一、声明式事务
1、引入spring-tx依赖
<dependency>
<groupId>org.mybatis.spring.boot</groupId>
<artifactId>mybatis-spring-boot-starter</artifactId>
<version>1.2.0</version>
</dependency>
和事务相关的jar包spring-tx-5.0.2.RELEASE.jar，spring框架为我们提供了一组事务控制的接口。这组接口是在spring-tx-5.0.2.RELEASE.jar 中。
spring-data.redis中含有spring-tx依赖
mybatis-spring-boot-starter中也有spring-txjar包
2、在启动类中添加@EnableTransactionManagement注解开启事务（这步可以省略）
注意：springboot项目中，启动类不添加@EnableTransactionManagement注解也可以开启事务。
3、在Service实现类中添加@Transactional注解
springboot为何不使用@EnableTransactionManagement就能使用事务？
有些注解如果每个人配置时都是一样的，在springboot中，我们可以将这些注解设置为默认。
自动配置原理解析：
1、按住Ctrl点击查看启动类MySpringBootApplication上的注解@SpringBootApplication，注解@SpringBootApplication的源码如下：
@EnableAutoConfiguration：开启SpringBoot自动配置功能
2、按住Ctrl点击查看注解@EnableAutoConfiguration
其中，@Import(AutoConfigurationImportSelector.class) 导入了AutoConfigurationImportSelector类，
3、按住Ctrl点击查看AutoConfigurationImportSelector源码
public String[] selectImports(AnnotationMetadata annotationMetadata) { if (!this.isEnabled(annotationMetadata)) { return NO_IMPORTS; } else { AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader); AutoConfigurationImportSelector.AutoConfigurationEntry autoConfigurationEntry = this.getAutoConfigurationEntry(autoConfigurationMetadata, annotationMetadata); return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations()); } }
找到自动获得的Entry，进入其源代码：
protected AutoConfigurationImportSelector.AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata, AnnotationMetadata annotationMetadata) { if (!this.isEnabled(annotationMetadata)) { return EMPTY_ENTRY; } else { AnnotationAttributes attributes = this.getAttributes(annotationMetadata); List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes); configurations = this.removeDuplicates(configurations); Set<String> exclusions = this.getExclusions(annotationMetadata, attributes); this.checkExcludedClasses(configurations, exclusions); configurations.removeAll(exclusions); configurations = this.filter(configurations, autoConfigurationMetadata); this.fireAutoConfigurationImportEvents(configurations, exclusions); return new AutoConfigurationImportSelector.AutoConfigurationEntry(configurations, exclusions); } }
protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) { List<String> configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader()); Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you are using a custom packaging, make sure that file is correct."); return configurations; }
其中，SpringFactoriesLoader.loadFactoryNames 方法的作用就是从META-INF/spring.factories文件中读取指定类对应的类名称列表
# Auto Configure org.springframework.boot.autoconfigure.EnableAutoConfiguration=\ org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\ org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\ org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\ org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\ org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\ org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\ org.springframework.boot.autoconfigure.cloud.CloudServiceConnectorsAutoConfiguration,\ org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\ org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\ org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\ org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\ org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\ org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\ org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\ org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\ org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\ org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\ org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration,\ org.springframework.boot.autoconfigure.elasticsearch.rest.RestClientAutoConfiguration,\ org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\ org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\ org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\ org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\ org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\ org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\ org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\ org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration,\ org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\ org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\ org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\ org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\ org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\ org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\ org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\ org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\ org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\ org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\ org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\ org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\ org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\ org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\ org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\ org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\ org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\ org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\ org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\ org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\ org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\ org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\ org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\ org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\ org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\ org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\ org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\ org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\ org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\ org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\ org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\ org.springframework.boot.autoconfigure.reactor.core.ReactorCoreAutoConfiguration,\ org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\ org.springframework.boot.autoconfigure.security.servlet.SecurityRequestMatcherProviderAutoConfiguration,\ org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\ org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\ org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\ org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\ org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\ org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\ org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAuth2ClientAutoConfiguration,\ org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,\ org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,\ org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,\ org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\ org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\ org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,\ org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\ org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\ org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\ org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\ org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,\ org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\ org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\ org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\ org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\ org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\ org.springframework.boot.autoconfigure.web.reactive.function.client.ClientHttpConnectorAutoConfiguration,\ org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\ org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\ org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\ org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\ org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\ org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\ org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\ org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\ org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\ org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\ org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration,\ org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration
上面配置文件存在大量的以Configuration为结尾的类名称，这些类就是存有自动配置信息的类，而SpringApplication在获取这些类名后再加载
点击TransactionAutoConfiguration查看源代码：
@Configuration @ConditionalOnClass({PlatformTransactionManager.class}) @AutoConfigureAfter({JtaAutoConfiguration.class, HibernateJpaAutoConfiguration.class, DataSourceTransactionManagerAutoConfiguration.class, Neo4jDataAutoConfiguration.class}) @EnableConfigurationProperties({TransactionProperties.class}) public class TransactionAutoConfiguration { public TransactionAutoConfiguration() { } @Bean @ConditionalOnMissingBean public TransactionManagerCustomizers platformTransactionManagerCustomizers(ObjectProvider<PlatformTransactionManagerCustomizer<?>> customizers) { return new TransactionManagerCustomizers((Collection)customizers.orderedStream().collect(Collectors.toList())); } @Configuration @ConditionalOnBean({PlatformTransactionManager.class}) @ConditionalOnMissingBean({AbstractTransactionManagementConfiguration.class}) public static class EnableTransactionManagementConfiguration { public EnableTransactionManagementConfiguration() { } @Configuration @EnableTransactionManagement( proxyTargetClass = true ) @ConditionalOnProperty( prefix = "spring.aop", name = {"proxy-target-class"}, havingValue = "true", matchIfMissing = true ) public static class CglibAutoProxyConfiguration { public CglibAutoProxyConfiguration() { } } @Configuration @EnableTransactionManagement( proxyTargetClass = false ) @ConditionalOnProperty( prefix = "spring.aop", name = {"proxy-target-class"}, havingValue = "false", matchIfMissing = false ) public static class JdkDynamicAutoProxyConfiguration { public JdkDynamicAutoProxyConfiguration() { } } } @Configuration @ConditionalOnSingleCandidate(PlatformTransactionManager.class) public static class TransactionTemplateConfiguration { private final PlatformTransactionManager transactionManager; public TransactionTemplateConfiguration(PlatformTransactionManager transactionManager) { this.transactionManager = transactionManager; } @Bean @ConditionalOnMissingBean public TransactionTemplate transactionTemplate() { return new TransactionTemplate(this.transactionManager); } } }
这个开启事务的管理其实与我们今天所说的@EnableTransactionManagement源代码说的是一样的，所以此注解可加与不可加是没有问题的。
二、编程式事务
使用TransactionTemplate 不需要显式地开始事务，甚至不需要显式地提交事务。这些步骤都由模板完成。但出现异常时，应通过TransactionStatus 的setRollbackOnly 显式回滚事务。TransactionTemplate是线程安全的。
TransactionTemplate 的execute 方法接收一个TransactionCallback 实例。Callback 也是Spring 的经典设计，用于简化用户操作， TransactionCallback 包含如下方法。
• Object dolnTransaction(TransactionStatus status) 。
该方法的方法体就是事务的执行体。
如果事务的执行体没有返回值，则可以使用TransactionCallbackWithoutResultl类的实例。这是个抽象类，不能直接实例化，只能用于创建匿名内部类。它也是TransactionCallback 接口的子接口，该抽象类包含一个抽象方法:
• void dolnTransactionWithoutResult(TransactionStatus status)该方法与dolnTransaction 的效果非常相似，区别在于该方法没有返回值，即事务执行体无须返回值。
（1）、没有返回值时
transactionTemplate.execute(new TransactionCallbackWithoutResult() { @SneakyThrows protected void doInTransactionWithoutResult(TransactionStatus status) { try { userService.save(userEntity); ss(); } catch (Exception e) { status.setRollbackOnly(); System.out.println("xxxx"); throw e; } } });
（2）、有返回值时
transactionTemplate.execute(new TransactionCallback<Object>() { @Override public Object doInTransaction(TransactionStatus status) { return userService.save(userEntity); } })
