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Spring中@Transactional用法详细介绍
引言： 在spring中@Transactional提供一种控制事务管理的快捷手段，但是很多人都只是@Transactional简单使用，并未深入了解，其各个配置项的使用方法，本文将深入讲解各个配置项的使用。
1. @Transactional的定义
Spring中的@Transactional基于动态代理的机制，提供了一种透明的事务管理机制，方便快捷解决在开发中碰到的问题。在现实中，实际的问题往往比我们预期的要复杂很多，这就要求对@Transactional有深入的了解，以来应对复杂问题。
首先我们来看看@Transactional的代码定义：
@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Transactional {
/**
* A qualifier value for the specified transaction.
* <p>May be used to determine the target transaction manager,
* matching the qualifier value (or the bean name) of a specific
* {@link org.springframework.transaction.PlatformTransactionManager}
* bean definition.
*/
String value() default "";
/**
* The transaction propagation type.
* Defaults to {@link Propagation#REQUIRED}.
* @see org.springframework.transaction.interceptor.TransactionAttribute#getPropagationBehavior()
*/
Propagation propagation() default Propagation.REQUIRED;
/**
* The transaction isolation level.
* Defaults to {@link Isolation#DEFAULT}.
* @see org.springframework.transaction.interceptor.TransactionAttribute#getIsolationLevel()
*/
Isolation isolation() default Isolation.DEFAULT;
/**
* The timeout for this transaction.
* Defaults to the default timeout of the underlying transaction system.
* @see org.springframework.transaction.interceptor.TransactionAttribute#getTimeout()
*/
int timeout() default TransactionDefinition.TIMEOUT_DEFAULT;
/**
* {@code true} if the transaction is read-only.
* Defaults to {@code false}.
* <p>This just serves as a hint for the actual transaction subsystem;
* it will <i>not necessarily</i> cause failure of write access attempts.
* A transaction manager which cannot interpret the read-only hint will
* <i>not</i> throw an exception when asked for a read-only transaction.
* @see org.springframework.transaction.interceptor.TransactionAttribute#isReadOnly()
*/
boolean readOnly() default false;
/**
* Defines zero (0) or more exception {@link Class classes}, which must be a
* subclass of {@link Throwable}, indicating which exception types must cause
* a transaction rollback.
* <p>This is the preferred way to construct a rollback rule, matching the
* exception class and subclasses.
* <p>Similar to {@link org.springframework.transaction.interceptor.RollbackRuleAttribute#RollbackRuleAttribute(Class clazz)}
*/
Class<? extends Throwable>[] rollbackFor() default {};
/**
* Defines zero (0) or more exception names (for exceptions which must be a
* subclass of {@link Throwable}), indicating which exception types must cause
* a transaction rollback.
* <p>This can be a substring, with no wildcard support at present.
* A value of "ServletException" would match
* {@link javax.servlet.ServletException} and subclasses, for example.
* <p><b>NB: </b>Consider carefully how specific the pattern is, and whether
* to include package information (which isn't mandatory). For example,
* "Exception" will match nearly anything, and will probably hide other rules.
* "java.lang.Exception" would be correct if "Exception" was meant to define
* a rule for all checked exceptions. With more unusual {@link Exception}
* names such as "BaseBusinessException" there is no need to use a FQN.
* <p>Similar to {@link org.springframework.transaction.interceptor.RollbackRuleAttribute#RollbackRuleAttribute(String exceptionName)}
*/
String[] rollbackForClassName() default {};
/**
* Defines zero (0) or more exception {@link Class Classes}, which must be a
* subclass of {@link Throwable}, indicating which exception types must <b>not</b>
* cause a transaction rollback.
* <p>This is the preferred way to construct a rollback rule, matching the
* exception class and subclasses.
* <p>Similar to {@link org.springframework.transaction.interceptor.NoRollbackRuleAttribute#NoRollbackRuleAttribute(Class clazz)}
*/
Class<? extends Throwable>[] noRollbackFor() default {};
/**
* Defines zero (0) or more exception names (for exceptions which must be a
* subclass of {@link Throwable}) indicating which exception types must <b>not</b>
* cause a transaction rollback.
* <p>See the description of {@link #rollbackForClassName()} for more info on how
* the specified names are treated.
* <p>Similar to {@link org.springframework.transaction.interceptor.NoRollbackRuleAttribute#NoRollbackRuleAttribute(String exceptionName)}
*/
String[] noRollbackForClassName() default {};
}
基于源代码，我们可以发现圫ATION_NESTED : uses a single physical transaction with multiple
savepoints that it can roll back to. Such partial rollbacks allow an
inner transaction scope to trigger a rollback for its scope, with the outer
transaction being able to continue the physical transaction despite some operations
having been rolled back. This setting is typically mapped onto JDBC savepoints, so will
only work with JDBC resource transactions.
NESTED的事务，基于单一的事务来管理，提供了多个保存点。这种多个保存点的机制允许内部事务的变更触发外部事务的回滚。而外部事务在混滚之后，仍能继续进行事务处理，即使部分操作已经被混滚。 由于这个设置基于JDBC的保存点，所以只能工作在JDBC的机制智商。
由此可知， 两者都是事务嵌套，不同之处在于，内外事务之间是否存在彼此之间的影响；NESTED之间会受到影响，而产生部分回滚，而REQUIRED_NEW则是独立的。
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