在spring的事务管理中,我们可以使用@Transactional这一annotation来对事务进行声明式的设定。具体而言,就是在类或者方法前添加@Transactional并传入属性参数以获取所需要的Transaction特性。Spring中的@Transactional有5个属性:Propagation、Isolation、Rollback Rules、Timeout和Read-Only,其中Propagation属性定义了Transaction的边界 — 是否使用Transaction、在Transaction已存在的情况下如何表现等。
在service类前加上@Transactional,声明这个service所有方法需要事务管理。每一个业务方法开始时都会打开一个事务。
Spring默认情况下会对运行期例外(RunTimeException)进行事务回滚。这个例外是unchecked
如果遇到checked意外就不回滚。
如何改变默认规则:
1 让checked例外也回滚:在整个方法前加上 @Transactional(rollbackFor=Exception.class)
2 让unchecked例外不回滚: @Transactional(notRollbackFor=RunTimeException.class)
3 不需要事务管理的(只查询的)方法:@Transactional(propagation=Propagation.NOT_SUPPORTED)
在整个方法运行前就不会开启事务
还可以加上:@Transactional(propagation=Propagation.NOT_SUPPORTED,readOnly=true),这样就做成一个只读事务,可以提高效率。
各种属性的意义:
REQUIRED:业务方法需要在一个容器里运行。如果方法运行时,已经处在一个事务中,那么加入到这个事务,否则自己新建一个新的事务。
NOT_SUPPORTED:声明方法不需要事务。如果方法没有关联到一个事务,容器不会为他开启事务,如果方法在一个事务中被调用,该事务会被挂起,调用结束后,原先的事务会恢复执行。
REQUIRESNEW:不管是否存在事务,该方法总汇为自己发起一个新的事务。如果方法已经运行在一个事务中,则原有事务挂起,新的事务被创建。
MANDATORY:该方法只能在一个已经存在的事务中执行,业务方法不能发起自己的事务。如果在没有事务的环境下被调用,容器抛出例外。
SUPPORTS:该方法在某个事务范围内被调用,则方法成为该事务的一部分。如果方法在该事务范围外被调用,该方法就在没有事务的环境下执行。
NEVER:该方法绝对不能在事务范围内执行。如果在就抛例外。只有该方法没有关联到任何事务,才正常执行。
NESTED:如果一个活动的事务存在,则运行在一个嵌套的事务中。如果没有活动事务,则按REQUIRED属性执行。它使用了一个单独的事务,这个事务拥有多个可以回滚的保存点。内部事务的回滚不会对外部事务造成影响。它只对DataSourceTransactionManager事务管理器起效。
观察以下两个定义了@Transactional的方法,innerMethod()模拟了Transaction已经存在的情况,outMethod()则模拟了不存在已定义Transaction的情况:
@Transactional
public void outMethod() {
exampleDAO.doSomething();
innerMethod();
}
@Transactional
public void innerMethod() {
exampleDAO.doElse();
}
对于这两个方法,定义不同的Propagation属性值所产生的效果如下(Propagation.NESTED的情况较为复杂,在此忽略):
Propagation属性 |
outMethod |
innerMethod |
Propagation.MANDATORY |
.抛出异常 |
.在outMethod的Transaction中运行 |
Propagation.NEVER |
.不在Transaction中运行 |
.抛出异常 |
Propagation.NOT_SUPPORTED |
.不在Transaction中运行 |
.outMethod的Transaction暂停直至innerMethod执行完毕 |
Propagation.REQUIRED ( 默认值 ) |
.新开一个Transaction并在其中运行 |
.在outMethod的Transaction中运行 |
Propagation.REQUIRES_NEW |
.新开一个Transaction并在其中运行 |
.outMethod的Transaction暂停直至innerMethod中新开的Transaction执行完毕 |
Propagation.SUPPORTS |
.不在Transaction中运行 |
.在outMethod的Transaction中运行 |
@Transactional的代码定义:
-
@Target({ElementType.METHOD, ElementType.TYPE})
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@Retention(RetentionPolicy.RUNTIME)
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@Inherited
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@Documented
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public @interface Transactional {
-
-
/**
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* A qualifier value for the specified transaction.
