Override
    public Integer add(Integer x, Integer y) {
        if(x==null||y==null){
            throw  new NullPointerException("參數不能爲空");
        }
        return x+y;
    }
}

3. 定義一個切面類，添加通知方法

• 前置通知(@Before)：logStart：在目標方法(div)運行以前運行
• 後置通知(@After)：logEnd：在目標方法(add)運行結束以後運行（不管方法正常結束仍是異常結束）
• 返回通知(@AfterReturning)：logReturn：在目標方法(add)正常返回以後運行
• 異常通知(@AfterThrowing)：logException：在目標方法(add)出現異常之後運行
• 環繞通知(@Around)：動態代理，手動推動目標方法運行（joinPoint.procced()）

/**
 * @description:  切面類
 * @author: mmc
 * @create: 2020-06-01 14:24
 **/
@Aspect
@Component
public class LogAspects {

    //抽取公共的切入點表達式
    //一、本類引用
    //二、其餘的切面引用
    @Pointcut("execution(public Integer com.mmc.springbootstudy.service.CalculationService.*(..))")
    public void pointCut(){};

    @Before("pointCut()")
    public void logStart(JoinPoint joinPoint){
        Object[] args = joinPoint.getArgs();
        System.out.println(""+joinPoint.getSignature().getName()+"運行。。。@Before:參數列表是：{"+Arrays.asList(args)+"}");
    }

    @After("pointCut()")
    public void logEnd(JoinPoint joinPoint){
        System.out.println(""+joinPoint.getSignature().getName()+"結束。。。@After");
    }


    //JoinPoint必定要出如今參數表的第一位
    @AfterReturning(value="pointCut()",returning="result")
    public void logReturn(JoinPoint joinPoint,Object result){
        System.out.println(""+joinPoint.getSignature().getName()+"正常返回。。。@AfterReturning:運行結果：{"+result+"}");
    }

    @AfterThrowing(value="pointCut()",throwing="exception")
    public void logException(JoinPoint joinPoint,Exception exception){
        System.out.println(""+joinPoint.getSignature().getName()+"異常。。。異常信息：{"+exception+"}");
    }
}

4. 寫一個controller測試

@RequestMapping("/testaop")
   @ResponseBody
    public Integer testaop(Integer x,Integer y){
       Integer result = calculationService.add(x, y);
       return result;
   }

5. 測試

add運行。。。@Before:參數列表是：{[2, 3]}
add結束。。。@After
add正常返回。。。@AfterReturning:運行結果：{5}

2、源碼分析

主線流程圖：

---

1. spring.factories文件裏引入了AopAutoConfiguration類

@Configuration
@ConditionalOnClass({ EnableAspectJAutoProxy.class, Aspect.class, Advice.class, AnnotatedElement.class })
@ConditionalOnProperty(prefix = "spring.aop", name = "auto", havingValue = "true", matchIfMissing = true)
public class AopAutoConfiguration {

	@Configuration
	@EnableAspectJAutoProxy(proxyTargetClass = false)
	//看配置文件，若是配置的spring.aop.proxy-target-class爲false則引入JdkDynamicAutoProxyConfiguration
	@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "false",
			matchIfMissing = false)
	public static class JdkDynamicAutoProxyConfiguration {

	}

	@Configuration
	//開啓AspectJAutoProxy
	@EnableAspectJAutoProxy(proxyTargetClass = true)
	//看配置文件，若是配置的spring.aop.proxy-target-class爲true則引入CglibAutoProxyConfiguration 
	@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "true",
			matchIfMissing = true)
	public static class CglibAutoProxyConfiguration {

	}

}

在包目錄下找到配置文件，而且發現他的值爲true

在上面的方法上有EnableAspectJAutoProxy註解，並傳入了proxyTargetClass=true

2. 進入@EnableAspectJAutoProxy註解

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
//引入了AspectJAutoProxyRegistrar
@Import({AspectJAutoProxyRegistrar.class})
public @interface EnableAspectJAutoProxy {
    boolean proxyTargetClass() default false;

    boolean exposeProxy() default false;
}

3. 進入AspectJAutoProxyRegistrar類

class AspectJAutoProxyRegistrar implements ImportBeanDefinitionRegistrar {
    AspectJAutoProxyRegistrar() {
    }

    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        //註冊了自動自動代理類
        AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry);
        AnnotationAttributes enableAspectJAutoProxy = AnnotationConfigUtils.attributesFor(importingClassMetadata, EnableAspectJAutoProxy.class);
        if (enableAspectJAutoProxy != null) {
            if (enableAspectJAutoProxy.getBoolean("proxyTargetClass")) {
                AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
            }

            if (enableAspectJAutoProxy.getBoolean("exposeProxy")) {
                AopConfigUtils.forceAutoProxyCreatorToExposeProxy(registry);
            }
        }

    }
}

4. 進入registerAspectJAnnotationAutoProxyCreatorIfNecessary方法裏面

public static BeanDefinition registerAspectJAnnotationAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, @Nullable Object source) {
        return registerOrEscalateApcAsRequired(AnnotationAwareAspectJAutoProxyCreator.class, registry, source);
    }

