Spring事务的传播行为

      Spring的传播行为确定了客户端和被调用端的事务边界，简单来说就是多个具有事务控制的Service的相互调用时所形成的复杂的事务边界控制。Spring定义了7种传播行为，定义的枚举代码如下：

public enum Propagation {

	/**
	 * Support a current transaction, create a new one if none exists.
	 * Analogous to EJB transaction attribute of the same name.
	 * <p>This is the default setting of a transaction annotation.
	 */
	REQUIRED(TransactionDefinition.PROPAGATION_REQUIRED),

	/**
	 * Support a current transaction, execute non-transactionally if none exists.
	 * Analogous to EJB transaction attribute of the same name.
	 * <p>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.
	 */
	SUPPORTS(TransactionDefinition.PROPAGATION_SUPPORTS),

	/**
	 * Support a current transaction, throw an exception if none exists.
	 * 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.
	 * Analogous to the EJB transaction attribute of the same name.
	 * <p>Note: Actual transaction suspension will not work out-of-the-box on
	 * all transaction managers. This in particular applies to JtaTransactionManager,
	 * which requires the {@code javax.transaction.TransactionManager} to be
	 * made available it to it (which is server-specific in standard J2EE).
	 * @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager
	 */
	REQUIRES_NEW(TransactionDefinition.PROPAGATION_REQUIRES_NEW),

	/**
	 * Execute non-transactionally, suspend the current transaction if one exists.
	 * Analogous to EJB transaction attribute of the same name.
	 * <p>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 {@code javax.transaction.TransactionManager} to be
	 * made available it to it (which is server-specific in standard J2EE).
	 * @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager
	 */
	NOT_SUPPORTED(TransactionDefinition.PROPAGATION_NOT_SUPPORTED),

	/**
	 * Execute non-transactionally, throw an exception if a transaction exists.
	 * Analogous to EJB transaction attribute of the same name.
	 */
	NEVER(TransactionDefinition.PROPAGATION_NEVER),

	/**
	 * Execute within a nested transaction if a current transaction exists,
	 * behave like PROPAGATION_REQUIRED else. There is no analogous feature in EJB.
	 * <p>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; }

}

7种传播行为

      

      NESTED与REQUIRES_NEW非常类似，如果调用者不存在一个事务则会开启一个新事务。如果存在一个事务时，内层事务与外层事务就像两个独立的事务一样，一旦内层事务进行了提交后，外层事务不能对其进行回滚，两个事务互不影响，它不是一个真正的嵌套事务。同时需要JTA事务管理器的支持。使用NESTED时，外层事务的回滚可以引起内层事务的回滚，而内层事务的异常并不会导致外层事务的回滚，它是一个真正的嵌套事务。

实例代码

      新建三张数据表，教师信息表、学生信息表和学生评价表：      

CREATE TABLE `Teacher` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT COMMENT '主键',
  `tno` int(11) NOT NULL COMMENT '工号',
  `name` varchar(10) NOT NULL DEFAULT '' COMMENT '姓名',
  `CreateTime` datetime NOT NULL COMMENT '记录插入时间',
  `UpdateTime` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间',
  PRIMARY KEY (`id`),
  UNIQUE KEY `uni_idx_tno` (`tno`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8;     

CREATE TABLE `Student` (
  `ID` int(11) unsigned NOT NULL AUTO_INCREMENT COMMENT '主键',
  `Sno` int(11) NOT NULL COMMENT '学号',
  `Name` varchar(10) NOT NULL DEFAULT '' COMMENT '姓名',
  `Sex` tinyint(2) DEFAULT NULL COMMENT '0:女,1:男',
  `Grade` varchar(10) NOT NULL DEFAULT '' COMMENT '年级',
  `Clazz` tinyint(2) NOT NULL COMMENT '班级',
  `CreateTime` datetime NOT NULL COMMENT '记录插入时间',
  `UpdateTime` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间',
  PRIMARY KEY (`ID`),
  UNIQUE KEY `unix_no` (`Sno`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `Evaluate` (
  `ID` int(11) unsigned NOT NULL AUTO_INCREMENT COMMENT '主键',
  `Sno` int(11) DEFAULT NULL COMMENT '学号',
  `Name` varchar(10) NOT NULL DEFAULT '' COMMENT '姓名',
  `Comment` text NOT NULL COMMENT '评论',
  `Tno` int(11) DEFAULT NULL COMMENT '老师工号',
  `CommentDate` varchar(10) NOT NULL DEFAULT '' COMMENT '评论时间',
  `CreateTime` datetime NOT NULL COMMENT '记录插入时间',
  `UpdateTime` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间',
  PRIMARY KEY (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

