Spring相关面试题:谈一谈你对事务的理解?-CFANZ编程社区

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：

Spring相关面试题:谈一谈你对事务的理解?_sql

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.
 */

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.
 *
 * <p>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.
 *
 * <p>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.
   * <p>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.
   * <p><b>NOTE:</b> 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!
   * <p>In general, use {@code PROPAGATION_SUPPORTS} with care! In particular, do
   * not rely on {@code PROPAGATION_REQUIRED} or {@code PROPAGATION_REQUIRES_NEW}
   * <i>within</i> 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.
   * <p>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.
   * <p><b>NOTE:</b> 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).
   * <p>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.
   * <p><b>NOTE:</b> 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).
   * <p>Note that transaction synchronization is <i>not</i> 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.
   * <p>Note that transaction synchronization is <i>not</i> 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.
   * <p><b>NOTE:</b> 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.
   * <p>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.
   * <p>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.
   * <p>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.
   * <p>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.
   * <p>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.
   * <p>Must return one of the {@code ISOLATION_XXX} constants
   * defined on {@link TransactionDefinition this interface}.
   * <p>Only makes sense in combination with {@link #PROPAGATION_REQUIRED}
   * or {@link #PROPAGATION_REQUIRES_NEW}.
   * <p>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.
   * <p>Must return a number of seconds, or {@link #TIMEOUT_DEFAULT}.
   * <p>Only makes sense in combination with {@link #PROPAGATION_REQUIRED}
   * or {@link #PROPAGATION_REQUIRES_NEW}.
   * <p>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.
   * <p>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}.
   <<  * <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.
   * @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}.
   * <p>This will be used as the transaction name to be shown in a
   * transaction monitor, if applicable (for example, WebLogic's).
   * <p>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();

}