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

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发布于 2019-09-02 16:02:34

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发布于 2019-09-02 16:02:34

测试Demo

本篇文章的Demo基于上一篇文章SpringJDBC源码解析新添加内容如下首先在配置类中添加开启事务的注解@EnableTransactionManagement 然后添加DataSourceTransactionManagerBean

@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 https://github.com/shiyujun/spring-framework

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注解源码解析这里就不再详细解释了，直接看类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，走的是第一个分枝所以在这里往Spring容器中注入了两个beanAutoProxyRegistrar、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

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