Spring事务源码解析（一）@EnableTransactionManagement注解

客官°小女子只卖身不卖艺 2024-04-18 20:39 80阅读 0赞

#### **测试Demo** ####

本篇文章的Demo基于上一篇文章[SpringJDBC源码解析][SpringJDBC]`@EnableTransactionManagement``DataSourceTransactionManager`Bean

@Beanpublic DataSourceTransactionManager 	
    dataSourceTransactionManager(DruidDataSource druidDataSource) {    	
            return new DataSourceTransactionManager(druidDataSource);	
            }

在业务接口中新增一个抛出异常的修改方法

public interface JDBCService {	
        public void testTransactional();	
    } 	
    @Transactional	
    public class JDBCServiceImpl implements JDBCService {	
    
    	
        @Override	
        public void testTransactional() {	
            jdbcTemplate.update("update user set name='王五' where id=1", new Object[]{});	
            throw new RuntimeException("异常");	
        }	
    }

启动Demo的类

public class TransactionalDemo {	
        public static void main (String args[]){	
            ApplicationContext context = new AnnotationConfigApplicationContext("cn.shiyujun.config");	
            JDBCService jdbcService=  context.getBean(JDBCService.class);	
            jdbcService.testTransactional();	
        }	
    }

至此Deno工程搭建完毕，有需要源码的同学可以从下方地址获取

#####     #####

##### **源码解析** #####

可以看到我们的事务是通过`EnableTransactionManagement`注解启用的，所以此次源码解析也从此注解开始

@Target({ElementType.TYPE})	
    @Retention(RetentionPolicy.RUNTIME)	
    @Documented	
    @Import({TransactionManagementConfigurationSelector.class})	
    public @interface EnableTransactionManagement {	
        boolean proxyTargetClass() default false;	
    
    	
        AdviceMode mode() default AdviceMode.PROXY;	
    
    	
        int order() default 2147483647;	
    }

相信看过我之前文章的同学都已经知道了`@Import`注解的原理了[Spring @Import注解源码解析][Spring _Import]`TransactionManagementConfigurationSelector`吧

public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> {	
        public TransactionManagementConfigurationSelector() {	
        }	
    
    	
        protected String[] selectImports(AdviceMode adviceMode) {	
            switch(adviceMode) {	
            case PROXY:	
                return new String[]{AutoProxyRegistrar.class.getName(), ProxyTransactionManagementConfiguration.class.getName()};	
            case ASPECTJ:	
                return new String[]{"org.springframework.transaction.aspectj.AspectJTransactionManagementConfiguration"};	
            default:	
                return null;	
            }	
        }	
    }

可以看到这里是根据`@EnableTransactionManagement`注解的`mode`属性来确认注入哪一个配置类。这里由于我们没有指定属性，所以使用的默认的PROXY代理，走的是第一个分枝`AutoProxyRegistrar`、`ProxyTransactionManagementConfiguration`

##### **创建自动代理的构建器** #####

`AutoProxyRegistrar`类里面核心方法只有这一个

public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {	
      boolean candidateFound = false;	
      Set<String> annoTypes = importingClassMetadata.getAnnotationTypes();	
      for (String annoType : annoTypes) {	
        //获取注解元信息	
        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) {	
              //由于咱们使用的默认PROXY所以走这个分支	
            AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);	
                      //强制使用Cglib动态代理	
            if ((Boolean) proxyTargetClass) {	
              AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);	
              return;	
            }	
          }	
        }	
      }	
      if (!candidateFound) {	
        String name = getClass().getSimpleName();	
        logger.warn(String.format("%s was imported but no annotations were found " +	
            "having both 'mode' and 'proxyTargetClass' attributes of type " +	
            "AdviceMode and boolean respectively. This means that auto proxy " +	
            "creator registration and configuration may not have occurred as " +	
            "intended, and components may not be proxied as expected. Check to " +	
            "ensure that %s has been @Import'ed on the same class where these " +	
            "annotations are declared; otherwise remove the import of %s " +	
            "altogether.", name, name, name));	
      }	
    }

往下看

public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry) {	
           return registerAutoProxyCreatorIfNecessary(registry, (Object)null);	
       }	
      public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, @Nullable Object source) {	
           return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);	
       }	
       private static BeanDefinition registerOrEscalateApcAsRequired(Class<?> cls, BeanDefinitionRegistry registry, Object source) {	
           Assert.notNull(registry, "BeanDefinitionRegistry must not be null");	
           // 定义有AUTO_PROXY_CREATOR_BEAN_NAME="org.springframework.aop.config.internalAutoProxyCreator"	
           if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {	
               // 如果容器中已经存在自动代理构建器，则比较两个构建器的优先级	
               BeanDefinition apcDefinition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);	
               if (!cls.getName().equals(apcDefinition.getBeanClassName())) {	
                   int currentPriority = findPriorityForClass(apcDefinition.getBeanClassName());	
                   int requiredPriority = findPriorityForClass(cls);	
                   // 保存优先级高的构建器	
                   if (currentPriority < requiredPriority) {	
                       apcDefinition.setBeanClassName(cls.getName());	
                   }	
               }	
               return null;	
           }	
           // 如果容器中还没有自动代理构建器	
           // 则创建构建器相应的BeanDefinition对象 	
           RootBeanDefinition beanDefinition = new RootBeanDefinition(cls);	
           beanDefinition.setSource(source);	
           beanDefinition.getPropertyValues().add("order", Ordered.HIGHEST_PRECEDENCE);	
           beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);	
    
    	
           // 向容器中注册代理构建器的BeanDefinition对象	
           registry.registerBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME, beanDefinition);	
           return beanDefinition;	
       }

也就是说这一块的流程主要是为了注册`org.springframework.aop.config.internalAutoProxyCreator`这个bean

##### **事务核心bean的构建** #####

public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration {	
    
    	
      @Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)	
      @Role(BeanDefinition.ROLE_INFRASTRUCTURE)	
      public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor() {	
        BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();	
        advisor.setTransactionAttributeSource(transactionAttributeSource());	
        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();	
      }	
    
    	
      @Bean	
      @Role(BeanDefinition.ROLE_INFRASTRUCTURE)	
      public TransactionInterceptor transactionInterceptor() {	
        TransactionInterceptor interceptor = new TransactionInterceptor();	
        interceptor.setTransactionAttributeSource(transactionAttributeSource());	
        if (this.txManager != null) {	
          interceptor.setTransactionManager(this.txManager);	
        }	
        return interceptor;	
      }	
    
    	
    }

进入这个类之后可以看到这个类是一个配置类，这个类一共注册了三个bean，不要小瞧这三个bean，就是它们三个完成了整个Spring的事务功能

再仔细看的话会发现，`AnnotationTransactionAttributeSource`和`TransactionInterceptor`这两个bea又都注册到了`BeanFactoryTransactionAttributeSourceAdvisor`中，可以看出来这里是一个重点了

> 限于平台字数限制，本篇文章就到这里

![640?wx\_fmt=gif][640_wx_fmt_gif]

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