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。
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:
/*
* 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.
*/packageorg.springframework.transaction;importjava.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 {@codeSession}. * *@authorJuergen Hoeller *@since08.05.2003 *@seePlatformTransactionManager#getTransaction(TransactionDefinition) *@seeorg.springframework.transaction.support.DefaultTransactionDefinition *@seeorg.springframework.transaction.interceptor.TransactionAttribute */publicinterfaceTransactionDefinition{/**
* Support a current transaction; create a new one if none exists.
* Analogous to the EJB transaction attribute of the same name.
* <p>This is typically the default setting of a transaction definition,
* and typically defines a transaction synchronization scope.
*/intPROPAGATION_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, * {@codePROPAGATION_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 {@codeConnection}, a * Hibernate {@codeSession}, 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 {@codePROPAGATION_SUPPORTS} with care! In particular, do * not rely on {@codePROPAGATION_REQUIRED} or {@codePROPAGATION_REQUIRES_NEW} * within a {@codePROPAGATION_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"). *@seeorg.springframework.transaction.support.AbstractPlatformTransactionManager#setTransactionSynchronization *@seeorg.springframework.transaction.support.AbstractPlatformTransactionManager#SYNCHRONIZATION_ON_ACTUAL_TRANSACTION */intPROPAGATION_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 {@codePROPAGATION_MANDATORY} * scope will always be driven by the surrounding transaction. */intPROPAGATION_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 * {@linkorg.springframework.transaction.jta.JtaTransactionManager}, * which requires the {@codejavax.transaction.TransactionManager} to be * made available it to it (which is server-specific in standard Java EE). *
A {@codePROPAGATION_REQUIRES_NEW} scope always defines its own * transaction synchronizations. Existing synchronizations will be suspended * and resumed appropriately. *@seeorg.springframework.transaction.jta.JtaTransactionManager#setTransactionManager */intPROPAGATION_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 * {@linkorg.springframework.transaction.jta.JtaTransactionManager}, * which requires the {@codejavax.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 * {@codePROPAGATION_NOT_SUPPORTED} scope. Existing synchronizations * will be suspended and resumed appropriately. *@seeorg.springframework.transaction.jta.JtaTransactionManager#setTransactionManager */intPROPAGATION_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 * {@codePROPAGATION_NEVER} scope. */intPROPAGATION_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 * {@linkorg.springframework.jdbc.datasource.DataSourceTransactionManager} * when working on a JDBC 3.0 driver. Some JTA providers might support * nested transactions as well. *@seeorg.springframework.jdbc.datasource.DataSourceTransactionManager */intPROPAGATION_NESTED =6;/** * Use the default isolation level of the underlying datastore. * All other levels correspond to the JDBC isolation levels. *@seejava.sql.Connection */intISOLATION_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. *@seejava.sql.Connection#TRANSACTION_READ_UNCOMMITTED */intISOLATION_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. *@seejava.sql.Connection#TRANSACTION_READ_COMMITTED */intISOLATION_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"). *@seejava.sql.Connection#TRANSACTION_REPEATABLE_READ */intISOLATION_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 {@codeWHERE} condition, a second transaction inserts a row * that satisfies that {@codeWHERE} condition, and the first transaction * re-reads for the same condition, retrieving the additional "phantom" row * in the second read. *@seejava.sql.Connection#TRANSACTION_SERIALIZABLE */intISOLATION_SERIALIZABLE = Connection.TRANSACTION_SERIALIZABLE;/**
* Use the default timeout of the underlying transaction system,
* or none if timeouts are not supported.
*/intTIMEOUT_DEFAULT = -1;/** * Return the propagation behavior. *
Must return one of the {@codePROPAGATION_XXX} constants * defined on {@linkTransactionDefinition this interface}. *@returnthe propagation behavior *@see#PROPAGATION_REQUIRED *@seeorg.springframework.transaction.support.TransactionSynchronizationManager#isActualTransactionActive() */intgetPropagationBehavior();/** * Return the isolation level. *
Must return one of the {@codeISOLATION_XXX} constants * defined on {@linkTransactionDefinition 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}. *@returnthe isolation level */intgetIsolationLevel();/** * 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}. *@returnthe transaction timeout */intgetTimeout();/** * 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 {@codeSession}. << *
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{@codetrue} if the transaction is to be optimized as read-only *@seeorg.springframework.transaction.support.TransactionSynchronization#beforeCommit(boolean) *@seeorg.springframework.transaction.support.TransactionSynchronizationManager#isCurrentTransactionReadOnly() */booleanisReadOnly();/** * Return the name of this transaction. Can be {@codenull}. *
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 {@codefully-qualified class name + "." + method name} (by default). *@returnthe name of this transaction *@seeorg.springframework.transaction.interceptor.TransactionAspectSupport *@seeorg.springframework.transaction.support.TransactionSynchronizationManager#getCurrentTransactionName() */StringgetName();}
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