摘要：

对SpringBoot有多了解，其实就是看你对Spring Framework有多熟悉~ 比如SpringBoot大量的模块装配的设计模式，其实它属于Spring Framework提供的能力。SpringBoot大行其道的今天，基于XML配置的Spring Framework的使用方式注定已成为过去式。注解驱动应用，面向元数据编程已然成受到越来越多开发者的偏好了，毕竟它的便捷程度、优势都是XML方式不可比拟的。

    @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
            )
          //默认采用cglib代理
            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
      //当PlatformTransactionManager类型的bean存在并且当存在多个bean时指定为Primary的 PlatformTransactionManager存在时,该配置类才进行解析
        @ConditionalOnSingleCandidate(PlatformTransactionManager.class)
        public static class TransactionTemplateConfiguration {
            private final PlatformTransactionManager transactionManager;
    
            public TransactionTemplateConfiguration(PlatformTransactionManager transactionManager) {
                this.transactionManager = transactionManager;
            }
    
         // 由于TransactionAutoConfiguration是在DataSourceTransactionManagerAutoConfiguration之后才被解析处理的,而在DataSourceTransactionManagerAutoConfiguration中配置了transactionManager,因此, TransactionTemplateConfiguration 会被处理.
            @Bean
            @ConditionalOnMissingBean
            public TransactionTemplate transactionTemplate() {
                return new TransactionTemplate(this.transactionManager);
            }
        }
    }

PlatformTransactionManager后续章节会分析

提示：使用@EnableTransactionManagement注解前，请务必保证你已经配置了至少一个PlatformTransactionManager的Bean，否则会报错。（当然你也可以实现TransactionManagementConfigurer来提供一个专属的，只是我们一般都不这么去做~~~）

开启注解驱动

    @Target({ElementType.TYPE})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Import({TransactionManagementConfigurationSelector.class})
    public @interface EnableTransactionManagement {
        boolean proxyTargetClass() default false;
        AdviceMode mode() default Advice