SpringBoot中的事务处理

作者:xcbeyond
疯狂源自梦想,技术成就辉煌!微信公众号:《程序猿技术大咖》号主,专注后端开发多年,拥有丰富的研发经验,乐于技术输出、分享,现阶段从事微服务架构项目的研发工作,涉及架构设计、技术选型、业务研发等工作。对于Java、微服务、数据库、Docker有深入了解,并有大量的调优经验。












前两章节主要讲解了在SpringBoot中关于对数据的操作,本章节将介绍如何进行事务处理。所有的数据访问技术都离不开事务处理,否则将会造成数据不一致。事务是一系列的动作,一旦其中有一个动作出现错误,必须全部回滚,系统将事务中对数据库的所有已完成的操作全部撤消,滚回到事务开始的状态,避免出现由于数据不一致而导致的接下来一系列的错误。事务的出现是为了确保数据的完整性和一致性,在目前企业级应用开发中,事务管理是必不可少的。

1、SpringBoot事务机制
       事务处理机制都会提供API来开启事务、提交事务来完成数据操作,或者在发生错误的时候回滚数据,避免数据的不完整性、不一致性。

       SpringBoot事务机制实质上就是Spring的事务机制,是采用统一的机制处理来自不同数据访问技术的事务处理,提供了一个接口 PlatformTransactionManager,已经为不同数据访问技术可以进行不同的实现,如下表。
 

涉及到接口关系如下:

接口PlatformTransactionManager源码如下:

/*
 * Copyright 2002-2012 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 org.springframework.lang.Nullable;
 
/**
 * This is the central interface in Spring's transaction infrastructure.
 * Applications can use this directly, but it is not primarily meant as API:
 * Typically, applications will work with either TransactionTemplate or
 * declarative transaction demarcation through AOP.
 *
 * <p>For implementors, it is recommended to derive from the provided
 * {@link org.springframework.transaction.support.AbstractPlatformTransactionManager}
 * class, which pre-implements the defined propagation behavior and takes care
 * of transaction synchronization handling. Subclasses have to implement
 * template methods for specific states of the underlying transaction,
 * for example: begin, suspend, resume, commit.
 *
 * <p>The default implementations of this strategy interface are
 * {@link org.springframework.transaction.jta.JtaTransactionManager} and
 * {@link org.springframework.jdbc.datasource.DataSourceTransactionManager},
 * which can serve as an implementation guide for other transaction strategies.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @since 16.05.2003
 * @see org.springframework.transaction.support.TransactionTemplate
 * @see org.springframework.transaction.interceptor.TransactionInterceptor
 * @see org.springframework.transaction.interceptor.TransactionProxyFactoryBean
 */
public interface PlatformTransactionManager {
 
    /**
     * Return a currently active transaction or create a new one, according to
     * the specified propagation behavior.
     * <p>Note that parameters like isolation level or timeout will only be applied
     * to new transactions, and thus be ignored when participating in active ones.
     * <p>Furthermore, not all transaction definition settings will be supported
     * by every transaction manager: A proper transaction manager implementation
     * should throw an exception when unsupported settings are encountered.
     * <p>An exception to the above rule is the read-only flag, which should be
     * ignored if no explicit read-only mode is supported. Essentially, the
     * read-only flag is just a hint for potential optimization.
     * @param definition TransactionDefinition instance (can be {@code null} for defaults),
     * describing propagation behavior, isolation level, timeout etc.
     * @return transaction status object representing the new or current transaction
     * @throws TransactionException in case of lookup, creation, or system errors
     * @throws IllegalTransactionStateException if the given transaction definition
     * cannot be executed (for example, if a currently active transaction is in
     * conflict with the specified propagation behavior)
     * @see TransactionDefinition#getPropagationBehavior
     * @see TransactionDefinition#getIsolationLevel
     * @see TransactionDefinition#getTimeout
     * @see TransactionDefinition#isReadOnly
     */
    TransactionStatus getTransaction(@Nullable TransactionDefinition definition) throws TransactionException;
 
