spring声明事务和注解事务(一文详解Spring事务注解的解析)
spring声明事务和注解事务(一文详解Spring事务注解的解析)private static final List<Class<?>> APC_PRIORITY_LIST = new ArrayList<>(3); static { // Set up the escalation list... APC_PRIORITY_LIST.add(InfrastructureAdvisorAutoProxyCreator.class); APC_PRIORITY_LIST.add(AspectJAwareAdvisorAutoProxyCreator.class); APC_PRIORITY_LIST.add(AnnotationAwareAspectJAutoProxyCreator.class); } private static int findPriorityForClass(@Nulla
前言事务我们都知道是什么,而Spring事务就是在数据库之上利用Aop提供声明式事务和编程式事务帮助我们简化开发,解耦业务逻辑和系统逻辑。但是Spring事务原理是怎样?事务在方法间是如何传播的?为什么有时候事务会失效?接下来几篇文章将重点分析Spring事务源码,让我们彻底搞懂Spring事务的原理。
XML标签的解析<tx:annotation-driven transaction-manager="transactionManager"/>
配置过事务的应该都不陌生,上面这个配置就是Spring开启事务注解(@Transactional)支持的配置,而看过我之前文章的应该知道,这个带前缀的标签叫自定义标签,我在之前的文章也分析过自定义标签的解析过程,所以这里我直接找到对应的handler:
public class TxNamespaceHandler extends NamespaceHandlerSupport {
static final String TRANSACTION_MANAGER_ATTRIBUTE = "transaction-manager";
static final String DEFAULT_TRANSACTION_MANAGER_BEAN_NAME = "transactionManager";
static String getTransactionManagerName(Element element) {
return (element.hasAttribute(TRANSACTION_MANAGER_ATTRIBUTE) ?
element.getAttribute(TRANSACTION_MANAGER_ATTRIBUTE) : DEFAULT_TRANSACTION_MANAGER_BEAN_NAME);
}
@Override
public void init() {
registerBeanDefinitionParser("advice" new TxAdviceBeanDefinitionParser());
registerBeanDefinitionParser("annotation-driven" new AnnotationDrivenBeanDefinitionParser());
registerBeanDefinitionParser("Jta-transaction-manager" new JtaTransactionManagerBeanDefinitionParser());
}
}
可以看到对应的注解解析器就是AnnotationDrivenBeanDefinitionParser类,在该类中一定会有一个parse方法:
public BeanDefinition parse(Element element ParserContext parserContext) {
registerTransactionalEventListenerFactory(parserContext);
String mode = element.getAttribute("mode");
if ("aspectj".equals(mode)) {
// mode="aspectj"
registerTransactionAspect(element parserContext);
if (ClassUtils.isPresent("javax.transaction.Transactional" getClass().getClassLoader())) {
registerJtaTransactionAspect(element parserContext);
}
}
else {
// mode="proxy"
AOPAutoProxyConfigurer.configureAutoProxyCreator(element parserContext);
}
return null;
}
首先拿到mode属性的值判断是使用AspectJ生成代理还是JDK生成代理,这里我们主要看proxy模式,进入configureAutoProxyCreator方法:
public static void configureAutoProxyCreator(Element element ParserContext parserContext) {
// 注册AOP的入口类
AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext element);
String txAdvisorBeanName = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME;
if (!parserContext.getRegistry().containsBeanDefinition(txAdvisorBeanName)) {
Object eleSource = parserContext.extractSource(element);
// Create the TransactionAttributeSource definition.
// @Transactional注解的属性封装
RootBeanDefinition sourceDef = new RootBeanDefinition(
"org.springframework.transaction.annotation.AnnotationTransactionAttributeSource");
sourceDef.setSource(eleSource);
sourceDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
String sourceName = parserContext.getReaderContext().registerWithGeneratedName(sourceDef);
// Create the TransactionInterceptor definition.
// AOP执行链
RootBeanDefinition interceptorDef = new RootBeanDefinition(TransactionInterceptor.class);
interceptorDef.setSource(eleSource);
interceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
// 拿到transaction-manager属性的值
registerTransactionManager(element interceptorDef);
interceptorDef.getPropertyValues().add("transactionAttributeSource" new RuntimeBeanReference(sourceName));
String interceptorName = parserContext.getReaderContext().registerWithGeneratedName(interceptorDef);
// Create the TransactionAttributeSourceAdvisor definition.
