REQUIRED

   /**
     * Support a current transaction, create a new one if none exists.
     * Analogous to EJB transaction attribute of the same name.
     * <p>This is the default setting of a transaction annotation.
     */

必须有一个事务，如果当前已存在则用当前的，如果不存在则新建一个事务

SUPPORTS

   /**
     * Support a current transaction, execute non-transactionally if none exists.
     * Analogous to EJB transaction attribute of the same name.
     * <p>Note: For transaction managers with transaction synchronization,
     * PROPAGATION_SUPPORTS is slightly different from no transaction at all,
     * as it defines a transaction scope that synchronization will apply for.
     * As a consequence, the same resources (JDBC Connection, Hibernate Session, etc)
     * will be shared for the entire specified scope. Note that this depends on
     * the actual synchronization configuration of the transaction manager.
     * @see org.springframework.transaction.support.AbstractPlatformTransactionManager#setTransactionSynchronization
     */

使用当前事物，如果当前则以无事务模式运行

MANDATORY

   /**
     * Support a current transaction, throw an exception if none exists.
     * Analogous to EJB transaction attribute of the same name.
     */

表示强制需要一个事务，如果不存事务则抛出异常

REQUIRES_NEW

   /**
     * Create a new transaction, and suspend the current transaction if one exists.
     * Analogous to the EJB transaction attribute of the same name.
     * <p><b>NOTE:</b> Actual transaction suspension will not work out-of-the-box
     * on all transaction managers. This in particular applies to
     * {@link org.springframework.transaction.jta.JtaTransactionManager},
     * which requires the {@code javax.transaction.TransactionManager} to be
     * made available it to it (which is server-specific in standard Java EE).
     * @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager
     */

每次都创建一个新的事务，如果当前存在事务则挂起当前事务运行新事务，两个事务互相独立，新事物回滚也不会影响外部事务

NOT_SUPPORTED

   /**
     * Execute non-transactionally, suspend the current transaction if one exists.
     * Analogous to EJB transaction attribute of the same name.
     * <p><b>NOTE:</b> Actual transaction suspension will not work out-of-the-box
     * on all transaction managers. This in particular applies to
     * {@link org.springframework.transaction.jta.JtaTransactionManager},
     * which requires the {@code javax.transaction.TransactionManager} to be
     * made available it to it (which is server-specific in standard Java EE).
     * @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager
     */

已非事务模式运行，如果当前存在事务则挂起当前事务

NEVER

   /**
     * Execute non-transactionally, throw an exception if a transaction exists.
     * Analogous to EJB transaction attribute of the same name.
     */

从不需要事务，如果当前存在事务则抛出异常，刚好与 MANDATORY 相反

NESTED

    /**
     * Execute within a nested transaction if a current transaction exists,
     * behave like PROPAGATION_REQUIRED else. There is no analogous feature in EJB.
     * <p>Note: Actual creation of a nested transaction will only work on specific
     * transaction managers. Out of the box, this only applies to the JDBC
     * DataSourceTransactionManager when working on a JDBC 3.0 driver.
     * Some JTA providers might support nested transactions as well.
     * @see org.springframework.jdbc.datasource.DataSourceTransactionManager
     */

嵌入式事务模式，与PROPAGATION_REQUIRED相似，如果没有就新建，如果有适用当前事务，但是NESTED具体当前事务多个保存点，可以部分回滚。仅适用于JDBC事务管理，内部可以独立回滚并且不影响外部。