Spring5.0源码深度解析之SpringBean声明事务底层实现原理

Spring事务

Spring声明式事务让我们从复杂的事务处理中得到解脱，使我们再也不用去处理这些步骤：获得连接、关闭连接、事务提交和回滚操作。再也不需要在事务相关方法中处理大量的try..catch..finally代码。

Spring中事务的使用虽然已经相对简单的多，但是，还是有很多的使用和配置规则，下面我们开始我们本章重点。

SpringAop基本原理和思想

1、事务保证数据一致性问题，只需要加上@Transactional

2、纯手写SpringAop环绕通知+手动事务就可以声明事务

基于Spring注解方式构建整合JDBC环境

@Repository
public class OrderDao {
    @Autowired()
    private JdbcTemplate jdbcTemplate;
    public void addOrder() {
        jdbcTemplate.update("insert into order_info values(null,'mayikt','zhangsan','1111')");
    }
}

@Configuration
@ComponentScan("com.mayikt")
@EnableTransactionManagement//开启事务注解
public class MyConfig {
    //注入到ioc容器中 beanid =dataSource class=DataSource类的完整路径地址
    // 配置我们的数据源
    @Bean
    public DataSource dataSource() {
        MysqlDataSource mysqlDataSource = new MysqlDataSource();
        mysqlDataSource.setUser("root");
        mysqlDataSource.setPassword("root");
        mysqlDataSource.setURL("jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=UTF-8");
        mysqlDataSource.setDatabaseName("test");
        return mysqlDataSource;
    }
    /**
     * 注入JdbcTemplate
     */
    @Bean
    public JdbcTemplate jdbcTemplate() {
        return new JdbcTemplate(dataSource());
    }
    @Bean
    public PlatformTransactionManager platformTransactionManager(){
         return  new DataSourceTransactionManager(dataSource());
    }
}

@Service
public class OrderServiceImpl implements OrderService {
    @Autowired
    private OrderDao orderDao;
    @Transactional//开启事务
    public void addOrder() {
        try {
            orderDao.addOrder();
            int i = 1 / 0; // 如果报错的情况下肯定是会插入到数据库中
        } catch (Exception e) {
        }
    }
}

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>5.0.5.RELEASE</version>
    </dependency>

    <!-- mysql 依赖 -->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.46</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-jdbc</artifactId>
        <version>5.0.5.RELEASE</version>
    </dependency>
</dependencies>

Spring声明事务底层源码分析

@EnableTransactionManagement//开启事务

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(TransactionManagementConfigurationSelector.class)
public @interface EnableTransactionManagement {

TransactionManagementConfigurationSelector的祖宗是ImportSelector

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[] {TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME};
         default:
            return null;
      }
   }

}

public class AutoProxyRegistrar implements ImportBeanDefinitionRegistrar {//向IOC容器中注入Bean对象
 ....
   @Override
   public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
    ....
         if (mode != null && proxyTargetClass != null && AdviceMode.class == mode.getClass() &&
               Boolean.class == proxyTargetClass.getClass()) {
            candidateFound = true;
            if (mode == AdviceMode.PROXY) {
               AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
               if ((Boolean) proxyTargetClass) {
                  AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
                  return;
               }
            }
         }
      }
     ....
}

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);
}

将InfrastructureAdvisorAutoProxyCreator注入到IOC容器中：

InfrastructureAdvisorAutoProxyCreator的类图如下：祖宗是BeanPostProcessor后置处理器，父类是AbstractAutoProxyCreater

回到registerOrEscalateApcAsRequired方法：beanid为：internalAutoProxyCreator，value为：InfrastructureAdvisorAutoProxyCreator对象

private static BeanDefinition registerOrEscalateApcAsRequired(Class<?> cls, BeanDefinitionRegistry registry, @Nullable Object source) {
    Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
    if (registry.containsBeanDefinition("org.springframework.aop.config.internalAutoProxyCreator")) {
        BeanDefinition apcDefinition = registry.getBeanDefinition("org.springframework.aop.config.internalAutoProxyCreator");
        if (!cls.getName().equals(apcDefinition.getBeanClassName())) {
            int currentPriority = findPriorityForClass(apcDefinition.getBeanClassName());
            int requiredPriority = findPriorityForClass(cls);
            if (currentPriority < requiredPriority) {
                apcDefinition.setBeanClassName(cls.getName());
            }
        }

        return null;
    } else {
        RootBeanDefinition beanDefinition = new RootBeanDefinition(cls);
        beanDefinition.setSource(source);
        beanDefinition.getPropertyValues().add("order", -2147483648);
        beanDefinition.setRole(2);
        registry.registerBeanDefinition("org.springframework.aop.config.internalAutoProxyCreator", beanDefinition);
        return beanDefinition;
    }
}

