事务详解
2. 事务管理
2.1 回顾事务
- 什么是事务？
- 在数据库开发中，一组业务逻辑操作，要么全部成功，要么全部失败。
- 事务有什么特定？ACID
- 原子性：整体，原子不可分割的。整个操作被看成一个整体，要么成功，要么失败。
- 一致性：数据，事务操作的前后数据一致。
- 隔离性：并发，两个事务之间并发访问情况。
- 持久性：结果，事务一旦提交，不能回滚。
- 隔离有什么问题？
- 脏读：一个事务读到了另一个事务没有提交的数据。
- 不可重复读：一个事务读到了另一个事务已有提交的数据（update）。
- 幻读：一个事务读到了另一个事务已有提交的数据（insert）。
- 隔离级别有那些？
- 读未提交：存在3个问题（脏读、不可重复读、幻读）
- 读已提交：解决1个问题（脏读），存在2个问题（不可重复读、幻读）
- 可重复读：解决2个问题（脏读、不可重复读）、存在1个问题（幻读）
- 串行化：解决3个问题（脏读、不可重复读、幻读）–单事务
2.2 事务详解
- 研究Spring事务，需要学习事务管理平台管理器：
PlatformTransactionManager- 在平台管理器中，通过
事务的定义获得事务，从而进行事务提交或回滚操作。
- 在平台管理器中，通过
- 事务定义 TransactionDefinition 的详解：
- 传播行为：一个事务调用另一个事务，事务共享问题。
- PROPAGATION_REQUIRED，required：支持当前事务，如果没有事务，创建一个新的。
A 有事务，B使用A的事务。（支持当前事务） A没有事务，B创建新的。（）
- PROPAGATION_SUPPORTS，supports：支持当前事务，如果没有事务，以非事务执行。
A 有事务，B使用A的事务。（支持当前事务） A没有事务，B以非事务执行。
- PROPAGATION_MANDATORY，mandatory：支持当前事务，如果没有事务，抛异常
A 有事务，B使用A的事务。（支持当前事务） A没有事务，B抛异常。
- PROPAGATION_REQUIRES_NEW，requires_new：创建一个新事物，如果当前有事务，将挂起。
A 有事务，B创建新事务，同时挂起A事务。 A 没有事务，B创建新事务。
- PROPAGATION_NOT_SUPPORTED， not_supported：不支持当前事务，以非事务执行，如果有挂起
A 有事务，B以非事务执行，同时挂起A事务。 A 没有事务，B以非事务执行。
- PROPAGATION_NEVER， never：不支持当前事务，如果有抛异常。
A 有事务，B抛异常 A 没有事务，B以非事务执行。
- PROPAGATION_NESTED， nested ：嵌套事务，底层使用
savepoint进行嵌套事务操作。 保存点允许回顾部分事务。
相关源码:
代码语言：javascript复制/*
* Copyright 2002-2015 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.transaction;
import java.sql.Connection;
/**
* Interface that defines Spring-compliant transaction properties.
* Based on the propagation behavior definitions analogous to EJB CMT attributes.
*
* Note that isolation level and timeout settings will not get applied unless
* an actual new transaction gets started. As only {@link #PROPAGATION_REQUIRED},
* {@link #PROPAGATION_REQUIRES_NEW} and {@link #PROPAGATION_NESTED} can cause
* that, it usually doesn't make sense to specify those settings in other cases.
* Furthermore, be aware that not all transaction managers will support those
* advanced features and thus might throw corresponding exceptions when given
* non-default values.
*
* The {@link #isReadOnly() read-only flag} applies to any transaction context,
* whether backed by an actual resource transaction or operating non-transactionally
* at the resource level. In the latter case, the flag will only apply to managed
* resources within the application, such as a Hibernate {@code Session}.
*
* @author Juergen Hoeller
* @since 08.05.2003
* @see PlatformTransactionManager#getTransaction(TransactionDefinition)
* @see org.springframework.transaction.support.DefaultTransactionDefinition
* @see org.springframework.transaction.interceptor.TransactionAttribute
*/
public interface TransactionDefinition {
/**
* Support a current transaction; create a new one if none exists.
* Analogous to the EJB transaction attribute of the same name.
* This is typically the default setting of a transaction definition,
* and typically defines a transaction synchronization scope.
*/
int PROPAGATION_REQUIRED = 0;
/**
* Support a current transaction; execute non-transactionally if none exists.
* Analogous to the EJB transaction attribute of the same name.
