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Spring Transaction

Dream_it_possible! 人气:0

一、基于xml形式开启Transaction

1. 创建数据库user

/*
 Navicat Premium Data Transfer
 Source Server         : win-local
 Source Server Type    : MySQL
 Source Server Version : 50737
 Source Host           : localhost:3306
 Source Schema         : db0
 Target Server Type    : MySQL
 Target Server Version : 50737
 File Encoding         : 65001
 Date: 24/04/2022 20:27:41
*/
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for user
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user`  (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `age` int(11) NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;
SET FOREIGN_KEY_CHECKS = 1;

2. 创建一个maven 项目

不用Springboot依赖,引入mysql驱动依赖、spring-beans、spring-jdbc、Spring-context依赖

    <dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.46</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-beans</artifactId>
            <version>5.3.18</version>
        </dependency>
        <!-- spring jdbc 依赖spring-tx -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-jdbc</artifactId>
            <version>5.3.18</version>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-dbcp2</artifactId>
            <version>2.7.0</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.3.18</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
        </dependency>
    </dependencies>

3. 通过xml形式配置事务

1) 创建Spring命名空间

首先在resources目录下创建一个spring.xml文件,Spring框架为了声明自己的Xml规范,在<beans>标签里定义了spring 框架指定模块的协议配置, 我们可以通过Index of /schema访问spring框架的所有模块包,各模块包含了不同版本的xsd文件。

点击进入context目录,查看xsd文件:

比如我要通过xml的形式配置一个bean, 需要在beans标签中声明 xmln的值为:

http://www.springframework.org/schema/beans

如果我想用spring的context模块,那么需要声明

xmlns:context="http://www.springframework.org/schema/context"

同时在xsi: schemeLocation里添加context的url和spring-contxt.xsd的url:

http://www.springframework.org/schema/context

https://www.springframework.org/schema/context/spring-context.xsd

例如我创建一个能在xml中使用spring-beans模块,spring-txt模块,spring-context模块的配置如下:

<?xml version="1.0" encoding="UTF-8" ?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="
        http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/tx https://www.springframework.org/schema/tx/spring-tx.xsd
">
</beans>

如果没有在beans标签里声明协议,那么在配置bean时会出现找不到指定标签的问题。

2) 开启事务配置

在spring.xml文件中添加配置事务配置,使用 annotation-driven 属性开启事务启动,

    <tx:annotation-driven transaction-manager="transactionManager" proxy-target-class="true" mode="proxy"/>

proxy-target-class默认为false, mode默认模式为proxy,可不用配置,待会从源码角度分析不同模式的事务开启。

接着配置transactionManager, 指定class="org.springframework.jdbc.datasource.DataSourceTransactionManager"

    <tx:annotation-driven transaction-manager="transactionManager" proxy-target-class="true" mode="proxy"/>
    <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="ds"/>
    </bean>

DataSourceTransactionManager里包含了DataSource属性配置:

因此我们需要接着配置数据源bean 别名为

    <bean id="ds" class="org.apache.commons.dbcp2.BasicDataSource" destroy-method="close">
        <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
        <property name="username" value="root"/>
        <property name="password" value="root"/>
        <property name="url" value="jdbc:mysql://localhost:3306/db0?useSSL=false"/>
        <property name="initialSize" value="5"/>
        <property name="maxIdle" value="2"/>
        <property name="maxTotal" value="100"/>
    </bean>

接着给Service配置一个bean, 引用dataSource数据源。

    <!-- 配置bean,指定数据源-->
    <bean id="userService" class="service.UserService">
        <property name="dataSource" ref="ds"/>
    </bean>

3) 创建UserService类

通过dataSouce bean注入JDBCTemplate, 添加一个update(int id,String name)方法, 类上添加@Transactional(propagation = Propagation.REQUIRED)。

package service;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;
import javax.sql.DataSource;
@Transactional(propagation = Propagation.REQUIRED)
public class UserService {
    private JdbcTemplate jdbcTemplate;
    public void setDataSource(DataSource dataSource) {
        this.jdbcTemplate = new JdbcTemplate(dataSource);
    }
    public String getUserName(int id) {
        return jdbcTemplate.query("select * from db0.user where id= ?", rs -> rs.next() ? rs.getString(2) : "", new Object[]{id});
    }
    public void updateUser(int id, String name) {
        jdbcTemplate.update(" update  user set name =? where id= ?", new Object[]{name, id});
//        throw new RuntimeException("error!");
    }
}

