********TransactionDefinition 接口定义*******************
/**   * Support a current transaction, create a new one if none exists.   * Analogous to EJB transaction attribute of the same name.   * 

This is typically the default setting of a transaction definition.          */         int PROPAGATION_REQUIRED = 0;            /**          * Support a current transaction, execute non-transactionally if none exists.          * Analogous to EJB transaction attribute of the same name.          *

Note: For transaction managers with transaction synchronization,          * PROPAGATION_SUPPORTS is slightly different from no transaction at all,          * as it defines a transaction scopp 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          */         int PROPAGATION_SUPPORTS = 1;            /**          * Support a current transaction, throw an exception if none exists.          * Analogous to EJB transaction attribute of the same name.          */         int PROPAGATION_MANDATORY = 2;            /**          * Create a new transaction, suspend the current transaction if one exists.          * Analogous to EJB transaction attribute of the same name.          *

Note: Actual transaction suspension will not work on out-of-the-box          * on all transaction managers. This in particular applies to JtaTransactionManager,          * which requires the javax.transaction.TransactionManager to be          * made available it to it (which is server-specific in standard J2EE).          * @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager          */         int PROPAGATION_REQUIRES_NEW = 3;            /**          * Execute non-transactionally, suspend the current transaction if one exists.          * Analogous to EJB transaction attribute of the same name.          *

Note: Actual transaction suspension will not work on out-of-the-box          * on all transaction managers. This in particular applies to JtaTransactionManager,          * which requires the javax.transaction.TransactionManager to be          * made available it to it (which is server-specific in standard J2EE).          * @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager          */         int PROPAGATION_NOT_SUPPORTED = 4;            /**          * Execute non-transactionally, throw an exception if a transaction exists.          * Analogous to EJB transaction attribute of the same name.          */         int PROPAGATION_NEVER = 5;            /**          * Execute within a nested transaction if a current transaction exists,          * behave like PROPAGATION_REQUIRED else. There is no analogous feature in EJB.          *

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          */         int PROPAGATION_NESTED = 6;   

ServiceA {   /**  * 事务属性配置为 PROPAGATION_REQUIRED  */  void methodA() {   ServiceB.methodB();   }   }   ServiceB {   /**  * 事务属性配置为 PROPAGATION_REQUIRED  */    void methodB() {   }   }