能夠看到返回了一個BeanDefinition，裏面的BeanClass類型是AnnotationAwareAspectJAutoProxyCreator，這個類看名字是一個AOP的動態代理建立類，裏面沒有啥可疑的方法。在IDEA裏按Ctrl+H看他的繼承結構。有一個父類AbstractAutoProxyCreator，這個類實現了BeanPostProcessor接口。這個接口是Bean的擴展接口，在bean初始化完成後會調用到他的postProcessAfterInitialization(Object bean, String beanName)方法。

---

5. 方法內容以下

public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
        if (bean != null) {
            Object cacheKey = this.getCacheKey(bean.getClass(), beanName);
            if (this.earlyProxyReferences.remove(cacheKey) != bean) {
                //若是有必要，進行包裝  
                return this.wrapIfNecessary(bean, beanName, cacheKey);
            }
        }

        return bean;
    }
    
    protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
        if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
            return bean;
        } else if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
            return bean;
        } else if (!this.isInfrastructureClass(bean.getClass()) && !this.shouldSkip(bean.getClass(), beanName)) {
        //獲取切面的方法，第9點那裏展開討論
            Object[] specificInterceptors = this.getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, (TargetSource)null);
            if (specificInterceptors != DO_NOT_PROXY) {
                this.advisedBeans.put(cacheKey, Boolean.TRUE);
                //建立動態代理
                Object proxy = this.createProxy(bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
                this.proxyTypes.put(cacheKey, proxy.getClass());
                return proxy;
            } else {
                this.advisedBeans.put(cacheKey, Boolean.FALSE);
                return bean;
            }
        } else {
            this.advisedBeans.put(cacheKey, Boolean.FALSE);
            return bean;
        }
    }

6. 能夠看出這裏已經在開始建立動態代理了

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);
        }
        //動態代理工廠
        ProxyFactory proxyFactory = new ProxyFactory();
        proxyFactory.copyFrom(this);
        if (!proxyFactory.isProxyTargetClass()) {
            if (this.shouldProxyTargetClass(beanClass, beanName)) {
                proxyFactory.setProxyTargetClass(true);
            } else {
                this.evaluateProxyInterfaces(beanClass, proxyFactory);
            }
        }

        Advisor[] advisors = this.buildAdvisors(beanName, specificInterceptors);
        //切面那裏的方法
        proxyFactory.addAdvisors(advisors);
        proxyFactory.setTargetSource(targetSource);
        this.customizeProxyFactory(proxyFactory);
        proxyFactory.setFrozen(this.freezeProxy);
        if (this.advisorsPreFiltered()) {
            proxyFactory.setPreFiltered(true);
        }
        //獲取動態代理類
        return proxyFactory.getProxy(this.getProxyClassLoader());
    }

7. 學過AOP的人都知道動態代理的方式有兩種，一種JDK代理，一種CGLIB動態代理。那麼Spring裏面是怎麼選擇的呢？答案就在這裏：

public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
   // 1.config.isOptimize()是否使用優化的代理策略，目前使用與CGLIB
        // config.isProxyTargetClass() 是否目標類自己被代理而不是目標類的接口
        // hasNoUserSuppliedProxyInterfaces()是否存在代理接口

        if (!config.isOptimize() && !config.isProxyTargetClass() && !this.hasNoUserSuppliedProxyInterfaces(config)) {
            return new JdkDynamicAopProxy(config);
        } else {
            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.");
            } else {
                //目標類不是接口或不是代理類就使用cglib代理
                return (AopProxy)(!targetClass.isInterface() && !Proxy.isProxyClass(targetClass) ? new ObjenesisCglibAopProxy(config) : new JdkDynamicAopProxy(config));
            }
        }
    }

8. Cglib的代理類是CglibAopProxy、ObjenesisCglibAopProxy，JDK的代理類是JdkDynamicAopProxy。在這些類裏面對目標類進行了代理，在執行方法的時候就是執行的代理類的方法，而實現了切面編程的效果。
9. 主線流程就是這些了，還有一個沒說的就是咱們如何獲取的切面方法，@Before("pointCut()")這些註解又是如何生效的？再回到AbstractAutoProxyCreator的wrapIfNecessary()方法
   裏面有這句代碼：

Object[] specificInterceptors = this.getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, (TargetSource)null);
 
 
  @Nullable
    protected Object[] getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName, @Nullable TargetSource targetSource) {
        List<Advisor> advisors = this.findEligibleAdvisors(beanClass, beanName);
        return advisors.isEmpty() ? DO_NOT_PROXY : advisors.toArray();
    }
    
    protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
        //查找候選的要切面附加的方法，這裏加進去的
        List<Advisor> candidateAdvisors = this.findCandidateAdvisors();
        List<Advisor> eligibleAdvisors = this.findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
        this.extendAdvisors(eligibleAdvisors);
        if (!eligibleAdvisors.isEmpty()) {
            eligibleAdvisors = this.sortAdvisors(eligibleAdvisors);
        }

        return eligibleAdvisors;
    }

10. 他會找到Aspect類，而後遍歷裏面的方法，並獲取Pointcut，而後構造出Advisor，加入到集合List advisors裏，供動態代理時使用