异常信息：支持当前事务，如果不存在则抛出异常。事务被回滚，因为它被标记为仅回滚

org.springframework.transaction.UnexpectedRollbackException: Transaction rolled back because it has been marked as rollback-onlyat org.springframework.transaction.support.AbstractPlatformTransactionManager.processRollback(AbstractPlatformTransactionManager.java:873)at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:710)at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:533)at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:304)at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:98)

Spring事务传播机制：可以查看如下枚举
总结如下：

• PROPAGATION_REQUIRED：如果当前没有事务，就新建一个事务，如果已经存在一个事务，就加入到这个事务中。默认策略
• PROPAGATION_SUPPORTS：支持当前事务，如果当前没有事务，就以非事务方式执行。
• PROPAGATION_MANDATORY：使用当前的事务，如果当前没有事务，就抛出异常。
• PROPAGATION_REQUIRES_NEW：新建事务，如果当前存在事务，把当前事务挂起。
• PROPAGATION_NOT_SUPPORTED：以非事务方式执行操作，如果当前存在事务，就把当前事务挂起。
• PROPAGATION_NEVER：以非事务方式执行，如果当前存在事务，则抛出异常。
• PROPAGATION_NESTED：如果当前存在事务，则在嵌套事务内执行。如果当前没有事务，则执行与PROPAGATION_REQUIRED类似的操作。
  nested 的子异常抛出 如果被catch 外部插入成功 nested 的子异常抛出 如果不被catch 外部插入失败
  nested外面异常抛出 nest内部插入成功 nest也会跟着回滚

/** Copyright 2002-2018 the original author or authors.** Licensed under the Apache License, Version 2.0 (the "License");* you may not use this file except in compliance with the License.* You may obtain a copy of the License at**      https://www.apache.org/licenses/LICENSE-2.0** Unless required by applicable law or agreed to in writing, software* distributed under the License is distributed on an "AS IS" BASIS,* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.* See the License for the specific language governing permissions and* limitations under the License.*/package org.springframework.transaction.annotation;import org.springframework.transaction.TransactionDefinition;/*** Enumeration that represents transaction propagation behaviors for use* with the {@link Transactional} annotation, corresponding to the* {@link TransactionDefinition} interface.** @author Colin Sampaleanu* @author Juergen Hoeller* @since 1.2*/
public enum Propagation {/*** Support a current transaction, create a new one if none exists.* Analogous to EJB transaction attribute of the same name.* 
This is the default setting of a transaction annotation.*/REQUIRED(TransactionDefinition.PROPAGATION_REQUIRED),/*** Support a current transaction, execute non-transactionally if none exists.* 支持当前事务，如果不存在则以非事务方式执行。* 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 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.* 注意:对于具有事务同步的事务管理器，PROPAGATION_SUPPORTS与完全没有事务略有不同因为它定义了同步将应用的事务范围因此，相同的资源(JDBC连接，Hibernate Sess将为整个指定范围共享。注意，这取决于事务管理器的实际同步配置。* @see org.springframework.transaction.support.AbstractPlatformTransactionManager#setTransactionSynchronization*/SUPPORTS(TransactionDefinition.PROPAGATION_SUPPORTS),/*** Support a current transaction, throw an exception if none exists.* 支持当前事务，如果不存在则抛出异常。* Analogous to EJB transaction attribute of the same name.*/MANDATORY(TransactionDefinition.PROPAGATION_MANDATORY),/*** Create a new transaction, and suspend the current transaction if one exists.* 创建一个新事务，如果存在当前事务，则挂起当前事务。* Analogous to the EJB transaction attribute of the same name.* 
NOTE: 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 to it (which is server-specific in standard Java EE).* @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager*/REQUIRES_NEW(TransactionDefinition.PROPAGATION_REQUIRES_NEW),/*** Execute non-transactionally, suspend the current transaction if one exists.* 以非事务方式执行，如果存在当前事务，则暂停当前事务。* Analogous to EJB transaction attribute of the same name.* 
NOTE: 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 to it (which is server-specific in standard Java EE).* @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager*/NOT_SUPPORTED(TransactionDefinition.PROPAGATION_NOT_SUPPORTED),/*** Execute non-transactionally, throw an exception if a transaction exists.* 以非事务方式执行，如果存在事务则抛出异常。* Analogous to EJB transaction attribute of the same name.*/NEVER(TransactionDefinition.PROPAGATION_NEVER),/*** Execute within a nested transaction if a current transaction exists,* 如果当前事务存在，则在嵌套事务中执行，* behave like PROPAGATION_REQUIRED else. There is no analogous feature in EJB.* 行为类似于PROPAGATION_REQUIRED else。EJB中没有类似的特性。* 
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*/NESTED(TransactionDefinition.PROPAGATION_NESTED);private final int value;Propagation(int value) {this.value = value;}public int value() {return this.value;}}

spring事务默认的传播行为：
@Transactional 等于 @Transactional(propagation=Propagation.REQUIRED)

发生异常的场景描述：
在使用Spring事务时，在一个事务A中又开了一个事务B（即存在嵌套事务），当事务B发生异常时，将异常catch后事务B会进行回滚操作，若此时异常被直接吃掉（即事务A无法得知发生过异常），则事务A会抛出如上异常。

serviceA有事务 @TransactionalserviceB有事务 @Transactional有@TransactionalServiceA -> {ServiceAtry {@Transactional()ServiceB{异常 BusinessException事务回滚}} catch (Exception e) {}} 

原因：
因为ServiceB的传播属性设置为PROPAGATION_REQUIRED，PROPAGATION_REQUIRED的意思是，当前有事务，则使用当前事务，当前无事务则创建事务。由于ServiceA的传播属性也为PROPAGATION_REQUIRED，所以ServiceA会创建一个事务，然后ServiceB与ServiceA使用同一个事务，ServiceB出现异常后，将当前事务标志位回滚，由于在ServiceA中做了trycatch处理，程序没有终止而是继续往下走，当事务commit时，check状态，发现，需要事务回滚，所以才会出现不可预知的事务异常:因为事务被标志位回滚，所以事务回滚。
也就是说:ServiceA与ServiceB共用一个事务，ServiceB将事务标志为回滚，ServiceA中commit这个事务，然后，出现事务已经被标志回滚（ServiceB标志的）的异常信息。

解决方案
情况1：ServiceA与ServiceB在逻辑上不应该属于同一个事务，那么将ServiceB的事务传播属性修改为PROPAGATION_REQUIRES_NEW，这样，执行ServiceB时，会创建一个新的事务，不影响ServiceA中的事务。

情况2：业务A与业务B在业务逻辑上就应该属于同一个事务，那么将ServiceA中的try catch去掉

情况3：业务A与业务B在业务逻辑上就应该属于同一个事务，但是ServiceB的失败与否不能影响ServiceA的事务提交，那么仍然在ServiceA中try catch ServiceB,并将ServiceB设置为PROPAGATION_NESTED，它的意思是，ServiceB是一个子事务，有一个savepoint，失败时会回滚到savepoint，不影响ServiceA，如果成功则A、B一起提交，A与B都是一个事务，只是B是一个子事务。
情况4：业务A 有无事务无影响 去掉业务A的@Transactional