下面回到ProxyTransactionManagementConfiguration方法

protected String[] selectImports(AdviceMode adviceMode) {
   switch (adviceMode) {
      case PROXY:
         return new String[] {AutoProxyRegistrar.class.getName(), ProxyTransactionManagementConfiguration.class.getName()};
      case ASPECTJ:
         return new String[] {TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME};
      default:
         return null;
   }
}

@Configuration
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;
   }

BeanId:transactionInterceptor;value为：TransactionInterceptor这个对象

打印所有注册的Bean

org.springframework.context.annotation.internalConfigurationAnnotationProcessor
org.springframework.context.annotation.internalAutowiredAnnotationProcessor
org.springframework.context.annotation.internalRequiredAnnotationProcessor
org.springframework.context.annotation.internalCommonAnnotationProcessor
org.springframework.context.event.internalEventListenerProcessor
org.springframework.context.event.internalEventListenerFactory
myConfig
orderDao
orderServiceImpl
org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration
org.springframework.transaction.config.internalTransactionAdvisor
transactionAttributeSource
transactionInterceptor【】【】【】【】这里
org.springframework.transaction.config.internalTransactionalEventListenerFactory
dataSource
jdbcTemplate
platformTransactionManager
org.springframework.aop.config.internalAutoProxyCreator【】【】【】【】这里
 

加上@EnableTransactionManagement这个注解将 ：TransactionInterceptor，和InternalAutoProxyCreator这两个类注入到IOC容器中

下面重点分析这两个类【transactionInterceptor】，【internalAutoProxyCreator】

从上面类结构可知：InfrastructureAdvisorAutoProxyCreator间接实现了SmartInstantiationAwareBeanPostProcessor，而SmartInstantiationAwareBeanPostProcessor又继承自

InstantiationAwareBeanPostProcessor，也就是说在Spring中，所有的bean实例化时Spring都会保证调用其postProcessAfterInstantiation方法，其实现是在父类AbstractAutoProxyCreater中实现的。

我们一旦把这个类：InfrastructureAdvisorAutoProxyCreator注入到容器中，Bean对象在初始化时，会判断是否需要创建代理类。

进入AbstractAutoProxyCreater的后置处理器:

public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) throws BeansException {
    if (bean != null) {
        //根据给定的bean的class和name构建出key，beanClassName_beanName
        Object cacheKey = this.getCacheKey(bean.getClass(), beanName);
        //是否是由于避免循环依赖而创建bean的代理
        if (!this.earlyProxyReferences.contains(cacheKey)) {
            return this.wrapIfNecessary(bean, beanName, cacheKey);
        }
    }
    return bean;
}

这里实现的主要目的是针对指定的bean进行封装，当然首先要确定是否需要封装，检测及封装的工作都委托给了wrapIfNecessary函数进行。

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
    //如果已经处理过
    if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
        return bean;
    } else if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
        return bean;
    } else if (!this.isInfrastructureClass(bean.getClass()) && !this.shouldSkip(bean.getClass(), beanName)) {
        Object[] specificInterceptors = this.getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, (TargetSource)null);
        if (specificInterceptors != DO_NOT_PROXY) {
            this.advisedBeans.put(cacheKey, Boolean.TRUE);
            Object proxy = this.createProxy(bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));//关键点，创建代理，对需要增强的bean创建代理（CGLIBProxy或者JDKProxy）
            this.proxyTypes.put(cacheKey, proxy.getClass());
            return proxy;
        } else {
            this.advisedBeans.put(cacheKey, Boolean.FALSE);
            return bean;
        }
    } else {
        this.advisedBeans.put(cacheKey, Boolean.FALSE);
        return bean;
    }
}

