Spring AOP源码剖析

Posted 2021-07-29 怀瑾Hello World

Spring AOP源码剖析

• 1.代理对象创建
• • 1.1.AOP基础⽤例准备
  • 1.2.时机点分析
  • 1.3.代理对象创建流程
• 2.Spring声明式事务控制
• • 2.1.@EnableTransactionManagement
  • 2.2.加载事务控制组件
• 3.注意事项

1.代理对象创建

1.1.AOP基础⽤例准备

• Bean定义

package aop;

import org.springframework.stereotype.Component;

@Component
public class LagouBeanAop {
	public void tech(){
		System.out.println("java learning......");
	}
}

• Aspect定义

package aop;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.*;
import org.springframework.stereotype.Component;

@Component
@Aspect
public class LagouAspect {

	@Pointcut("execution(* aop.LagouBeanAop.tech())")
	public void pointcut() {
	}

	@Before("pointcut()")
	public void before() {
		System.out.println("before method ......");
	}

	@After("pointcut()")
	public void after() {
		System.out.println("after method ......");
	}

	@AfterReturning("pointcut()")
	public void afterReturn() {
		System.out.println("after return method ......");
	}

	@AfterThrowing("pointcut()")
	public void afterThrow() {
		System.out.println("after throw method ......");
	}


	@Around("pointcut()")
	public void around(ProceedingJoinPoint joinPoint) throws Throwable {
		System.out.println("around method before tagert method......");
		joinPoint.proceed(joinPoint.getArgs());
		System.out.println("around method after tagert method......");
	}
}

• SpringConfiguration

package aop;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.EnableAspectJAutoProxy;

@Configuration
@ComponentScan("aop")
@EnableAspectJAutoProxy //开启spring对注解AOP的⽀持
public class SpringConfiguration {

}

• 测试用例

	/**
	 * 测试⽤例：Aop 代理对象创建
	 */
	@Test
	public void testAopProxyBuild(){
		ApplicationContext applicationContext = new
				AnnotationConfigApplicationContext(SpringConfiguration.class);
		LagouBeanAop lagouBeanAop = applicationContext.getBean(LagouBeanAop.class);
		lagouBeanAop.tech();
	}

1.2.时机点分析

• 我们发现在 getBean 之前，LagouBean对象已经产⽣（即在第⼀⾏初始化代码中完成），⽽且该对象是⼀个代理对象（Cglib代理对象），我们断定，容器初始化过程中⽬标Ban已经完成了代理，返回了代理对象。

1.3.代理对象创建流程

• AbstractAutowireCapableBeanFactory#initializeBean(java.lang.String,java.lang.Object, org.springframework.beans.factory.support.RootBeanDefinition)

	/**
	 * Initialize the given bean instance, applying factory callbacks
	 * as well as init methods and bean post processors.
	 * <p>Called from {@link #createBean} for traditionally defined beans,
	 * and from {@link #initializeBean} for existing bean instances.
	 * @param beanName the bean name in the factory (for debugging purposes)
	 * @param bean the new bean instance we may need to initialize
	 * @param mbd the bean definition that the bean was created with
	 * (can also be {@code null}, if given an existing bean instance)
	 * @return the initialized bean instance (potentially wrapped)
	 * @see BeanNameAware
	 * @see BeanClassLoaderAware
	 * @see BeanFactoryAware
	 * @see #applyBeanPostProcessorsBeforeInitialization
	 * @see #invokeInitMethods
	 * @see #applyBeanPostProcessorsAfterInitialization
	 */
	protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
		if (System.getSecurityManager() != null) {
			AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
				invokeAwareMethods(beanName, bean);
				return null;
			}, getAccessControlContext());
		}
		else {
			invokeAwareMethods(beanName, bean);
		}

		Object wrappedBean = bean;
		if (mbd == null || !mbd.isSynthetic()) {
			// 执⾏所有的BeanPostProcessor#postProcessBeforeInitialization 初始化之前的处理器⽅法
			wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
		}

		try {
			// 这⾥就开始执⾏afterPropertiesSet（实现了InitializingBean接⼝）⽅法和initMethod
			invokeInitMethods(beanName, wrappedBean, mbd);
		}
		catch (Throwable ex) {
			throw new BeanCreationException(
					(mbd != null ? mbd.getResourceDescription() : null),
					beanName, "Invocation of init method failed", ex);
		}
		if (mbd == null || !mbd.isSynthetic()) {
			// 整个Bean初始化完成，执⾏后置处理器⽅法
			wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
		}

		return wrappedBean;
	}

• AbstractAutowireCapableBeanFactory#applyBeanPostProcessorsAfterInitialization

	@Override
	public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
			throws BeansException {

