Spring中@Transactional用法深度分析之一

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 {};

}

2.  使用@Transactional的Spring配置

     为了使用基于@Transactional的事务管理，需要在Spring中进行如下的配置：

    <beans:bean id="transactionManager"
		class="org.springframework.orm.jpa.JpaTransactionManager">
		<beans:property name="dataSource" ref="dataSource" />
		<beans:property name="entityManagerFactory" ref="entityManagerFactory" />
	</beans:bean>

	<!-- 声明使用注解式事务 -->
	<tx:annotation-driven transaction-manager="transactionManager" />

    <annotation-driven>标签的声明，则是在Spring内部启用@Transactional来进行事务管理，类似开关之类的声明。

3.  @Transactional之value

    value这里主要用来指定不同的事务管理器；主要用来满足在同一个系统中，存在不同的事务管理器。比如在Spring中，声明了两种事务管理器txManager1, txManager2.

然后，用户可以根据这个参数来根据需要指定特定的txManager.

   那有同学会问什么情况下会存在多个事务管理器的情况呢？ 比如在一个系统中，需要访问多个数据源或者多个数据库，则必然会配置多个事务管理器的。

4.   @Transactional之propagation

      Propagation支持7种不同的传播机制：

•  REQUIRED

•  SUPPORTS： 

•  MANDATORY：

•  REQUIRES_NEW

•  NOT_SUPPORTED

• NEVER：

•  NESTED：

          如果一个活动的事务存在,则运行在一个嵌套的事务中.如果没有活动的事务,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证点.内部事务回滚不会对外部事务造成影响, 它只对DataSourceTransactionManager 事务管理器起效.

     其实大家最感到困惑的是REQUIRED_NEW和NESTED两种不同的传播机制，功能类似，都涉及到了事务嵌套的问题，那两者有何区别呢？该如何正确使用这两种模式呢？

Spring中@Transactional用法深度分析之一

原文：http://blog.csdn.net/blueheart20/article/details/44654007