    /**
     * Commit the given transaction, with regard to its status. If the transaction
     * has been marked rollback-only programmatically, perform a rollback.
     * <p>If the transaction wasn't a new one, omit the commit for proper
     * participation in the surrounding transaction. If a previous transaction
     * has been suspended to be able to create a new one, resume the previous
     * transaction after committing the new one.
     * <p>Note that when the commit call completes, no matter if normally or
     * throwing an exception, the transaction must be fully completed and
     * cleaned up. No rollback call should be expected in such a case.
     * <p>If this method throws an exception other than a TransactionException,
     * then some before-commit error caused the commit attempt to fail. For
     * example, an O/R Mapping tool might have tried to flush changes to the
     * database right before commit, with the resulting DataAccessException
     * causing the transaction to fail. The original exception will be
     * propagated to the caller of this commit method in such a case.
     * @param status object returned by the {@code getTransaction} method
     * @throws UnexpectedRollbackException in case of an unexpected rollback
     * that the transaction coordinator initiated
     * @throws HeuristicCompletionException in case of a transaction failure
     * caused by a heuristic decision on the side of the transaction coordinator
     * @throws TransactionSystemException in case of commit or system errors
     * (typically caused by fundamental resource failures)
     * @throws IllegalTransactionStateException if the given transaction
     * is already completed (that is, committed or rolled back)
     * @see TransactionStatus#setRollbackOnly
     */
    void commit(TransactionStatus status) throws TransactionException;
 
    /**
     * Perform a rollback of the given transaction.
     * <p>If the transaction wasn't a new one, just set it rollback-only for proper
     * participation in the surrounding transaction. If a previous transaction
     * has been suspended to be able to create a new one, resume the previous
     * transaction after rolling back the new one.
     * <p><b>Do not call rollback on a transaction if commit threw an exception.</b>
     * The transaction will already have been completed and cleaned up when commit
     * returns, even in case of a commit exception. Consequently, a rollback call
     * after commit failure will lead to an IllegalTransactionStateException.
     * @param status object returned by the {@code getTransaction} method
     * @throws TransactionSystemException in case of rollback or system errors
     * (typically caused by fundamental resource failures)
     * @throws IllegalTransactionStateException if the given transaction
     * is already completed (that is, committed or rolled back)
     */
    void rollback(TransactionStatus status) throws TransactionException;
 
}
2、声明式事务
         建立在AOP之上的,其本质是对方法前后进行拦截,然后在目标方法开始之前创建或者加入一个事务,在执行完目标方法之后根据执行情况提交或者回滚事务。声明式事务最大的优点就是不需要通过编程的方式管理事务,这样就不需要在业务逻辑代码中掺杂事务管理的代码,只需在配置文件中做相关的事务规则声明(或通过基于@Transactional注解的方式),便可以将事务规则应用到业务逻辑中。

      Spring支持声明式事务,被注解的方法在被调用时,Spring开启一个新的事务,当方法无异常结束后,Spring会提交这个事务。

@Transactional
public void insertUser(User user) {
   //数据库表的操作
    ……
}
注:

(1)@Transactional是来自org.springframework.transaction.annotation包的。

(2)@Transactional不仅可以注解在方法上,也可以注解在类上。当注解在类上时,意味着此类的所有public方法都是开启事务的。如果类级别和方法级别同时使用了@Transactional注解,则使用在类级别的注解会重载方法级别的注解。

以下为注解@Transactional源码:

(为了缩小所占篇数,故去掉注释部分)

package org.springframework.transaction.annotation;
 
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
 
import org.springframework.core.annotation.AliasFor;
import org.springframework.transaction.TransactionDefinition;
 
 
@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Transactional {
 
    @AliasFor("transactionManager")
    String value() default "";
    
    @AliasFor("value")
    String transactionManager() default "";
    
    Propagation propagation() default Propagation.REQUIRED;
 
    Isolation isolation() default Isolation.DEFAULT;
 
    int timeout() default TransactionDefinition.TIMEOUT_DEFAULT;
 
    boolean readOnly() default false;
 
    Class<? extends Throwable>[] rollbackFor() default {};
 
    String[] rollbackForClassName() default {};
    
    Class<? extends Throwable>[] noRollbackFor() default {};
 
    String[] noRollbackForClassName() default {};
}
属性说明如下表:
 

在SpringBoot中,建议采用注解@Transactional进行事务的控制。