RootBeanDefinition advisorDef = new RootBeanDefinition(BeanFactoryTransactionAttributeSourceAdvisor.class);
advisorDef.setSource(eleSource);
advisorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
advisorDef.getPropertyValues().add("transactionAttributeSource" new RuntimeBeanReference(sourceName));
advisorDef.getPropertyValues().add("adviceBeanName" interceptorName);
if (element.hasAttribute("order")) {
advisorDef.getPropertyValues().add("order" element.getAttribute("order"));
}
parserContext.getRegistry().registerBeanDefinition(txAdvisorBeanName advisorDef);
CompositeComponentDefinition compositeDef = new CompositeComponentDefinition(element.getTagName() eleSource);
compositeDef.addNestedComponent(new BeanComponentDefinition(sourceDef sourceName));
compositeDef.addNestedComponent(new BeanComponentDefinition(interceptorDef interceptorName));
compositeDef.addNestedComponent(new BeanComponentDefinition(advisorDef txAdvisorBeanName));
parserContext.registerComponent(compositeDef);
}
}
这里的流程比较长,但逻辑很简单。首先来看注册事务AOP入口类是哪个:
public static void registerAutoProxyCreatorIfNecessary(
ParserContext parserContext Element sourceElement) {
// 将优先级更高的AOP入口类放入到IOC容器中
BeanDefinition beanDefinition = AopConfigUtils.registerAutoProxyCreatorIfNecessary(
parserContext.getRegistry() parserContext.extractSource(sourceElement));
// 设置代理生成的方式以及是否缓存代理类到当前线程
useClassProxyingIfNecessary(parserContext.getRegistry() sourceElement);
registerComponentIfNecessary(BeanDefinition parserContext);
}
主要看registerAutoProxyCreatorIfNecessary方法:
public static BeanDefinition registerAutoProxyCreatorIfNecessary(
BeanDefinitionRegistry registry @Nullable Object source) {
return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class registry source);
}
private static BeanDefinition registerOrEscalateApcAsRequired(
Class<?> cls BeanDefinitionRegistry registry @Nullable Object source) {
Assert.notNull(registry "BeanDefinitionRegistry must not be null");
// 判断传进来的类和ICO中当前存在的类哪个优先级更高,将更高的放入IOC中
if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {
BeanDefinition apcDefinition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);
if (!cls.getName().equals(apcDefinition.getBeanClassName())) {
int currentPriority = findPriorityForClass(apcDefinition.getBeanClassName());
int requiredPriority = findPriorityForClass(cls);
if (currentPriority < requiredPriority) {
apcDefinition.setBeanClassName(cls.getName());
}
}
return null;
}
//把AOP入口类封装成beanDefinition对象,要实例化
RootBeanDefinition beanDefinition = new RootBeanDefinition(cls);
beanDefinition.setSource(source);
beanDefinition.getPropertyValues().add("order" Ordered.HIGHEST_PRECEDENCE);
beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
//注解aop入口类的beanName名称 AopConfigUtils.AUTO_PROXY_CREATOR_BEAN_NAME
registry.registerBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME beanDefinition);
return beanDefinition;
}
首先判断容器中是否已经存在AOP入口类,如果不存在则直接创建InfrastructureAdvisorAutoProxyCreator的BeanDefinition对象注册到容器中,这个类也是AOP入口类AbstractAutoProxyCreator的子类,再来看看其继承关系:
你会不会疑惑,这么多子类,到底会使用哪一个呢?回到刚刚的代码中,可以看到如果已经存在一个入口类了,就会通过findPriorityForClass获取两个类的优先级,最终就会使用优先级更大的那个,那么它们的优先级顺序是怎样的呢?
private static final List<Class<?>> APC_PRIORITY_LIST = new ArrayList<>(3);
static {
// Set up the escalation list...
APC_PRIORITY_LIST.add(InfrastructureAdvisorAutoProxyCreator.class);
APC_PRIORITY_LIST.add(AspectJAwareAdvisorAutoProxyCreator.class);
APC_PRIORITY_LIST.add(AnnotationAwareAspectJAutoProxyCreator.class);
}
private static int findPriorityForClass(@Nullable String className) {
// 索引即是优先级,越大优先级越高,IOC中只会存在一个事务AOP入口类
for (int i = 0; i < APC_PRIORITY_LIST.size(); i ) {
Class<?> clazz = APC_PRIORITY_LIST.get(i);
if (clazz.getName().equals(className)) {
return i;
}
}
throw new IllegalArgumentException(
"Class name [" className "] is not a known auto-proxy creator class");
}
可以看到,InfrastructureAdvisorAutoProxyCreator是优先级最低的,基本上不会起作用;AspectJAwareAdvisorAutoProxyCreator是当我们配置了<aop:config>标签时会注册,也就是xml配置的AOP的入口类;而AnnotationAwareAspectJAutoProxyCreator是当我们配置了<aop:aspectj-autoproxy>或使用@EnableAspectJAutoProxy注解时注册,因此大部分情况下都是使用的AnnotationAwareAspectJAutoProxyCreator。
注册完AOP的入口类后,回到configureAutoProxyCreator方法:
RootBeanDefinition sourceDef = new RootBeanDefinition(
"org.springframework.transaction.annotation.AnnotationTransactionAttributeSource");
sourceDef.setSource(eleSource);
sourceDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