		Object result = existingBean;
		// 循环后置处理器
		for (BeanPostProcessor processor : getBeanPostProcessors()) {
			Object current = processor.postProcessAfterInitialization(result, beanName);
			if (current == null) {
				return result;
			}
			result = current;
		}
		return result;
	}

• 创建代理对象的后置处理AbstractAutoProxyCreator#postProcessAfterInitialization

	/**
	 * Create a proxy with the configured interceptors if the bean is
	 * identified as one to proxy by the subclass.
	 * @see #getAdvicesAndAdvisorsForBean
	 */
	@Override
	public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
		if (bean != null) {
		// 检查下该类是否已经暴露过了（可能已经创建了，⽐如A依赖B时，创建A时候，就先去创建B。
		// 当真正需要创建B时，就没必要再代理⼀次已经代理过的对象）,避免重复创建
			Object cacheKey = getCacheKey(bean.getClass(), beanName);
			if (this.earlyProxyReferences.remove(cacheKey) != bean) {
				return wrapIfNecessary(bean, beanName, cacheKey);
			}
		}
		return bean;
	}

• AbstractAutoProxyCreator#wrapIfNecessary

	/**
	 * Wrap the given bean if necessary, i.e. if it is eligible for being proxied.
	 * @param bean the raw bean instance
	 * @param beanName the name of the bean
	 * @param cacheKey the cache key for metadata access
	 * @return a proxy wrapping the bean, or the raw bean instance as-is
	 */
	protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
		// targetSourcedBeans包含，说明前⾯创建过
		if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
			return bean;
		}
		if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
			return bean;
		}
		if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
			this.advisedBeans.put(cacheKey, Boolean.FALSE);
			return bean;
		}

		// Create proxy if we have advice.
		// 得到所有候选Advisor，对Advisors和bean的⽅法双层遍历匹配，最终得到⼀个List<Advisor>，即specificInterceptors
		Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
		if (specificInterceptors != DO_NOT_PROXY) {
			this.advisedBeans.put(cacheKey, Boolean.TRUE);
			// 重点，创建代理对象
			Object proxy = createProxy(
					bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
			this.proxyTypes.put(cacheKey, proxy.getClass());
			return proxy;
		}

		this.advisedBeans.put(cacheKey, Boolean.FALSE);
		return bean;
	}

• specificInterceptors ：得到所有候选Advisor，对Advisors和bean的⽅法双层遍历匹配，最终得到⼀个List<Advisor>
  
• AbstractAutoProxyCreator#createProxy

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);
		}

		// 创建代理的⼯作交给ProxyFactory
		ProxyFactory proxyFactory = new ProxyFactory();
		proxyFactory.copyFrom(this);

		// 根据⼀些情况判断是否要设置proxyTargetClass=true
		if (!proxyFactory.isProxyTargetClass()) {
			if (shouldProxyTargetClass(beanClass, beanName)) {
				proxyFactory.setProxyTargetClass(true);
			}
			else {
				evaluateProxyInterfaces(beanClass, proxyFactory);
			}
		}

		// 把指定和通⽤拦截对象合并, 并都适配成Advisor
		Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
		// 设置参数
		proxyFactory.addAdvisors(advisors);
		proxyFactory.setTargetSource(targetSource);
		customizeProxyFactory(proxyFactory);

		proxyFactory.setFrozen(this.freezeProxy);
		if (advisorsPreFiltered()) {
			proxyFactory.setPreFiltered(true);
		}

		// 上⾯准备做完就开始创建代理
		return proxyFactory.getProxy(getProxyClassLoader());
	}

• 接着跟进到ProxyFactory中

	/**
	 * Create a new proxy according to the settings in this factory.
	 * <p>Can be called repeatedly. Effect will vary if we've added
	 * or removed interfaces. Can add and remove interceptors.
	 * <p>Uses the given class loader (if necessary for proxy creation).
	 * @param classLoader the class loader to create the proxy with
	 * (or {@code null} for the low-level proxy facility's default)
	 * @return the proxy object
	 */
	public Object getProxy(@Nullable ClassLoader classLoader) {
	// ⽤ProxyFactory创建AopProxy, 然后⽤AopProxy创建Proxy, 所以这⾥重要的是看获取的AopProxy对象是什么,
	// 然后进去看怎么创建动态代理, 提供了两种：jdk proxy, cglib
		return createAopProxy().getProxy(classLoader);
	}

