springboot如何开启事务@Transactional-蒲公英云

在这里插入图片描述

上图展示了springboot事务管理器实现的一个结构图，直接使用的是JdbcTransactionManager事务管理器，spring的核心接口是PlatformTransactionManager；

一、通过自动化配置类TransactionAutoConfiguration启动spring事务

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

默认使用Cglib动态代理
可以通过spring.aop.proxy-target-class配置修改默认代理方式
通过@EnableTransactionManagement注解开启事务模式

二、EnableTransactionManagement注解将TransactionManagementConfigurationSelector注入容器

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

代理模式默认是JDK动态代理模式
切面的优先级最低
将TransactionManagementConfigurationSelector类注入到容器之中

三、TransactionManagementConfigurationSelector类

public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> { 
    /** * Returns {@link ProxyTransactionManagementConfiguration} or * {@code AspectJ(Jta)TransactionManagementConfiguration} for {@code PROXY} * and {@code ASPECTJ} values of {@link EnableTransactionManagement#mode()}, * respectively. */
    @Override
    protected String[] selectImports(AdviceMode adviceMode) { 
        switch (adviceMode) { 
            case PROXY:
                return new String[] { AutoProxyRegistrar.class.getName(),
                        ProxyTransactionManagementConfiguration.class.getName()};
            case ASPECTJ:
                return new String[] { determineTransactionAspectClass()};
            default:
                return null;
        }
    }
    private String determineTransactionAspectClass() { 
        return (ClassUtils.isPresent("javax.transaction.Transactional", getClass().getClassLoader()) ?
                TransactionManagementConfigUtils.JTA_TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME :
                TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME);
    }
}

默认会将AutoProxyRegistrar和ProxyTransactionManagementConfiguration注入到IOC容器之中；

四、ProxyTransactionManagementConfiguration会实例化TransactionInterceptor切面拦截器，并配置切面及切点

@Bean
    @Role(BeanDefinition.ROLE_INFRASTRUCTURE)
    public TransactionInterceptor transactionInterceptor(TransactionAttributeSource transactionAttributeSource) { 
        TransactionInterceptor interceptor = new TransactionInterceptor();
        interceptor.setTransactionAttributeSource(transactionAttributeSource);
        if (this.txManager != null) { 
            interceptor.setTransactionManager(this.txManager);
        }
        return interceptor;
    }

将TransactionInterceptor切面拦截器注入到IOC容器；

@Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)
    @Role(BeanDefinition.ROLE_INFRASTRUCTURE)
    public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor(
            TransactionAttributeSource transactionAttributeSource, TransactionInterceptor transactionInterceptor) { 
        BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();
        advisor.setTransactionAttributeSource(transactionAttributeSource);
        advisor.setAdvice(transactionInterceptor);
        if (this.enableTx != null) { 
            advisor.setOrder(this.enableTx.<Integer>getNumber("order"));
        }
        return advisor;
    }

将拦截器织入到springboot约定AOP流程中，然后通过@Transactional注解标注的方法就会被织入到约定好的流程之中；

其中TransactionInterceptor拦截器的核心是invoke方法，事物的开启、连接点、织入、事物回滚、事物关闭都是在这个方法搞定;

@Override
    @Nullable
    public Object invoke(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, new CoroutinesInvocationCallback() { 
            @Override
            @Nullable
            public Object proceedWithInvocation() throws Throwable { 
                return invocation.proceed();
            }
            @Override
            public Object getTarget() { 
                return invocation.getThis();
            }
            @Override
            public Object[] getArguments() { 
                return invocation.getArguments();
            }
        });
    }