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Spring事务处理原理步骤详解

运维开发网 https://www.qedev.com 2020-12-23 04:46 出处:网络 作者: 天际星痕
1、事务处理实现 实现步骤: * 声明式事务: * * 环境搭建: * 1、导入相关依赖 * 数据源、数据库驱动、Spring-jdbc模块

1、事务处理实现

实现步骤:

* 声明式事务:

*

* 环境搭建:

* 1、导入相关依赖

* 数据源、数据库驱动、Spring-jdbc模块

* 2、配置数据源、JdbcTemplate(Spring提供的简化数据库操作的工具)操作数据

* 3、给方法上标注 @Transactional 表示当前方法是一个事务方法;

* 4、 @EnableTransactionManagement 开启基于注解的事务管理功能;

* @EnableXXX

* 5、配置事务管理器来控制事务;

* @Bean

* public PlatformTransactionManager transactionManager()

代码实现:

@EnableTransactionManagement
@ComponentScan("com.atguigu.tx")
@Configuration
public class TxConfig {
   
  //数据源
  @Bean
  public DataSource dataSource() throws Exception{
    ComboPooledDataSource dataSource = new ComboPooledDataSource();
    dataSource.setUser("root");
    dataSource.setPassword("123456");
    dataSource.setDriverClass("com.mysql.jdbc.Driver");
    dataSource.setJdbcUrl("jdbc:mysql://localhost:3306/test");
    return dataSource;
  }
   
  @Bean
  public JdbcTemplate jdbcTemplate() throws Exception{
    [email protected];给容器中加组件的方法,多次调用都只是从容器中找组件
    JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource());
    return jdbcTemplate;
  }
   
  //注册事务管理器在容器中
  @Bean
  public PlatformTransactionManager transactionManager() throws Exception{
    return new DataSourceTransactionManager(dataSource());
  }
} 

2、事务处理原理

原理分析:

* 原理:

* 1)[email protected]

* 利用TransactionManagementConfigurationSelector给容器中会导入组件

* 导入两个组件

* AutoProxyRegistrar

* ProxyTransactionManagementConfiguration

* 2)、AutoProxyRegistrar:

* 给容器中注册一个 InfrastructureAdvisorAutoProxyCreator 组件;

* InfrastructureAdvisorAutoProxyCreator:?

* 利用后置处理器机制在对象创建以后,包装对象,返回一个代理对象(增强器),代理对象执行方法利用拦截器链进行调用;

*

* 3)、ProxyTransactionManagementConfiguration 做了什么?

* 1、给容器中注册事务增强器;

* 1)、事务增强器要用事务注解的信息,AnnotationTransactionAttributeSource解析事务注解

* 2)、事务拦截器:

* TransactionInterceptor;保存了事务属性信息,事务管理器;

* 他是一个 MethodInterceptor;

* 在目标方法执行的时候;

* 执行拦截器链;

* 事务拦截器:

* 1)、先获取事务相关的属性

* 2)、再获取PlatformTransactionManager,如果事先没有添加指定任何transactionmanger

* 最终会从容器中按照类型获取一个PlatformTransactionManager;

* 3)、执行目标方法

* 如果异常,获取到事务管理器,利用事务管理回滚操作;

* 如果正常,利用事务管理器,提交事务

*

*/

核心代码

1、EnableTransactionManagement注解,注入TransactionManagementConfigurationSelector类

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

2、TransactionManagementConfigurationSelector类,最终会导入AutoProxyRegistrar.class和ProxyTransactionManagementConfiguration.class两个组件。

public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> {
 
  /**
   * Returns [email protected] ProxyTransactionManagementConfiguration} or
   * [email protected] AspectJ(Jta)TransactionManagementConfiguration} for [email protected] PROXY}
   * and [email protected] ASPECTJ} values of [email protected] EnableTransactionManagement#mode()},
   * respectively.
   */
  @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);
  }
 
}

3、AutoProxyRegistrar类的作用为:

  给容器中注册一个 InfrastructureAdvisorAutoProxyCreator 组件;

  最终的目的是:利用后置处理器机制在对象创建以后,包装对象,返回一个代理对象(增强器),代理对象执行方法利用拦截器链进行调用;