4. 测试事务

使用ClassPathXmlApplicationContext类加载spring.xml文件

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import service.UserService;
public class UserServiceTests {
    @Test
    public void testTransaction() {
        ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
        UserService userService = context.getBean("userService", UserService.class);
        String name = userService.getUserName(1);
        System.out.println("名字:"+name);
        userService.updateUser(1, "bing");
        String updateName = userService.getUserName(1);
        System.out.println("更新后的名字:" + updateName);
    }
}

数据库一条记录:

1) 抛出RuntimeException

update方法里放开//throw new RuntimeException("error!"); 注释,执行后

数据库里的记录没有修改,@Tranasctional注解生效。

2) 注释掉RuntimeException

重新执行后,观察结果

数据库也更新过来了。

前面的篇幅从xml的配置形式解释了Transaction集成过程,为什么要从xml形式入手transaction, 是为了后面阅读Spring-tx源码做准备。

二、事务开启入口TxNamespaceHandler

根据spring.xml文件里配置的tx:annitation-driven 关键字在Spring框架里全局搜索,找到目标类TxNamespaceHandler。位于spring-tx模块中的 org.springframework.transaction.config包下。

/*
 * 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.config;
import org.w3c.dom.Element;
import org.springframework.beans.factory.xml.NamespaceHandlerSupport;
/**
 * {@code NamespaceHandler} allowing for the configuration of
 * declarative transaction management using either XML or using annotations.
 *
 * <p>This namespace handler is the central piece of functionality in the
 * Spring transaction management facilities and offers two approaches
 * to declaratively manage transactions.
 *
 * <p>One approach uses transaction semantics defined in XML using the
 * {@code <tx:advice>} elements, the other uses annotations
 * in combination with the {@code <tx:annotation-driven>} element.
 * Both approached are detailed to great extent in the Spring reference manual.
 *
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @since 2.0
 */
public class TxNamespaceHandler extends NamespaceHandlerSupport {
	static final String TRANSACTION_MANAGER_ATTRIBUTE = "transaction-manager";
	static final String DEFAULT_TRANSACTION_MANAGER_BEAN_NAME = "transactionManager";
	static String getTransactionManagerName(Element element) {
		return (element.hasAttribute(TRANSACTION_MANAGER_ATTRIBUTE) ?
				element.getAttribute(TRANSACTION_MANAGER_ATTRIBUTE) : DEFAULT_TRANSACTION_MANAGER_BEAN_NAME);
	}
	@Override
	public void init() {
		registerBeanDefinitionParser("advice", new TxAdviceBeanDefinitionParser());
		// 注册事务
		registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
		registerBeanDefinitionParser("jta-transaction-manager", new JtaTransactionManagerBeanDefinitionParser());
	}
}

找到了annotation-driven, 这个地方创建了一个AnnotationDrivenBeanDefinitionParser实例。

AnnotationDrivenBeanDefinitionParser

AnnotationDrivenBeanDefinitionParser 类的作用是解析spring.xml里的配置<tx:annotation-driven>标签,并根据配置的mode选择不同的模式取创建Transaction的整个初始化流程,此处也就是整个架Transaction架构的开始地方。

Spring事务注册的模式为动态代理模式,具体实现有2种: aspectj和proxy,可通过配置来选择使用那种形式的事务注册, 如果不配置mode那么使用默认的proxy形式创建,如果我们要使用aspectj模式开启事务,那么就配置mode="aspectj"。

<tx:annotation-driven transaction-manager="transactionManager" mode="aspectj">

我们可以看到Spring事务的开启是默认是以AOP为基础的。

三、AOP驱动事务

AopAutoProxyConfigurer 的configureAutoProxyCreator方法注册了3个Bean, 该3个Bean 是驱动Spring 事务架构的核心支柱,分别是TransactionAttributeSource、TransactionInterceptor、TransactionAttributeSourceAdvisor。