wrapIfNecessary函数功能实现起来很复杂，但是逻辑上还是相对简单，在wrapIfNecessary函数中主要做了以下工作：

1. 找出指定bean对应的增强器【上篇文章详细介绍了，异曲同工】
2. 根据找出的增强器创建代理【上篇文章详细介绍了，异曲同工】

下面简单浏览下：

protected Object[] getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName, @Nullable TargetSource targetSource) {
    List<Advisor> advisors = this.findEligibleAdvisors(beanClass, beanName);
    return advisors.isEmpty() ? DO_NOT_PROXY : advisors.toArray();
}

protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
    List<Advisor> candidateAdvisors = this.findCandidateAdvisors();//寻找候选增强器，这里不介绍了
    List<Advisor> eligibleAdvisors = this.findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);//候选增强器中寻找匹配项，这里分析下
  ....
}

protected List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {
 ....
    try {
        var4 = AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
....
}

public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {
 ....
        while(var3.hasNext()) {
            Advisor candidate = (Advisor)var3.next();
            //首先处理引介增强
            if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
                eligibleAdvisors.add(candidate);
            }
        }
....
        while(var7.hasNext()) {
            Advisor candidate = (Advisor)var7.next();
            //对普通bean的处理
            if (!(candidate instanceof IntroductionAdvisor) && canApply(candidate, clazz, hasIntroductions)) {
                eligibleAdvisors.add(candidate);
            }
....
    }
}

public static boolean canApply(Advisor advisor, Class<?> targetClass, boolean hasIntroductions) {
    if (advisor instanceof IntroductionAdvisor) {
        return ((IntroductionAdvisor)advisor).getClassFilter().matches(targetClass);
    } else if (advisor instanceof PointcutAdvisor) {
        PointcutAdvisor pca = (PointcutAdvisor)advisor;
        return canApply(pca.getPointcut(), targetClass, hasIntroductions);
    } else {
        return true;
    }
}

public static boolean canApply(Pointcut pc, Class<?> targetClass, boolean hasIntroductions) {
    Assert.notNull(pc, "Pointcut must not be null");
    if (!pc.getClassFilter().matches(targetClass)) {
        return false;
    } else {
        MethodMatcher methodMatcher = pc.getMethodMatcher();
      ....
                for(int var11 = 0; var11 < var10; ++var11) {
                    Method method = var9[var11];
                    if (introductionAwareMethodMatcher != null && introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions) || methodMatcher.matches(method, targetClass)) {
                        return true;
....
        }
    }
}

public boolean matches(Method method, @Nullable Class<?> targetClass) {
....
    //自定义标签解析时注入
   TransactionAttributeSource tas = getTransactionAttributeSource();
   return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
}

public TransactionAttribute getTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
....
   else {
      // We need to work it out.
      TransactionAttribute txAttr = computeTransactionAttribute(method, targetClass);
  ....
}

protected TransactionAttribute computeTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
....
   //method代表接口中的方法，specificMethod代表实现类中的方法
   Method specificMethod = AopUtils.getMostSpecificMethod(method, targetClass);

   // First try is the method in the target class.
    //查看方法中是否存在事务声明
   TransactionAttribute txAttr = findTransactionAttribute(specificMethod);
   if (txAttr != null) {
      return txAttr;
   }

   // Second try is the transaction attribute on the target class.
   txAttr = findTransactionAttribute(specificMethod.getDeclaringClass());
   if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {
      return txAttr;
   }
    //如果存在接口，则到接口中去寻找
   if (specificMethod != method) {
      // Fallback is to look at the original method.
      txAttr = findTransactionAttribute(method);
      if (txAttr != null) {
         return txAttr;
      }
      // Last fallback is the class of the original method.
      txAttr = findTransactionAttribute(method.getDeclaringClass());
      if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {
         return txAttr;
      }
   }

   return null;
}

对于事务属性的获取规则相信大家都已经很清楚了，如果方法中存在事务属性，则使用方法上的属性，否则使用方法所在类上的属性，如果方法所在类的属性上还是没有搜寻到对应的事务属性，那么再搜寻接口中的方法，再没有的化，

