springboot如何开启事务@Transactional

客官°小女子只卖身不卖艺 2022-10-16 04:48 114阅读 0赞

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhb21pbmd5YW5n_size_16_color_FFFFFF_t_70]

> 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();
    			}
    		});
    	}

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