Spring注解（四）——————Spring事务原理

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以下测试的源码地址：https://github.com/877148107/Spring-Annotation

• @EnableTransactionManagement开启基于注解的事务功能

@ComponentScan({"com.spring.annotation.dao","com.spring.annotation.service"})
@EnableTransactionManagement
@Configuration
public class MyTxConfig {

    @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{
        JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource());
        return jdbcTemplate;
    }

    @Bean
    public PlatformTransactionManager platformTransactionManager() throws  Exception{
        return new DataSourceTransactionManager(dataSource());
    }
}

• @EnableTransactionManagement原理：

1. @EnableTransactionManagement利用TransactionManagementConfigurationSelector给容器中导入两个组件：

   @Target(ElementType.TYPE)
   @Retention(RetentionPolicy.RUNTIME)
   @Documented
   @Import(TransactionManagementConfigurationSelector.class)
   public @interface EnableTransactionManagement {
   
   	/**
   	 * Indicate whether subclass-based (CGLIB) proxies are to be created ({@code true}) as
   	 * opposed to standard Java interface-based proxies ({@code false}). The default is
   	 * {@code false}. <strong>Applicable only if {@link #mode()} is set to
   	 * {@link AdviceMode#PROXY}</strong>.
   	 * <p>Note that setting this attribute to {@code true} will affect <em>all</em>
   	 * Spring-managed beans requiring proxying, not just those marked with
   	 * {@code @Transactional}. For example, other beans marked with Spring's
   	 * {@code @Async} annotation will be upgraded to subclass proxying at the same
   	 * time. This approach has no negative impact in practice unless one is explicitly
   	 * expecting one type of proxy vs another, e.g. in tests.
   	 */
   	boolean proxyTargetClass() default false;
   
   	/**
   	 * Indicate how transactional advice should be applied. The default is
   	 * {@link AdviceMode#PROXY}.
   	 * @see AdviceMode
   	 */
   	AdviceMode mode() default AdviceMode.PROXY;
   
   	/**
   	 * Indicate the ordering of the execution of the transaction advisor
   	 * when multiple advices are applied at a specific joinpoint.
   	 * The default is {@link Ordered#LOWEST_PRECEDENCE}.
   	 */
   	int order() default Ordered.LOWEST_PRECEDENCE;
   
   }
   

   1. AutoProxyRegistrar

   2. ProxyTransactionManagementConfiguration

1. AutoProxyRegistrar作用：

   1. 给容器中注册一个InfrastructureAdvisorAutoProxyCreator组件

   2. InfrastructureAdvisorAutoProxyCreator也是一个后置处理器，利用后置处理机制在对象创建完成后，返回一个代理对象，代理对象执行方法利用拦截器链进行调用

 

1. ProxyTransactionManagementConfiguration作用：

   1. 给容器中注册事务增强器

   2. 事务增强器要用事务注解的信息，AnnotationTransactionAttributeSource解析事务注解

   3. 事务拦截器transactionInterceptor()，TransactionInterceptor保存了事务属性的信息，还有事务管理器，实际上它是一个方法拦截器MethodInterceptor

transactionInterceptor()在目标方法执行的时候：实际上就是执行拦截器链

1. 先获取事务相关的属性

2. 再获取PlatformTransactionManager，如果事先没有添加，那么会从容器中按照类型获取

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