最好尝试搜寻接口的类上面的声明。对于函数computeTransactionAttribute中的逻辑，就是搭建了一个执行框架而已，将搜寻事务属性任务委托给了findTransactionAttribute方法去执行。下面看看这个方法。

protected TransactionAttribute findTransactionAttribute(Method method) {
   return determineTransactionAttribute(method);
}

protected TransactionAttribute determineTransactionAttribute(AnnotatedElement ae) {
   for (TransactionAnnotationParser annotationParser : this.annotationParsers) {
      TransactionAttribute attr = annotationParser.parseTransactionAnnotation(ae);
      if (attr != null) {
         return attr;
      }
   }
   return null;
}

public TransactionAttribute parseTransactionAnnotation(AnnotatedElement ae) {
   AnnotationAttributes attributes = AnnotatedElementUtils.findMergedAnnotationAttributes(
         ae, Transactional.class, false, false);
   if (attributes != null) {
      return parseTransactionAnnotation(attributes);
   }
   else {
      return null;
   }
}

到这块，我们就看到了我们想看到的获取注解标记的代码。首先会判断当前类是否含有Transactional注解，这是事务属性的基础，当然如果有的化会继续调用parseTransactionAnnotation方法解析详细的属性

protected TransactionAttribute parseTransactionAnnotation(AnnotationAttributes attributes) {
   RuleBasedTransactionAttribute rbta = new RuleBasedTransactionAttribute();
   //解析propagation
   Propagation propagation = attributes.getEnum("propagation");
   rbta.setPropagationBehavior(propagation.value());
    //解析isolation
   Isolation isolation = attributes.getEnum("isolation");
   rbta.setIsolationLevel(isolation.value());
   rbta.setTimeout(attributes.getNumber("timeout").intValue());
   rbta.setReadOnly(attributes.getBoolean("readOnly"));
   rbta.setQualifier(attributes.getString("value"));
   ArrayList<RollbackRuleAttribute> rollBackRules = new ArrayList<>();
   Class<?>[] rbf = attributes.getClassArray("rollbackFor");
   for (Class<?> rbRule : rbf) {
      RollbackRuleAttribute rule = new RollbackRuleAttribute(rbRule);
      rollBackRules.add(rule);
   }
   String[] rbfc = attributes.getStringArray("rollbackForClassName");
   for (String rbRule : rbfc) {
      RollbackRuleAttribute rule = new RollbackRuleAttribute(rbRule);
      rollBackRules.add(rule);
   }
   Class<?>[] nrbf = attributes.getClassArray("noRollbackFor");
   for (Class<?> rbRule : nrbf) {
      NoRollbackRuleAttribute rule = new NoRollbackRuleAttribute(rbRule);
      rollBackRules.add(rule);
   }
   String[] nrbfc = attributes.getStringArray("noRollbackForClassName");
   for (String rbRule : nrbfc) {
      NoRollbackRuleAttribute rule = new NoRollbackRuleAttribute(rbRule);
      rollBackRules.add(rule);
   }
   rbta.getRollbackRules().addAll(rollBackRules);
   return rbta;
}

上面方法实现了对对应类或者方法的事务属性解析，你会看到这个类中你所属性的属性。至此，事务功能的初始化工作便结束了

事务增强器

springaop在事务进行调用的时候会走transactionInterceptor进行拦截

执行目标方法，进入invoke()

Spring声明事务源码分析

1.@EnableTransactionManagement开启到我们的事务

2.@Import(TransactionManagementConfigurationSelector.class)

3. AdviceMode mode() default AdviceMode.PROXY;默认使用 PROXY选择器

4.return new String[] {AutoProxyRegistrar.class.getName(), ProxyTransactionManagementConfiguration.class.getName()};

5.加上@EnableTransactionManagement这个注解将 ：TransactionInterceptor，和InternalAutoProxyCreator这两个类注入到IOC容器中

6.进入AbstractAutoProxyCreater的后置处理器的wrapIfNecessary方法针对指定bean进行封装

####6.1.找出指定bean对应的增强器

####6.2.根据找出的增强器创建代理

7.执行目标方法

8.一旦出现异常，尝试异常处理，默认 对（RuntimeException回滚）

9.提交事务前的事务信息清除

10.提交事务。

本文参考

参考书籍：Spring源码深度解析

蚂蚁课堂：http://www.mayikt.com/