	private static class AopAutoProxyConfigurer {
		public static void configureAutoProxyCreator(Element element, ParserContext parserContext) {
			AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext, element);
			String txAdvisorBeanName = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME;
			if (!parserContext.getRegistry().containsBeanDefinition(txAdvisorBeanName)) {
				Object eleSource = parserContext.extractSource(element);
				// Create the TransactionAttributeSource definition.
				RootBeanDefinition sourceDef = new RootBeanDefinition(
						"org.springframework.transaction.annotation.AnnotationTransactionAttributeSource");
				sourceDef.setSource(eleSource);
				sourceDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
				String sourceName = parserContext.getReaderContext().registerWithGeneratedName(sourceDef);
				// Create the TransactionInterceptor definition.
				RootBeanDefinition interceptorDef = new RootBeanDefinition(TransactionInterceptor.class);
				interceptorDef.setSource(eleSource);
				interceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
				registerTransactionManager(element, interceptorDef);
				interceptorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
				String interceptorName = parserContext.getReaderContext().registerWithGeneratedName(interceptorDef);
				// Create the TransactionAttributeSourceAdvisor definition.
				RootBeanDefinition advisorDef = new RootBeanDefinition(BeanFactoryTransactionAttributeSourceAdvisor.class);
				advisorDef.setSource(eleSource);
				advisorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
				advisorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
				advisorDef.getPropertyValues().add("adviceBeanName", interceptorName);
				if (element.hasAttribute("order")) {
					advisorDef.getPropertyValues().add("order", element.getAttribute("order"));
				}
				// 事务通知器 transaction advisor, 基于AOP实现的advisor
				parserContext.getRegistry().registerBeanDefinition(txAdvisorBeanName, advisorDef);
				CompositeComponentDefinition compositeDef = new CompositeComponentDefinition(element.getTagName(), eleSource);
				compositeDef.addNestedComponent(new BeanComponentDefinition(sourceDef, sourceName));
				compositeDef.addNestedComponent(new BeanComponentDefinition(interceptorDef, interceptorName));
				compositeDef.addNestedComponent(new BeanComponentDefinition(advisorDef, txAdvisorBeanName));
				parserContext.registerComponent(compositeDef);
			}
		}
	}

其中TransactionInterceptor是Spring事务的目标方法的增强,通过代理完成Spring 事务的提交、异常处理和回滚。

TransactionInterceptor

TransactionInterceptor是Spring 事务对目标方法的增强器,说简单点就是一层代理,基于Aop实现,实现了spring-aop的Advice接口,同时实现了IntializingBean和BeanFactoryAware接口,只要有事务的执行,那么目标方法的调用类在invoke()方法会生成一个代理对象,通过invoke()方法对目标调用方法进行增强。

@FunctionalInterface
public interface MethodInterceptor extends Interceptor {
	/**
	 * Implement this method to perform extra treatments before and
	 * after the invocation. Polite implementations would certainly
	 * like to invoke {@link Joinpoint#proceed()}.
	 * @param invocation the method invocation joinpoint
	 * @return the result of the call to {@link Joinpoint#proceed()};
	 * might be intercepted by the interceptor
	 * @throws Throwable if the interceptors or the target object
	 * throws an exception
	 */
	Object invoke(MethodInvocation invocation) throws Throwable;
}

TransactionInterceptor的invoke()实现:

	@Override
	@Nullable
	public Object invoke(final MethodInvocation invocation) throws Throwable {
		// Work out the target class: may be {@code null}.
		// The TransactionAttributeSource should be passed the target class
		// as well as the method, which may be from an interface.
		Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);
		// Adapt to TransactionAspectSupport's invokeWithinTransaction...
		return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);
	}

创建事务

Spring 创建事务的方式有二种: 声明式事务和编程式事务, 我们可以通过分析一种理解核心流程和原理即可。

进入invokeWithinTransaction()方法直接看声明式事务执行过程的源代码:

	if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
			// Standard transaction demarcation with getTransaction and commit/rollback calls.
			// 创建事务
			TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
			Object retVal = null;
			try {
				// This is an around advice: Invoke the next interceptor in the chain.
				// This will normally result in a target object being invoked.
				retVal = invocation.proceedWithInvocation();
			} catch (Throwable ex) {
				// target invocation exception
				// 根据指定异常进行回滚。
				completeTransactionAfterThrowing(txInfo, ex);
				throw ex;
			} finally {
				cleanupTransactionInfo(txInfo);
			}
			// 提交事务
			commitTransactionAfterReturning(txInfo);
			return retVal;
		}

invokeWithinTransaction方法做了哪些事?

1)通过createTransactionIfNecessary方法创建一个事务,相当于此处开启一个事务。

2)invocation.proceedWithInvocation() 执行目标方法调用。

3) 如果出现异常,那么completeTransactionAfterThrowing处理异常。

4) 在finally 清除掉transaction相关的信息,同时在commitTransactionAfterReturning 提交事务。

回滚事务

我们可以从上面的源码中发现通过transactionManager执行回滚操作。

txInfo.getTransactionManager().rollback(txInfo.getTransactionStatus());

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