REQUIRED和REQUIRED_NEW 

   创建一个方法，老师给学生添加评论的方法，实例代码如下：

 @Transactional(propagation = Propagation.REQUIRED)
    public boolean addEvaluateByTeacher(TeacherDO teacherDO, StudentDO studentDO, EvaluateDO evaluateDO) {
        Integer tno = teacherDao.insert(teacherDO);
        Integer sno = 0;
        try {
            sno = studentDao.insert(studentDO);
        } catch (Exception e) {
        }
        evaluateDO.setSno(sno);
        evaluateDO.setTno(tno);
        return evaluateDao.insert(evaluateDO) > 0 ? true : false;
    }

@Transactional(propagation = Propagation.REQUIRES_NEW,rollbackFor = Exception.class)
    public Integer insert(StudentDO studentDO) {
        if (studentDO == null) {
            LOGGER.error("insert student has error,param is null");
            return 0;
        }
        studentDOMapper.insert(studentDO);
        throw new IllegalArgumentException();
    }

     测试代码如下：

@Test
    public void addEvaluateByTeacher() throws Exception {
        TeacherDO teacherDO = new TeacherDO();
        teacherDO.setTno(5);
        teacherDO.setName("易中天");
        teacherDO.setCreateTime(new Date());
        StudentDO studentDO = new StudentDO();
        studentDO.setName("王晓鹏");
        studentDO.setSno(1111);
        studentDO.setClazz(5);
        studentDO.setSex(1);
        studentDO.setGrade("三年级");
        studentDO.setCreateTime(new Date());

        EvaluateDO evaluateDO = new EvaluateDO();
        evaluateDO.setName("王晓鹏");
        evaluateDO.setComment("好好学习,天天向上");
        evaluateDO.setCreateTime(new Date());
        evaluateDO.setCommentDate("2017-10-01");
        evaluateService.addEvaluateByTeacher(teacherDO, studentDO, evaluateDO);
    }

     执行结果如下：学生信息的insert方法由于使用“REQUIRES_NEW”的事务传播级别，执行时会创建新的事务，该事务和教师添加学生信息以及评论信息的方法addEvaluateByTeacher事务不是同一个事务，当学生信息的insert方法发生异常回滚时会单独回滚，不影响addEvaluateByTeacher。所以，教师信息表和教师评论表可以插入成功，而学生信息表无法插入成功。

MANATORY

     此时我们修改上述的代码，学生信息的insert方法如下：

   @Transactional(propagation = Propagation.MANDATORY)
    public Integer insert(StudentDO studentDO) {
        if (studentDO == null) {
            LOGGER.error("insert student has error,param is null");
            return 0;
        }
        return studentDOMapper.insert(studentDO);
    }

    教师添加学生评论信息代码如下：    

 @Override
    public boolean addEvaluateByTeacher(TeacherDO teacherDO, StudentDO studentDO, EvaluateDO evaluateDO) {
        Integer tno = teacherDao.insert(teacherDO);
        Integer sno = 0;
        sno = studentDao.insert(studentDO);
        evaluateDO.setSno(sno);
        evaluateDO.setTno(tno);
        return evaluateDao.insert(evaluateDO) > 0 ? true : false;
    }

    此时执行单元测试会发生异常，因为事务传播级别MANDATORY的方法必须要求处于一个事务中，如果没有则会抛出异常。数据表中只有教师的信息插入成功，由于执行插入学生信息时抛出了异常，评论信息也会插入失败。执行结果如下：

org.springframework.transaction.IllegalTransactionStateException: No existing transaction found for transaction marked with propagation 'mandatory'

	at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:359)
	at org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:463)
	at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:276)
	at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
	at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207)
	at com.sun.proxy.$Proxy19.insert(Unknown Source)
	at com.jj.tools.service.impl.EvaluateServiceImpl.addEvaluateByTeacher(EvaluateServiceImpl.java:32)
	at com.jj.tools.service.EvaluateServiceImplTest.addEvaluateByTeacher(EvaluateServiceImplTest.java:40)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)

     关于事务的传播行为，暂时就写到这里，其他的传播行为读者可以一一去验证。在实际工作中，读者可以根据自己真实的业务场景去使用，Spring的事务传播行为在开发中占据了很重要的地位。