spring tx @Transactional 详解 `Advisor`、`Target`、`ProxyFactory

在Spring中，@Transactional注解的处理涉及到多个关键组件，包括Advisor、Target、ProxyFactory等。下面是详细的解析和代码示例，解释这些组件是如何协同工作的。

1. 关键组件介绍

1.1 Advisor

Advisor是一个Spring AOP的概念，它包含了切点（Pointcut）和通知（Advice）。在事务管理中，TransactionAttributeSourceAdvisor是一个典型的Advisor。

1.2 Target

Target是指被代理的目标对象，即实际执行业务逻辑的对象。

1.3 ProxyFactory

ProxyFactory是Spring提供的用于创建代理对象的工厂类。它可以使用JDK动态代理或CGLIB创建代理对象。

2. @Transactional的处理流程

解析注解：Spring扫描@Transactional注解。
创建Advisor：创建包含事务处理逻辑的Advisor。
创建代理对象：使用ProxyFactory为目标对象创建代理对象，并将Advisor加入到代理对象中。

3. 代码示例

3.1 配置类

首先，通过@EnableTransactionManagement启用事务管理。

import org.springframework.context.annotation.Configuration;
import org.springframework.transaction.annotation.EnableTransactionManagement;@Configuration
@EnableTransactionManagement
public class AppConfig {// DataSource, EntityManagerFactory, TransactionManager beans configuration
}

3.2 目标对象和接口

定义一个业务接口和其实现类：

public interface MyService {void myTransactionalMethod();
}@Service
public class MyServiceImpl implements MyService {@Override@Transactionalpublic void myTransactionalMethod() {// 业务逻辑System.out.println("Executing myTransactionalMethod");}
}

3.3 ProxyFactory和Advisor

使用ProxyFactory和TransactionAttributeSourceAdvisor来创建代理对象并处理事务：

import org.springframework.aop.framework.ProxyFactory;
import org.springframework.aop.support.DefaultPointcutAdvisor;
import org.springframework.transaction.interceptor.TransactionInterceptor;
import org.springframework.transaction.interceptor.TransactionAttributeSource;
import org.springframework.transaction.interceptor.NameMatchTransactionAttributeSource;public class ProxyFactoryExample {public static void main(String[] args) {// 创建目标对象MyService target = new MyServiceImpl();// 创建事务属性源TransactionAttributeSource transactionAttributeSource = new NameMatchTransactionAttributeSource();// 创建事务拦截器TransactionInterceptor transactionInterceptor = new TransactionInterceptor();transactionInterceptor.setTransactionAttributeSource(transactionAttributeSource);// 创建AdvisorDefaultPointcutAdvisor advisor = new DefaultPointcutAdvisor();advisor.setAdvice(transactionInterceptor);// 创建ProxyFactoryProxyFactory proxyFactory = new ProxyFactory();proxyFactory.setTarget(target);proxyFactory.addAdvisor(advisor);// 创建代理对象MyService proxy = (MyService) proxyFactory.getProxy();// 调用代理对象的方法proxy.myTransactionalMethod();}
}

4. 详细解释

4.1 创建目标对象

MyService target = new MyServiceImpl();

这是被代理的目标对象，它包含了业务逻辑，并使用了@Transactional注解。

4.2 创建事务属性源

TransactionAttributeSource transactionAttributeSource = new NameMatchTransactionAttributeSource();

TransactionAttributeSource用于解析事务属性。NameMatchTransactionAttributeSource是一个实现类，可以基于方法名称匹配事务属性。

4.3 创建事务拦截器

TransactionInterceptor transactionInterceptor = new TransactionInterceptor();
transactionInterceptor.setTransactionAttributeSource(transactionAttributeSource);

TransactionInterceptor实现了MethodInterceptor接口，用于在方法调用前后处理事务逻辑。

4.4 创建Advisor

DefaultPointcutAdvisor advisor = new DefaultPointcutAdvisor();
advisor.setAdvice(transactionInterceptor);

DefaultPointcutAdvisor包含了事务拦截器，可以在匹配的方法上应用事务逻辑。

4.5 创建ProxyFactory

ProxyFactory proxyFactory = new ProxyFactory();
proxyFactory.setTarget(target);
proxyFactory.addAdvisor(advisor);

ProxyFactory用于创建代理对象。它将目标对象和Advisor结合起来，生成代理对象。

4.6 创建代理对象并调用方法

MyService proxy = (MyService) proxyFactory.getProxy();
proxy.myTransactionalMethod();

