springboot使用事务原理

在springboot项目中，无需使用@EnableTransactionManagement注解，可以直接在业务方法上添加@Transactional注解,即可；但是如果是单纯的springmvc项目的话，就需要在配置类上添加@EnableTransactionManagement注解来开启全局事务

其实原因也很简单，就是因为springboot项目在启动的时候，帮我们自动添加了@EnableTransactionManagement注解；

在spring-boot-autoconfigure-2.2.2.RELEASE.jar这个jar包中，定义了要自动注入的bean

org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration

但是这个bean的注入，有一个前提条件，必须在DataSourceTransactionManagerAutoConfiguration这个bean注入之后，才会注入TransactionAutoConfiguration

在TransactionAutoConfiguration这个bean中，声明了一个静态内部类：EnableTransactionManagementConfiguration
在其类中，声明了开启事务注解的注释

@Configuration(
        proxyBeanMethods = false
)
@ConditionalOnBean({
    
    TransactionManager.class})
@ConditionalOnMissingBean({
    
    AbstractTransactionManagementConfiguration.class})
public static class EnableTransactionManagementConfiguration {
    
    
	public EnableTransactionManagementConfiguration() {
    
    
	}

	@Configuration(
		proxyBeanMethods = false
	)
	@EnableTransactionManagement(
		proxyTargetClass = true
	)
	@ConditionalOnProperty(
		prefix = "spring.aop",
		name = {
    
    "proxy-target-class"},
		havingValue = "true",
		matchIfMissing = true
	)
	public static class CglibAutoProxyConfiguration {
    
    
		public CglibAutoProxyConfiguration() {
    
    
		}
	}

	@Configuration(
		proxyBeanMethods = false
	)
	@EnableTransactionManagement(
		proxyTargetClass = false
	)
	@ConditionalOnProperty(
		prefix = "spring.aop",
		name = {
    
    "proxy-target-class"},
		havingValue = "false",
		matchIfMissing = false
	)
	public static class JdkDynamicAutoProxyConfiguration {
    
    
		public JdkDynamicAutoProxyConfiguration() {
    
    
		}
	}
}