我们可以为此添加:

@Transactional(readOnly = true)
public class Banking_CustomerService implements CustomerService {

    public Customer getDetail(String customername) {
        // do something
    }

    // these settings have precedence for this method
    @Transactional(readOnly = false, propagation = Propagation.REQUIRES_NEW)
    public void updateCustomer(Customer customer) {
        // do something
    }
}

你可以这样用:

@Transactional(propagation = Propagation.REQUIRES_NEW)
public EventMessage<ModificaOperativitaRapporto> activate(EventMessage<ModificaOperativitaRapporto> eventMessage) {
//here some transaction related code
}

你也可以用这个东西:

public interface TransactionStatus extends SavepointManager {
    boolean isNewTransaction();
    boolean hasSavepoint();
    void setRollbackOnly();
    boolean isRollbackOnly();
    void flush();
    boolean isCompleted();
}

You almost never want to use Read Uncommited since it's not really ACID compliant. Read Commmited is a good default starting place. Repeatable Read is probably only needed in reporting, rollup or aggregation scenarios. Note that many DBs, postgres included don't actually support Repeatable Read, you have to use Serializable instead. Serializable is useful for things that you know have to happen completely independently of anything else; think of it like synchronized in Java. Serializable goes hand in hand with REQUIRES_NEW propagation.

我对所有运行UPDATE或DELETE查询的函数以及“服务”级函数都使用require。对于只运行select的DAO级函数，我使用SUPPORTS，如果一个已经启动(即从服务函数调用)，它将参与TX。

事务表示数据库的一个工作单元。具有自己的txns(或没有txn)的多个服务中的事务行为称为事务传播。事务隔离定义了当两个事务并发作用于同一个数据库实体时的数据库状态。

TransactionDefinition接口，该接口定义了与spring兼容的事务属性。@Transactional注释描述方法或类上的事务属性。

@Autowired
private TestDAO testDAO;

@Transactional(propagation=TransactionDefinition.PROPAGATION_REQUIRED,isolation=TransactionDefinition.ISOLATION_READ_UNCOMMITTED)
public void someTransactionalMethod(User user) {

  // Interact with testDAO

}

---

传播(复制):用于事务间的关系。(类似于Java线程间通信)

+-------+---------------------------+------------------------------------------------------------------------------------------------------+
| value |        Propagation        |                                             Description                                              |
+-------+---------------------------+------------------------------------------------------------------------------------------------------+
|    -1 | TIMEOUT_DEFAULT           | Use the default timeout of the underlying transaction system, or none if timeouts are not supported. |
|     0 | PROPAGATION_REQUIRED      | Support a current transaction; create a new one if none exists.                                      |
|     1 | PROPAGATION_SUPPORTS      | Support a current transaction; execute non-transactionally if none exists.                           |
|     2 | PROPAGATION_MANDATORY     | Support a current transaction; throw an exception if no current transaction exists.                  |
|     3 | PROPAGATION_REQUIRES_NEW  | Create a new transaction, suspending the current transaction if one exists.                          |
|     4 | PROPAGATION_NOT_SUPPORTED | Do not support a current transaction; rather always execute non-transactionally.                     |
|     5 | PROPAGATION_NEVER         | Do not support a current transaction; throw an exception if a current transaction exists.            |
|     6 | PROPAGATION_NESTED        | Execute within a nested transaction if a current transaction exists.                                 |
+-------+---------------------------+------------------------------------------------------------------------------------------------------+

---

隔离:隔离是数据库事务的ACID(原子性、一致性、隔离性、持久性)属性之一。隔离决定了事务完整性如何对其他用户和系统可见。它用于资源锁定，即并发控制，确保在给定的点上只有一个事务可以访问资源。

锁定感知:隔离级别决定持有锁的持续时间。

+---------------------------+-------------------+-------------+-------------+------------------------+
| Isolation Level Mode      |  Read             |   Insert    |   Update    |       Lock Scope       |
+---------------------------+-------------------+-------------+-------------+------------------------+
| READ_UNCOMMITTED          |  uncommitted data | Allowed     | Allowed     | No Lock                |
| READ_COMMITTED (Default)  |   committed data  | Allowed     | Allowed     | Lock on Committed data |
| REPEATABLE_READ           |   committed data  | Allowed     | Not Allowed | Lock on block of table |
| SERIALIZABLE              |   committed data  | Not Allowed | Not Allowed | Lock on full table     |
+---------------------------+-------------------+-------------+-------------+------------------------+

阅读感悟:出现以下3种主要问题:

脏读:从另一个tx(事务)中读取未提交的数据。 不可重复读取:从另一个tx读取已提交的更新。 幻影读取:从另一个tx读取已提交的insert和/或delete

下面的图表显示了哪个事务隔离级别可以解决哪些并发问题:

+---------------------------+--------------+----------------------+----------------+
| Isolation Level Mode      |  Dirty reads | Non-repeatable reads | Phantoms reads |
+---------------------------+--------------+----------------------+----------------+
| READ_UNCOMMITTED          | X            | X                    | X           |
| READ_COMMITTED (Default)  | solves       | X                    | X           |
| REPEATABLE_READ           | solves       | solves               | X           |
| SERIALIZABLE              | solves       | solves               | solves      |
+---------------------------+--------------+----------------------+----------------+

为例子

其他答案对每个参数都给出了足够的解释;但是，您要求的是一个真实世界的示例，下面是一个阐明不同传播选项的目的的示例:

Suppose you're in charge of implementing a

注册服务

in which a confirmation e-mail is sent to the user. You come up with two service objects, one for

招收

the user and one for

发送

e-mails, which the latter is called inside the first one. For example something like this:

/* Sign Up service */
@Service
@Transactional(Propagation=REQUIRED)
class SignUpService{
 ...
 void SignUp(User user){
    ...
    emailService.sendMail(User);
 }
}

/* E-Mail Service */
@Service
@Transactional(Propagation=REQUIRES_NEW)
class EmailService{
 ...
 void sendMail(User user){
  try{
     ... // Trying to send the e-mail
  }catch( Exception)
 }
}

您可能已经注意到第二个服务的传播类型为REQUIRES_NEW，而且它很可能抛出异常(SMTP服务器宕机、无效电子邮件或其他原因)。你可能不希望整个过程回滚，比如从数据库中删除用户信息或其他东西;因此，在单独的事务中调用第二个服务。

Back to our example, this time you are concerned about the database security, so you define your DAO classes this way:

/* User DAO */
@Transactional(Propagation=MANDATORY)
class UserDAO{
 // some CRUD methods
}

这意味着无论何时创建一个DAO对象，以及因此对DB的潜在访问，我们都需要确保调用是从我们的一个服务内部发出的，这意味着应该存在一个活动事务;否则会出现异常。因此，传播类型为MANDATORY。

我们可以为此添加:

@Transactional(readOnly = true)
public class Banking_CustomerService implements CustomerService {

    public Customer getDetail(String customername) {
        // do something
    }

    // these settings have precedence for this method
    @Transactional(readOnly = false, propagation = Propagation.REQUIRES_NEW)
    public void updateCustomer(Customer customer) {
        // do something
    }
}