Spring事務

Spring聲明式事務讓我們從複雜的事務處理中得到解脫，使我們再也不用去處理這些步驟：獲得連接、關閉連接、事務提交和回滾操作。再也不需要在事務相關方法中處理大量的try..catch..finally代碼。

Spring中事務的使用雖然已經相對簡單的多，但是，還是有很多的使用和配置規則，下面我們開始我們本章重點。

SpringAop基本原理和思想

1、事務保證數據一致性問題，只需要加上@Transactional

2、純手寫SpringAop環繞通知+手動事務就可以聲明事務

基於Spring註解方式構建整合JDBC環境

@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//開啓事務註解
public class MyConfig {
    //注入到ioc容器中 beanid =dataSource class=DataSource類的完整路徑地址
    // 配置我們的數據源
    @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//開啓事務
    public void addOrder() {
        try {
            orderDao.addOrder();
            int i = 1 / 0; // 如果報錯的情況下肯定是會插入到數據庫中
        } catch (Exception e) {
        }
    }
}

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

    <!-- mysql 依賴 -->
    <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聲明事務底層源碼分析

@EnableTransactionManagement//開啓事務

@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對象
 ....
   @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);
}

將InfrastructureAdvisorAutoProxyCreator注入到IOC容器中：

InfrastructureAdvisorAutoProxyCreator的類圖如下：祖宗是BeanPostProcessor後置處理器，父類是AbstractAutoProxyCreater

回到registerOrEscalateApcAsRequired方法：beanid爲：internalAutoProxyCreator，value爲：InfrastructureAdvisorAutoProxyCreator對象

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爲：TransactionInterceptor這個對象

打印所有註冊的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【】【】【】【】這裏
org.springframework.transaction.config.internalTransactionalEventListenerFactory
dataSource
jdbcTemplate
platformTransactionManager
org.springframework.aop.config.internalAutoProxyCreator【】【】【】【】這裏

加上@EnableTransactionManagement這個註解將：TransactionInterceptor，和InternalAutoProxyCreator這兩個類注入到IOC容器中

下面重點分析這兩個類【transactionInterceptor】，【internalAutoProxyCreator】

從上面類結構可知：InfrastructureAdvisorAutoProxyCreator間接實現了SmartInstantiationAwareBeanPostProcessor，而SmartInstantiationAwareBeanPostProcessor又繼承自

InstantiationAwareBeanPostProcessor，也就是說在Spring中，所有的bean實例化時Spring都會保證調用其postProcessAfterInstantiation方法，其實現是在父類AbstractAutoProxyCreater中實現的。

我們一旦把這個類：InfrastructureAdvisorAutoProxyCreator注入到容器中，Bean對象在初始化時，會判斷是否需要創建代理類。

進入AbstractAutoProxyCreater的後置處理器:

public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) throws BeansException {
    if (bean != null) {
        //根據給定的bean的class和name構建出key，beanClassName_beanName
        Object cacheKey = this.getCacheKey(bean.getClass(), beanName);
        //是否是由於避免循環依賴而創建bean的代理
        if (!this.earlyProxyReferences.contains(cacheKey)) {
            return this.wrapIfNecessary(bean, beanName, cacheKey);
        }
    }
    return bean;
}

這裏實現的主要目的是針對指定的bean進行封裝，當然首先要確定是否需要封裝，檢測及封裝的工作都委託給了wrapIfNecessary函數進行。

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
    //如果已經處理過
    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));//關鍵點，創建代理，對需要增強的bean創建代理（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函數功能實現起來很複雜，但是邏輯上還是相對簡單，在wrapIfNecessary函數中主要做了以下工作：

找出指定bean對應的增強器【上篇文章詳細介紹了，異曲同工】

根據找出的增強器創建代理【上篇文章詳細介紹了，異曲同工】

下面簡單瀏覽下：

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();//尋找候選增強器，這裏不介紹了
    List<Advisor> eligibleAdvisors = this.findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);//候選增強器中尋找匹配項，這裏分析下
  ....
}

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();
            //首先處理引介增強
            if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
                eligibleAdvisors.add(candidate);
            }
        }
....
        while(var7.hasNext()) {
            Advisor candidate = (Advisor)var7.next();
            //對普通bean的處理
            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) {
....
    //自定義標籤解析時注入
   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代表實現類中的方法
   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務聲明
   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，則到接口中去尋找
   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;
}

對於事務屬性的獲取規則相信大家都已經很清楚了，如果方法中存在事務屬性，則使用方法上的屬性，否則使用方法所在類上的屬性，如果方法所在類的屬性上還是沒有搜尋到對應的事務屬性，那麼再搜尋接口中的方法，再沒有的化，

最好嘗試搜尋接口的類上面的聲明。對於函數computeTransactionAttribute中的邏輯，就是搭建了一個執行框架而已，將搜尋事務屬性任務委託給了findTransactionAttribute方法去執行。下面看看這個方法。

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;
   }
}

到這塊，我們就看到了我們想看到的獲取註解標記的代碼。首先會判斷當前類是否含有Transactional註解，這是事務屬性的基礎，當然如果有的化會繼續調用parseTransactionAnnotation方法解析詳細的屬性

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;
}

上面方法實現了對對應類或者方法的事務屬性解析，你會看到這個類中你所屬性的屬性。至此，事務功能的初始化工作便結束了

事務增強器

springaop在事務進行調用的時候會走transactionInterceptor進行攔截

執行目標方法，進入invoke()

Spring聲明事務源碼分析

1.@EnableTransactionManagement開啓到我們的事務

2.@Import(TransactionManagementConfigurationSelector.class)

3. AdviceMode mode() default AdviceMode.PROXY;默認使用 PROXY選擇器

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

5.加上@EnableTransactionManagement這個註解將：TransactionInterceptor，和InternalAutoProxyCreator這兩個類注入到IOC容器中

6.進入AbstractAutoProxyCreater的後置處理器的wrapIfNecessary方法針對指定bean進行封裝

####6.1.找出指定bean對應的增強器

####6.2.根據找出的增強器創建代理

7.執行目標方法

8.一旦出現異常，嘗試異常處理，默認對（RuntimeException回滾）

9.提交事務前的事務信息清除

10.提交事務。

本文參考

參考書籍：Spring源碼深度解析

螞蟻課堂：http://www.mayikt.com/

Spring5.0源碼深度解析之SpringBean聲明事務底層實現原理

Spring事務

SpringAop基本原理和思想

基於Spring註解方式構建整合JDBC環境

Spring聲明事務底層源碼分析

事務增強器

Spring聲明事務源碼分析

本文參考

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