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* <p>May be used to determine the target transaction manager,
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* matching the qualifier value (or the bean name) of a specific
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* {@link org.springframework.transaction.PlatformTransactionManager}
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* bean definition.
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*/
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String value() default "";
-
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/**
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* The transaction propagation type.
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* Defaults to {@link Propagation#REQUIRED}.
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* @see org.springframework.transaction.interceptor.TransactionAttribute#getPropagationBehavior()
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*/
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Propagation propagation() default Propagation.REQUIRED;
-
-
/**
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* The transaction isolation level.
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* Defaults to {@link Isolation#DEFAULT}.
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* @see org.springframework.transaction.interceptor.TransactionAttribute#getIsolationLevel()
-
*/
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Isolation isolation() default Isolation.DEFAULT;
-
-
/**
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* The timeout for this transaction.
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* Defaults to the default timeout of the underlying transaction system.
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* @see org.springframework.transaction.interceptor.TransactionAttribute#getTimeout()
-
*/
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int timeout() default TransactionDefinition.TIMEOUT_DEFAULT;
-
-
/**
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* {@code true} if the transaction is read-only.
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* Defaults to {@code false}.
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* <p>This just serves as a hint for the actual transaction subsystem;
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* it will <i>not necessarily</i> cause failure of write access attempts.
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* A transaction manager which cannot interpret the read-only hint will
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* <i>not</i> throw an exception when asked for a read-only transaction.
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* @see org.springframework.transaction.interceptor.TransactionAttribute#isReadOnly()
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*/
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boolean readOnly() default false;
-
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/**
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* Defines zero (0) or more exception {@link Class classes}, which must be a
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* subclass of {@link Throwable}, indicating which exception types must cause
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* a transaction rollback.
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* <p>This is the preferred way to construct a rollback rule, matching the
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* exception class and subclasses.
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* <p>Similar to {@link org.springframework.transaction.interceptor.RollbackRuleAttribute#RollbackRuleAttribute(Class clazz)}
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*/
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Class<? extends Throwable>[] rollbackFor() default {};
-
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/**
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* Defines zero (0) or more exception names (for exceptions which must be a
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* subclass of {@link Throwable}), indicating which exception types must cause
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* a transaction rollback.
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* <p>This can be a substring, with no wildcard support at present.
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* A value of "ServletException" would match
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* {@link javax.servlet.ServletException} and subclasses, for example.
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* <p><b>NB: </b>Consider carefully how specific the pattern is, and whether
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* to include package information (which isn't mandatory). For example,
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* "Exception" will match nearly anything, and will probably hide other rules.
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* "java.lang.Exception" would be correct if "Exception" was meant to define
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* a rule for all checked exceptions. With more unusual {@link Exception}
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* names such as "BaseBusinessException" there is no need to use a FQN.
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* <p>Similar to {@link org.springframework.transaction.interceptor.RollbackRuleAttribute#RollbackRuleAttribute(String exceptionName)}
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*/
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String[] rollbackForClassName() default {};
-
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/**
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* Defines zero (0) or more exception {@link Class Classes}, which must be a
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* subclass of {@link Throwable}, indicating which exception types must <b>not</b>
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* cause a transaction rollback.
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* <p>This is the preferred way to construct a rollback rule, matching the
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* exception class and subclasses.
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* <p>Similar to {@link org.springframework.transaction.interceptor.NoRollbackRuleAttribute#NoRollbackRuleAttribute(Class clazz)}
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*/
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Class<? extends Throwable>[] noRollbackFor() default {};
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/**
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* Defines zero (0) or more exception names (for exceptions which must be a
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* subclass of {@link Throwable}) indicating which exception types must <b>not</b>
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* cause a transaction rollback.
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* <p>See the description of {@link #rollbackForClassName()} for more info on how
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* the specified names are treated.
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* <p>Similar to {@link org.springframework.transaction.interceptor.NoRollbackRuleAttribute#NoRollbackRuleAttribute(String exceptionName)}
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*/
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String[] noRollbackForClassName() default {};
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}
基于源代码,我们可以发现在@Transactional,原来有这么多的属性可以进行配置,从而达到复杂应用控制的目的。
http://www./articles/6rEjAv
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