String sourceName =parserContext.getReaderContext().registerWithGeneratedName(sourceDef);
AnnotationTransactionAttributeSource类的作用就是封装事务注解@Transactional的属性,这里需要记住其继承体系以及熟悉该类和其父类的属性和方法,对后面分析事物切面执行原理有帮助:
紧接着就是创建了TransactionInterceptor对象,专门的事务拦截器,并且该类是MethodInterceptor的子类,看到这个应该不陌生了,我们知道AOP调用链在执行过程中主要就是调用该类的invoke的方法,因此它是事务切面执行的入口。既然有了Interceptor,那么必不可少的还应该有Advisor,而Advisor又是由Advice和Poincut组成的,这样才能构成一个完整的切面,所以该方法后面就是创建这两个对象。以上就是xml配置AOP注解支持的原理,很简单,下面再来看看零配置又是如何实现的。
AOP零配置原理使用过SpringBoot的都知道,如果需要开启事务注解的支持,只需要一个注解就能搞定:@EnableTransactionManagement,不用再配置xml文件,这个又是怎么做到的呢?不多说,我们直接来看其源码:
@Import(TransactionManagementConfigurationSelector.class)
public @interface EnableTransactionManagement {
boolean proxyTargetClass() default false;
AdviceMode mode() default AdviceMode.PROXY;
int order() default Ordered.LOWEST_PRECEDENCE;
}
在该注解下使用@Import导入了一个类TransactionManagementConfigurationSelector,首先该注解的作用就是导入一个类的实例到IOC容器中,你可能会说不是在类上加@Component注解就行了么,但是有些类它并不在你扫描的路径下,而该注解依然可以将其导入进来,所以我么主要看TransactionManagementConfigurationSelector类中做了些啥:
public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> {
@Override
protected String[] selectImports(AdviceMode adviceMode) {
switch (adviceMode) {
case PROXY:
return new String[] {AutoProxyRegistrar.class.getName()
ProxyTransactionManagementConfiguration.class.getName()};
case ASPECTJ:
return new String[] {determineTransactionAspectClass()};
default:
return null;
}
}
private String determineTransactionAspectClass() {
return (ClassUtils.isPresent("javax.transaction.Transactional" getClass().getClassLoader()) ?
TransactionManagementConfigUtils.JTA_TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME :
TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME);
}
}
可以看到在selectImports方法中返回了AutoProxyRegistrar和ProxyTransactionManagementConfiguration类,返回后会被封装为BeanDefinition对象,那这个方法是在哪里调用的呢?这个在之前的文章中也分析过,ConfigurationClassPostProcessor类中会调用ConfigurationClassParser类的parse方法解析@Configuration、@Import、@ImportSource等注解,具体过程这里就不再赘述了。我们继续来分别看看AutoProxyRegistrar和ProxyTransactionManagementConfiguration类:
public class AutoProxyRegistrar implements ImportBeanDefinitionRegistrar {
private final Log logger = LogFactory.getLog(getClass());
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata BeanDefinitionRegistry registry) {
boolean candidateFound = false;
Set<String> annoTypes = importingClassMetadata.getAnnotationTypes();
for (String annoType : annoTypes) {
AnnotationAttributes candidate = AnnotationConfigUtils.attributesFor(importingClassMetadata annoType);
if (candidate == null) {
continue;
}
Object mode = candidate.get("mode");
Object proxyTargetClass = candidate.get("proxyTargetClass");
if (mode != null && proxyTargetClass != null && AdviceMode.class == mode.getClass() &&
Boolean.class == proxyTargetClass.getClass()) {
candidateFound = true;
if (mode == AdviceMode.PROXY) {
//注册事务AOP的入口类InfrastructureAdvisorAutoProxyCreator 实际上这个AOP入口类起不了作用
AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
if ((Boolean) proxyTargetClass) {
AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
return;
}
}
}
}
}
}
public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration {
/*
* 明显是创建事务切面实例
* BeanFactoryTransactionAttributeSourceAdvisor
*
* */
@Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor() {
BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();
advisor.setTransactionAttributeSource(transactionAttributeSource());
//设置通知类
advisor.setAdvice(transactionInterceptor());
if (this.enableTx != null) {
advisor.setOrder(this.enableTx.<Integer>getNumber("order"));
}
return advisor;
}
@Bean
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public TransactionAttributeSource transactionAttributeSource() {
return new AnnotationTransactionAttributeSource();
}
/*
* 创建事务advice
* TransactionInterceptor
* */
@Bean
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public TransactionInterceptor transactionInterceptor() {
TransactionInterceptor interceptor = new TransactionInterceptor();
interceptor.setTransactionAttributeSource(transactionAttributeSource());
//事务管理器要跟数据源挂钩,所以需要自己定义
if (this.txManager != null) {
interceptor.setTransactionManager(this.txManager);
}
return interceptor;
}
}
看到这就很清楚了,前者是注册AOP的入口类(这里注册的入口类依然是InfrastructureAdvisorAutoProxyCreator),后者则是创建事务AOP的组件的实例到IOC中,到这里相信不仅仅是对于事务的零配置,而是整个SpringBoot的零配置实现原理都心中有数了。
作者:夜勿语
原文链接:https://blog.csdn.net/l6108003/article/details/106650023