public class ProxyCreatorSupport extends AdvisedSupport {

	private AopProxyFactory aopProxyFactory;
	
	public ProxyCreatorSupport() {
		this.aopProxyFactory = new DefaultAopProxyFactory();
	}
	
	protected final synchronized AopProxy createAopProxy() {
		if (!this.active) {
			activate();
		}
		//先获取创建AopProxy的⼯⼚, 再由此创建AopProxy
		return getAopProxyFactory().createAopProxy(this);
	}
	
	public AopProxyFactory getAopProxyFactory() {
		return this.aopProxyFactory;
	}
}

• 流程就是⽤AopProxyFactory创建AopProxy, 再⽤AopProxy创建代理对象，这⾥的AopProxyFactory默认是DefaultAopProxyFactory，看他的createAopProxy⽅法

public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {

	@Override
	public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
		if (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)) {
				return new JdkDynamicAopProxy(config);
			}
			return new ObjenesisCglibAopProxy(config);
		}
		else {
			return new JdkDynamicAopProxy(config);
		}
	}

	/**
	 * Determine whether the supplied {@link AdvisedSupport} has only the
	 * {@link org.springframework.aop.SpringProxy} interface specified
	 * (or no proxy interfaces specified at all).
	 */
	private boolean hasNoUserSuppliedProxyInterfaces(AdvisedSupport config) {
		Class<?>[] ifcs = config.getProxiedInterfaces();
		return (ifcs.length == 0 || (ifcs.length == 1 && SpringProxy.class.isAssignableFrom(ifcs[0])));
	}

}

• 这⾥决定创建代理对象是⽤JDK Proxy，还是⽤ Cglib 了，最简单的从使⽤⽅⾯使⽤来说：设置proxyTargetClass=true强制使⽤Cglib 代理，什么参数都不设并且对象类实现了接⼝则默认⽤JDK 代理，如果没有实现接⼝则也必须⽤CglibProxyFactory#getProxy(java.lang.ClassLoader)
  ------ CglibAopProxy#getProxy(java.lang.ClassLoader)

	@Override
	public Object getProxy(@Nullable ClassLoader classLoader) {
		if (logger.isTraceEnabled()) {
			logger.trace("Creating CGLIB proxy: " + this.advised.getTargetSource());
		}

		try {
			Class<?> rootClass = this.advised.getTargetClass();
			Assert.state(rootClass != null, "Target class must be available for creating a CGLIB proxy");

			Class<?> proxySuperClass = rootClass;
			if (ClassUtils.isCglibProxyClass(rootClass)) {
				proxySuperClass = rootClass.getSuperclass();
				Class<?>[] additionalInterfaces = rootClass.getInterfaces();
				for (Class<?> additionalInterface : additionalInterfaces) {
					this.advised.addInterface(additionalInterface);
				}
			}

			// Validate the class, writing log messages as necessary.
			validateClassIfNecessary(proxySuperClass, classLoader);

			// 配置 Cglib 增强
			Enhancer enhancer = createEnhancer();
			if (classLoader != null) {
				enhancer.setClassLoader(classLoader);
				if (classLoader instanceof SmartClassLoader &&
						((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {
					enhancer.setUseCache(false);
				}
			}
			enhancer.setSuperclass(proxySuperClass);
			enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
			enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
			enhancer.setStrategy(new ClassLoaderAwareUndeclaredThrowableStrategy(classLoader));

			Callback[] callbacks = getCallbacks(rootClass);
			Class<?>[] types = new Class<?>[callbacks.length];
			for (int x = 0; x < types.length; x++) {
				types[x] = callbacks[x].getClass();
			}
			// fixedInterceptorMap only populated at this point, after getCallbacks call above
			enhancer.setCallbackFilter(new ProxyCallbackFilter(
					this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));
			enhancer.setCallbackTypes(types);

			// ⽣成代理类，并且创建⼀个代理类的实例
			return createProxyClassAndInstance(enhancer, callbacks);
		}
		catch (CodeGenerationException | IllegalArgumentException ex) {
			throw new AopConfigException("Could not generate CGLIB subclass of " + this.advised.getTargetClass() +
					": Common causes of this problem include using a final class or a non-visible class",
					ex);
		}
		catch (Throwable ex) {
			// TargetSource.getTarget() failed
			throw new AopConfigException("Unexpected AOP exception", ex);
		}
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