该类是每层事务的抽象，并且是一个链表结构，一个节点表示一层事务，这链表（这多层事务）对应着同一个TransactionInterceptor和同一个PlatformTransactionManager

由于该类是一个protected修饰的TransactionAspectSupport的内部类，所以如果自己想查看执行事务时候，当前事务的属性，应该通过反射机制调用currentTransactionInfo方法才可以，本文后续会有调试代码

该类是TransactionAspectSupport类的内部类，有下面几个属性

@Nullable
private final PlatformTransactionManager transactionManager;
@Nullable
private final TransactionAttribute transactionAttribute;

private final String joinpointIdentification;
@Nullable
private TransactionStatus transactionStatus;
@Nullable
private TransactionInfo oldTransactionInfo;

其中​​transactionManager​​​，​​transactionAttribute​​​，​​transactionStatus​​，都已经介绍过，本文着重阐述joinpointIdentification和oldTransactionInfo

一：joinpointIdentification
要执行事务的方法的全限定名，字符串形式
二：oldTransactionInfo
表示在哪个事务中开启的事务，比如A事务里有事务B，那么此时就有两个TransactionInfo，后一个TransactionInfo（B）包含着一个前一个TransactionInfo（A）的引用，这个指针用oldTransactionInfo属性来表示

下面是证明oldTransactionInfo过程，不爱看的不看
创建第一个事务类Create1

@Component
public class Creater1 {
  @Autowired
  JdbcTemplate jdbcTemplate;
  @Autowired
  Creater2 creater2;

  @Transactional(rollbackFor = Exception.class)
  public void create() throws Exception {
    jdbcTemplate.update("insert into t1(value) values ('养1只垂耳兔')");
    Class<TransactionAspectSupport> clazz = TransactionAspectSupport.class;
    Method m = clazz.getDeclaredMethod("currentTransactionInfo");
    m.setAccessible(true);
    Object o = m.invoke(clazz);
    System.out.println(o);// 将断点打到这里观察oldTransactionInfo属性
    creater2.create();
  }
}

创建第二个事务类Create2，用来在Create1中嵌套

@Component
public class Creater2 {
  @Autowired
  JdbcTemplate jdbcTemplate;
  @Transactional(rollbackFor = Exception.class, propagation = Propagation.REQUIRED)
  public void create() throws Exception {
    jdbcTemplate.update("insert into t1(value) values ('养2只垂耳兔')");
    Class<TransactionAspectSupport> clazz = TransactionAspectSupport.class;
    Method m = clazz.getDeclaredMethod("currentTransactionInfo");
    m.setAccessible(true);
    Object o = m.invoke(clazz);// 将断点打到这里观察oldTransactionInfo属性
    System.out.println(o);
  }
}

创建Main方法，并且运行，查看断点处，可发现oldTransactionInfo的值，正好一个事务对应一个info

@Configuration
@EnableTransactionManagement
public class TestMain {

  @Bean
  public DataSource dataSource() {
    HikariDataSource ds = new HikariDataSource();
    ds.setJdbcUrl("jdbc:mysql://localhost:3306/swttest?serverTimezone=UTC&&useSSL=false");
    ds.setUsername("root");
    ds.setPassword("123456");
    return ds;
  }

  @Bean
  public JdbcTemplate jdbcTemplate() {
    JdbcTemplate jdbc = new JdbcTemplate();
    jdbc.setDataSource(dataSource());
    return jdbc;
  }

  @Bean
  public PlatformTransactionManager platformTransactionManager() {
    DataSourceTransactionManager manager = new DataSourceTransactionManager(dataSource());
    return manager;
  }

  public static void main(String[] args) throws Throwable {
    // 依赖容器的话必须要开启@EnableTransactionManagement注解，表示告诉spring我要使用事务
    AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(
        "基础包名");
    Creater1 tt = ctx.getBean(Creater1.class);
    tt.create();
  }
}