SpringBoot中事务执行原理分析（六）

public interface TransactionSynchronization extends Flushable {
  // 正确提交时的完成状态
  int STATUS_COMMITTED = 0;
  // 正确回滚时的完成状态
  int STATUS_ROLLED_BACK = 1;
//启发式混合完成或系统错误情况下
  int STATUS_UNKNOWN = 2;
   //挂起同步，如果TransactionSynchronizationManager 有管理资源则接触资源绑定
  default void suspend() {
  }
   //恢复同步，如果事务同步管理器有管理资源则重新绑定
  default void resume() {
  }
//   如果适用，将底层会话刷新到数据存储：例如，Hibernate/JPA会话。
  @Override
  default void flush() {
  }
   //在事务提交前触发 RuntimeException 将会传播给调用方，
   //不要在此处抛出TransactionException的子类
  default void beforeCommit(boolean readOnly) {
  }
   //在事务提交/回滚前触发
  default void beforeCompletion() {
  }
   //事务成功提交后触发
  default void afterCommit() {
  }
   //在事务提交/回滚后触发
  default void afterCompletion(int status) {
  }
}

private static final class SqlSessionSynchronization extends TransactionSynchronizationAdapter {
//持有SqlSession
  private final SqlSessionHolder holder;
  private final SqlSessionFactory sessionFactory;
  private boolean holderActive = true;
  public SqlSessionSynchronization(SqlSessionHolder holder, SqlSessionFactory sessionFactory) {
    notNull(holder, "Parameter 'holder' must be not null");
    notNull(sessionFactory, "Parameter 'sessionFactory' must be not null");
    this.holder = holder;
    this.sessionFactory = sessionFactory;
  }
   //获取其执行顺序
  @Override
  public int getOrder() {
    // order right before any Connection synchronization
    return DataSourceUtils.CONNECTION_SYNCHRONIZATION_ORDER - 1;
  }
   // 挂起，实际是解除资源绑定，这里key就是this.sessionFactory
  @Override
  public void suspend() {
    if (this.holderActive) {
      LOGGER.debug(() -> "Transaction synchronization suspending SqlSession [" + this.holder.getSqlSession() + "]");
      TransactionSynchronizationManager.unbindResource(this.sessionFactory);
    }
  }
   //恢复，实际是绑定资源，key -sessionFactory ,value - holder
  @Override
  public void resume() {
    if (this.holderActive) {
      LOGGER.debug(() -> "Transaction synchronization resuming SqlSession [" + this.holder.getSqlSession() + "]");
      TransactionSynchronizationManager.bindResource(this.sessionFactory, this.holder);
    }
  }
//核心是触发sqlsession的commit
  @Override
  public void beforeCommit(boolean readOnly) {
    // Connection commit or rollback will be handled by ConnectionSynchronization or
    // DataSourceTransactionManager.
    // But, do cleanup the SqlSession / Executor, including flushing BATCH statements so
    // they are actually executed.
    // SpringManagedTransaction will no-op the commit over the jdbc connection
    // TODO This updates 2nd level caches but the tx may be rolledback later on!
    //如果线程本地对象actualTransactionActive 储存资源不为null
    if (TransactionSynchronizationManager.isActualTransactionActive()) {
      try {
      //触发sqlsession的commit，将会清理本地缓存，flushStatements
        this.holder.getSqlSession().commit(); 
      } catch (PersistenceException p) {
        if (this.holder.getPersistenceExceptionTranslator() != null) {
          DataAccessException translated = this.holder.getPersistenceExceptionTranslator()
              .translateExceptionIfPossible(p);
          if (translated != null) {
            throw translated;
          }
        }
        throw p;
      }
    }
  }
//如果referenceCount小于1，则关闭SqlSession，重置holder、holderActive 
  @Override
  public void beforeCompletion() {
    // Issue #18 Close SqlSession and deregister it now
    // because afterCompletion may be called from a different thread
    //也就是referenceCount小于1
    if (!this.holder.isOpen()) {
  //解除资源绑定，key是sessionFactory
      TransactionSynchronizationManager.unbindResource(sessionFactory);
      //重置holderActive为false
      this.holderActive = false;
     //触发sqlsession的close方法
      this.holder.getSqlSession().close();
    }
  }
   //如果holderActive为true，则关闭SqlSession，重置holder、holderActive 
  @Override
  public void afterCompletion(int status) {
  //如果holderActive为true
    if (this.holderActive) {
      // afterCompletion may have been called from a different thread
      // so avoid failing if there is nothing in this one
          //尝试解除资源绑定
      TransactionSynchronizationManager.unbindResourceIfPossible(sessionFactory);
     //重置holderActive为false
      this.holderActive = false;
      //触发sqlsession的close方法
      this.holder.getSqlSession().close();
    }
    this.holder.reset();
  }
}