通过ProxyFactory.getProxy()方法创建代理对象，并调用代理对象的方法。这时，事务拦截器会在方法调用前后执行事务处理逻辑。

5. 总结

通过以上代码示例，可以看出Spring如何解析@Transactional注解，并使用Advisor、Target和ProxyFactory创建代理对象来处理事务逻辑。这些组件协同工作，实现了自动的事务管理。

proxyFactory源码

targetSource与代理对象是两个对象，
在调用代理对象的时候，实际上是要被DynamicAdvisedInterceptor拦截，之后在拦截方法中执行执行拦截器调用链，并把targetSource传给拦截器。
相当于把targetSource对象（非类）作为成员变量传递给代理对象，然后对targetSource对象的方法调用增强。
类->BeanDefinition->bean初始化->为bean添加后置处理器，替换bean对象为proxy对象，其中bean对象作为代理对象的成员变量targetSource，代理对象通过在拦截方法中对targetSource对象的方法调用前后执行advisor的方法。

对比 @Configuration对@bean方法的处理，是直接生成子类，子类重写@bean方法，子类作为BeanDefinition替换原始@Configuration注解的类，因此在子类中的this调用就是对子类重写的方法调用。

//CglibAopProxy
/*** General purpose AOP callback. Used when the target is dynamic or when the* proxy is not frozen.*/private static class DynamicAdvisedInterceptor implements MethodInterceptor, Serializable {private final AdvisedSupport advised;public DynamicAdvisedInterceptor(AdvisedSupport advised) {this.advised = advised;}@Override@Nullablepublic Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {Object oldProxy = null;boolean setProxyContext = false;Object target = null;TargetSource targetSource = this.advised.getTargetSource();try {if (this.advised.exposeProxy) {// Make invocation available if necessary.oldProxy = AopContext.setCurrentProxy(proxy);setProxyContext = true;}// Get as late as possible to minimize the time we "own" the target, in case it comes from a pool...target = targetSource.getTarget();Class<?> targetClass = (target != null ? target.getClass() : null);List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);Object retVal;// Check whether we only have one InvokerInterceptor: that is,// no real advice, but just reflective invocation of the target.if (chain.isEmpty() && CglibMethodInvocation.isMethodProxyCompatible(method)) {// We can skip creating a MethodInvocation: just invoke the target directly.// Note that the final invoker must be an InvokerInterceptor, so we know// it does nothing but a reflective operation on the target, and no hot// swapping or fancy proxying.Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);retVal = invokeMethod(target, method, argsToUse, methodProxy);}else {// We need to create a method invocation...// 链式调用retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();}retVal = processReturnType(proxy, target, method, retVal);return retVal;}finally {if (target != null && !targetSource.isStatic()) {targetSource.releaseTarget(target);}if (setProxyContext) {// Restore old proxy.AopContext.setCurrentProxy(oldProxy);}}}@Overridepublic boolean equals(@Nullable Object other) {return (this == other ||(other instanceof DynamicAdvisedInterceptor &&this.advised.equals(((DynamicAdvisedInterceptor) other).advised)));}/*** CGLIB uses this to drive proxy creation.*/@Overridepublic int hashCode() {return this.advised.hashCode();}}

//ReflectiveMethodInvocation
@Override@Nullablepublic Object proceed() throws Throwable {// We start with an index of -1 and increment early.if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {return invokeJoinpoint();}Object interceptorOrInterceptionAdvice =this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {// Evaluate dynamic method matcher here: static part will already have// been evaluated and found to match.InterceptorAndDynamicMethodMatcher dm =(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;Class<?> targetClass = (this.targetClass != null ? this.targetClass : this.method.getDeclaringClass());if (dm.methodMatcher.matches(this.method, targetClass, this.arguments)) {return dm.interceptor.invoke(this);}else {// Dynamic matching failed.// Skip this interceptor and invoke the next in the chain.return proceed();}}else {// It's an interceptor, so we just invoke it: The pointcut will have// been evaluated statically before this object was constructed.//调用 @Transactional事务拦截器return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);}}

//TransactionInterceptor@Nullablepublic Object invoke(MethodInvocation invocation) throws Throwable {Class<?> targetClass = invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null;return this.invokeWithinTransaction(invocation.getMethod(), targetClass, new CoroutinesInvocationCallback() {@Nullablepublic Object proceedWithInvocation() throws Throwable {// 拦截器链式调用return invocation.proceed();}public Object getTarget() {return invocation.getThis();}public Object[] getArguments() {return invocation.getArguments();}});}