* NOTE: For transaction managers with transaction synchronization,
* {@code PROPAGATION_SUPPORTS} is slightly different from no transaction
* at all, as it defines a transaction scope that synchronization might apply to.
* As a consequence, the same resources (a JDBC {@code Connection}, a
* Hibernate {@code Session}, etc) will be shared for the entire specified
* scope. Note that the exact behavior depends on the actual synchronization
* configuration of the transaction manager!
* In general, use {@code PROPAGATION_SUPPORTS} with care! In particular, do
* not rely on {@code PROPAGATION_REQUIRED} or {@code PROPAGATION_REQUIRES_NEW}
* within a {@code PROPAGATION_SUPPORTS} scope (which may lead to
* synchronization conflicts at runtime). If such nesting is unavoidable, make sure
* to configure your transaction manager appropriately (typically switching to
* "synchronization on actual transaction").
* @see org.springframework.transaction.support.AbstractPlatformTransactionManager#setTransactionSynchronization
* @see org.springframework.transaction.support.AbstractPlatformTransactionManager#SYNCHRONIZATION_ON_ACTUAL_TRANSACTION
*/
int PROPAGATION_SUPPORTS = 1;
/**
* Support a current transaction; throw an exception if no current transaction
* exists. Analogous to the EJB transaction attribute of the same name.
* Note that transaction synchronization within a {@code PROPAGATION_MANDATORY}
* scope will always be driven by the surrounding transaction.
*/
int PROPAGATION_MANDATORY = 2;
/**
* Create a new transaction, suspending the current transaction if one exists.
* Analogous to the EJB transaction attribute of the same name.
* NOTE: Actual transaction suspension will not work out-of-the-box
* on all transaction managers. This in particular applies to
* {@link org.springframework.transaction.jta.JtaTransactionManager},
* which requires the {@code javax.transaction.TransactionManager} to be
* made available it to it (which is server-specific in standard Java EE).
* A {@code PROPAGATION_REQUIRES_NEW} scope always defines its own
* transaction synchronizations. Existing synchronizations will be suspended
* and resumed appropriately.
* @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager
*/
int PROPAGATION_REQUIRES_NEW = 3;
/**
* Do not support a current transaction; rather always execute non-transactionally.
* Analogous to the EJB transaction attribute of the same name.
* NOTE: Actual transaction suspension will not work out-of-the-box
* on all transaction managers. This in particular applies to
* {@link org.springframework.transaction.jta.JtaTransactionManager},
* which requires the {@code javax.transaction.TransactionManager} to be
* made available it to it (which is server-specific in standard Java EE).
* Note that transaction synchronization is not available within a
* {@code PROPAGATION_NOT_SUPPORTED} scope. Existing synchronizations
* will be suspended and resumed appropriately.
* @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager
*/
int PROPAGATION_NOT_SUPPORTED = 4;
/**
* Do not support a current transaction; throw an exception if a current transaction
* exists. Analogous to the EJB transaction attribute of the same name.
* Note that transaction synchronization is not available within a
* {@code PROPAGATION_NEVER} scope.
*/
int PROPAGATION_NEVER = 5;
/**
* Execute within a nested transaction if a current transaction exists,
* behave like {@link #PROPAGATION_REQUIRED} else. There is no analogous
* feature in EJB.
* NOTE: Actual creation of a nested transaction will only work on
* specific transaction managers. Out of the box, this only applies to the JDBC
* {@link org.springframework.jdbc.datasource.DataSourceTransactionManager}
* when working on a JDBC 3.0 driver. Some JTA providers might support
* nested transactions as well.
* @see org.springframework.jdbc.datasource.DataSourceTransactionManager
*/
int PROPAGATION_NESTED = 6;
/**
* Use the default isolation level of the underlying datastore.
* All other levels correspond to the JDBC isolation levels.
* @see java.sql.Connection
*/
int ISOLATION_DEFAULT = -1;
/**
* Indicates that dirty reads, non-repeatable reads and phantom reads
* can occur.
* This level allows a row changed by one transaction to be read by another
* transaction before any changes in that row have been committed (a "dirty read").
* If any of the changes are rolled back, the second transaction will have
* retrieved an invalid row.
* @see java.sql.Connection#TRANSACTION_READ_UNCOMMITTED
*/
int ISOLATION_READ_UNCOMMITTED = Connection.TRANSACTION_READ_UNCOMMITTED;
/**
* Indicates that dirty reads are prevented; non-repeatable reads and
* phantom reads can occur.