@Override
  public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
    boolean candidateFound = false;
    Set<String> annTypes = importingClassMetadata.getAnnotationTypes();
    for (String annType : annTypes) {
      AnnotationAttributes candidate = AnnotationConfigUtils.attributesFor(importingClassMetadata, annType);
      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) {
          AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
          if ((Boolean) proxyTargetClass) {
            AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
            return;
          }
        }
      }
    }
    if (!candidateFound && logger.isInfoEnabled()) {
      String name = getClass().getSimpleName();
      logger.info(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));
    }
  }

Spring事务处理原理步骤详解

InfrastructureAdvisorAutoProxyCreator类的作用与AnnotationAwareAspectJAutoProxyCreator类的作用类似。

@SuppressWarnings("serial")
public abstract class AbstractAutoProxyCreator extends ProxyProcessorSupport
    implements SmartInstantiationAwareBeanPostProcessor, BeanFactoryAware {

4、ProxyTransactionManagementConfiguration类

代理事务管理配置类

@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;
  }
 
  @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;
  }
 
}

TransactionInterceptor类,事务调用:invokeWithinTransaction()方法为最终执行的方法

@Override
  @Nullable
  public Object invoke(MethodInvocation invocation) throws Throwable {
    // Work out the target class: may be [email protected] null}.
    // The TransactionAttributeSource should be passed the target class
    // as well as the method, which may be from an interface.
    Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);
 
    // Adapt to TransactionAspectSupport's invokeWithinTransaction...
    return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);
  }

TransactionAspectSupport类的最终事务方法执行:

@Nullable
  protected Object invokeWithinTransaction(Method method, @Nullable Class<?> targetClass,
      final InvocationCallback invocation) throws Throwable {
 
    // If the transaction attribute is null, the method is non-transactional.
    TransactionAttributeSource tas = getTransactionAttributeSource();
    final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
    final PlatformTransactionManager tm = determineTransactionManager(txAttr);
    final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
 
    if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
      // Standard transaction demarcation with getTransaction and commit/rollback calls.
      TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
 
      Object retVal;
      try {
        // This is an around advice: Invoke the next interceptor in the chain.
        // This will normally result in a target object being invoked.
        retVal = invocation.proceedWithInvocation();
      }
      catch (Throwable ex) {
        // target invocation exception
        completeTransactionAfterThrowing(txInfo, ex);
        throw ex;
      }
      finally {
        cleanupTransactionInfo(txInfo);
      }
      commitTransactionAfterReturning(txInfo);
      return retVal;
    }
 
    else {
      final ThrowableHolder throwableHolder = new ThrowableHolder();
 
      // It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
      try {
        Object result = ((CallbackPreferringPlatformTransactionManager) tm).execute(txAttr, status -> {
          TransactionInfo txInfo = prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);
          try {
            return invocation.proceedWithInvocation();
          }
          catch (Throwable ex) {
            if (txAttr.rollbackOn(ex)) {
              // A RuntimeException: will lead to a rollback.
              if (ex instanceof RuntimeException) {
                throw (RuntimeException) ex;
              }
              else {
                throw new ThrowableHolderException(ex);
              }
            }
            else {
              // A normal return value: will lead to a commit.
              throwableHolder.throwable = ex;
              return null;
            }
          }
          finally {
            cleanupTransactionInfo(txInfo);
          }
        });
 
        // Check result state: It might indicate a Throwable to rethrow.
        if (throwableHolder.throwable != null) {
          throw throwableHolder.throwable;
        }
        return result;
      }
      catch (ThrowableHolderException ex) {
        throw ex.getCause();
      }
      catch (TransactionSystemException ex2) {
        if (throwableHolder.throwable != null) {
          logger.error("Application exception overridden by commit exception", throwableHolder.throwable);
          ex2.initApplicationException(throwableHolder.throwable);
        }
        throw ex2;
      }
      catch (Throwable ex2) {
        if (throwableHolder.throwable != null) {
          logger.error("Application exception overridden by commit exception", throwableHolder.throwable);
        }
        throw ex2;
      }
    }
  }

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