* This level only prohibits a transaction from reading a row
* with uncommitted changes in it.
* @see java.sql.Connection#TRANSACTION_READ_COMMITTED
*/
int ISOLATION_READ_COMMITTED = Connection.TRANSACTION_READ_COMMITTED;
/**
* Indicates that dirty reads and non-repeatable reads are prevented;
* phantom reads can occur.
* This level prohibits a transaction from reading a row with uncommitted changes
* in it, and it also prohibits the situation where one transaction reads a row,
* a second transaction alters the row, and the first transaction re-reads the row,
* getting different values the second time (a "non-repeatable read").
* @see java.sql.Connection#TRANSACTION_REPEATABLE_READ
*/
int ISOLATION_REPEATABLE_READ = Connection.TRANSACTION_REPEATABLE_READ;
/**
* Indicates that dirty reads, non-repeatable reads and phantom reads
* are prevented.
* This level includes the prohibitions in {@link #ISOLATION_REPEATABLE_READ}
* and further prohibits the situation where one transaction reads all rows that
* satisfy a {@code WHERE} condition, a second transaction inserts a row
* that satisfies that {@code WHERE} condition, and the first transaction
* re-reads for the same condition, retrieving the additional "phantom" row
* in the second read.
* @see java.sql.Connection#TRANSACTION_SERIALIZABLE
*/
int ISOLATION_SERIALIZABLE = Connection.TRANSACTION_SERIALIZABLE;
/**
* Use the default timeout of the underlying transaction system,
* or none if timeouts are not supported.
*/
int TIMEOUT_DEFAULT = -1;
/**
* Return the propagation behavior.
* Must return one of the {@code PROPAGATION_XXX} constants
* defined on {@link TransactionDefinition this interface}.
* @return the propagation behavior
* @see #PROPAGATION_REQUIRED
* @see org.springframework.transaction.support.TransactionSynchronizationManager#isActualTransactionActive()
*/
int getPropagationBehavior();
/**
* Return the isolation level.
* Must return one of the {@code ISOLATION_XXX} constants
* defined on {@link TransactionDefinition this interface}.
* Only makes sense in combination with {@link #PROPAGATION_REQUIRED}
* or {@link #PROPAGATION_REQUIRES_NEW}.
* Note that a transaction manager that does not support custom isolation levels
* will throw an exception when given any other level than {@link #ISOLATION_DEFAULT}.
* @return the isolation level
*/
int getIsolationLevel();
/**
* Return the transaction timeout.
* Must return a number of seconds, or {@link #TIMEOUT_DEFAULT}.
* Only makes sense in combination with {@link #PROPAGATION_REQUIRED}
* or {@link #PROPAGATION_REQUIRES_NEW}.
* Note that a transaction manager that does not support timeouts will throw
* an exception when given any other timeout than {@link #TIMEOUT_DEFAULT}.
* @return the transaction timeout
*/
int getTimeout();
/**
* Return whether to optimize as a read-only transaction.
* The read-only flag applies to any transaction context, whether
* backed by an actual resource transaction
* ({@link #PROPAGATION_REQUIRED}/{@link #PROPAGATION_REQUIRES_NEW}) or
* operating non-transactionally at the resource level
* ({@link #PROPAGATION_SUPPORTS}). In the latter case, the flag will
* only apply to managed resources within the application, such as a
* Hibernate {@code Session}.
<< * This just serves as a hint for the actual transaction subsystem;
* it will not necessarily cause failure of write access attempts.
* A transaction manager which cannot interpret the read-only hint will
* not throw an exception when asked for a read-only transaction.
* @return {@code true} if the transaction is to be optimized as read-only
* @see org.springframework.transaction.support.TransactionSynchronization#beforeCommit(boolean)
* @see org.springframework.transaction.support.TransactionSynchronizationManager#isCurrentTransactionReadOnly()
*/
boolean isReadOnly();
/**
* Return the name of this transaction. Can be {@code null}.
* This will be used as the transaction name to be shown in a
* transaction monitor, if applicable (for example, WebLogic's).
* In case of Spring's declarative transactions, the exposed name will be
* the {@code fully-qualified class name "." method name} (by default).
* @return the name of this transaction
* @see org.springframework.transaction.interceptor.TransactionAspectSupport
* @see org.springframework.transaction.support.TransactionSynchronizationManager#getCurrentTransactionName()
*/
String getName();
}
