Spring事务
Spring声明式事务让我们从复杂的事务处理中得到解脱，使我们再也不用去处理这些步骤：获得连接、关闭连接、事务提交和回滚操作。再也不需要在事务相关方法中处理大量的try..catch..finally代码。
Spring中事务的使用虽然已经相对简单的多，但是，还是有很多的使用和配置规则，下面我们开始我们本章重点。
SpringAop基本原理和思想
1、事务保证数据一致性问题，只需要加上@Transactional
2、纯手写SpringAop环绕通知+手动事务就可以声明事务
基于Spring注解方式构建整合JDBC环境
@Repository
public class OrderDao {@Autowired()private JdbcTemplate jdbcTemplate;public void addOrder() {jdbcTemplate.update("insert into order_info values(null,'mayikt','zhangsan','1111')");}
}
@Configuration
@ComponentScan("com.mayikt")
@EnableTransactionManagement//开启事务注解
public class MyConfig { //注入到ioc容器中 beanid =dataSource class=DataSource类的完整路径地址// 配置我们的数据源@Beanpublic DataSource dataSource() {MysqlDataSource mysqlDataSource = new MysqlDataSource();mysqlDataSource.setUser("root");mysqlDataSource.setPassword("root");mysqlDataSource.setURL("jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=UTF-8");mysqlDataSource.setDatabaseName("test");return mysqlDataSource;}/*** 注入JdbcTemplate*/@Beanpublic JdbcTemplate jdbcTemplate() {return new JdbcTemplate(dataSource());}@Beanpublic PlatformTransactionManager platformTransactionManager(){return new DataSourceTransactionManager(dataSource());}
}
@Service
public class OrderServiceImpl implements OrderService {@Autowiredprivate OrderDao orderDao; @Transactional//开启事务public void addOrder() {try {orderDao.addOrder();int i = 1 / 0; // 如果报错的情况下肯定是会插入到数据库中} catch (Exception e) {}}
}
<dependencies><dependency><groupId>org.springframework</groupId><artifactId>spring-context</artifactId><version>5.0.5.RELEASE</version></dependency><!-- mysql 依赖 --><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.46</version></dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-jdbc</artifactId><version>5.0.5.RELEASE</version></dependency> </dependencies>
Spring声明事务底层源码分析
@EnableTransactionManagement//开启事务
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(TransactionManagementConfigurationSelector.class)
public @interface EnableTransactionManagement {
TransactionManagementConfigurationSelector的祖宗是ImportSelector
public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> {@Overrideprotected String[] selectImports(AdviceMode adviceMode) {switch (adviceMode) {case PROXY:return new String[] {AutoProxyRegistrar.class.getName(), ProxyTransactionManagementConfiguration.class.getName()};case ASPECTJ:return new String[] {TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME};default:return null;}}}
public class AutoProxyRegistrar implements ImportBeanDefinitionRegistrar {//向IOC容器中注入Bean对象....@Overridepublic void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {....if (mode != null && proxyTargetClass != null && AdviceMode.class == mode.getClass() &&Boolean.class == proxyTargetClass.getClass()) {candidateFound = true; if (mode == AdviceMode.PROXY) { AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);if ((Boolean) proxyTargetClass) {AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);return;}}}}....
}
public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry) {return registerAutoProxyCreatorIfNecessary(registry, (Object)null);
}
public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, @Nullable Object source) {return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
}
将InfrastructureAdvisorAutoProxyCreator注入到IOC容器中：
InfrastructureAdvisorAutoProxyCreator的类图如下：祖宗是BeanPostProcessor后置处理器，父类是AbstractAutoProxyCreater
回到registerOrEscalateApcAsRequired方法：beanid为：internalAutoProxyCreator，value为：InfrastructureAdvisorAutoProxyCreator对象
private static BeanDefinition registerOrEscalateApcAsRequired(Class<?> cls, BeanDefinitionRegistry registry, @Nullable Object source) {Assert.notNull(registry, "BeanDefinitionRegistry must not be null");if (registry.containsBeanDefinition("org.springframework.aop.config.internalAutoProxyCreator")) {BeanDefinition apcDefinition = registry.getBeanDefinition("org.springframework.aop.config.internalAutoProxyCreator");if (!cls.getName().equals(apcDefinition.getBeanClassName())) {int currentPriority = findPriorityForClass(apcDefinition.getBeanClassName());int requiredPriority = findPriorityForClass(cls);if (currentPriority < requiredPriority) {apcDefinition.setBeanClassName(cls.getName());}}return null;} else {RootBeanDefinition beanDefinition = new RootBeanDefinition(cls);beanDefinition.setSource(source);beanDefinition.getPropertyValues().add("order", -2147483648);beanDefinition.setRole(2); registry.registerBeanDefinition("org.springframework.aop.config.internalAutoProxyCreator", beanDefinition);return beanDefinition;}
}
下面回到ProxyTransactionManagementConfiguration方法
protected String[] selectImports(AdviceMode adviceMode) {switch (adviceMode) {case PROXY:return new String[] {AutoProxyRegistrar.class.getName(), ProxyTransactionManagementConfiguration.class.getName()};case ASPECTJ:return new String[] {TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME};default:return null;}
}
@Configuration
public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration {@Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)@Role(BeanDefinition.ROLE_INFRASTRUCTURE)public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor() {BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();advisor.setTransactionAttributeSource(transactionAttributeSource());advisor.setAdvice(transactionInterceptor());if (this.enableTx != null) {advisor.setOrder(this.enableTx.<Integer>getNumber("order"));}return advisor;}
BeanId:transactionInterceptor;value为：TransactionInterceptor这个对象
打印所有注册的Bean
org.springframework.context.annotation.internalConfigurationAnnotationProcessor
org.springframework.context.annotation.internalAutowiredAnnotationProcessor
org.springframework.context.annotation.internalRequiredAnnotationProcessor
org.springframework.context.annotation.internalCommonAnnotationProcessor
org.springframework.context.event.internalEventListenerProcessor
org.springframework.context.event.internalEventListenerFactory
myConfig
orderDao
orderServiceImpl
org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration
org.springframework.transaction.config.internalTransactionAdvisor
transactionAttributeSource
transactionInterceptor【】【】【】【】这里
org.springframework.transaction.config.internalTransactionalEventListenerFactory
dataSource
jdbcTemplate
platformTransactionManager
org.springframework.aop.config.internalAutoProxyCreator【】【】【】【】这里
加上@EnableTransactionManagement这个注解将 ：TransactionInterceptor，和InternalAutoProxyCreator这两个类注入到IOC容器中
下面重点分析这两个类【transactionInterceptor】，【internalAutoProxyCreator】
从上面类结构可知：InfrastructureAdvisorAutoProxyCreator间接实现了SmartInstantiationAwareBeanPostProcessor，而SmartInstantiationAwareBeanPostProcessor又继承自
InstantiationAwareBeanPostProcessor，也就是说在Spring中，所有的bean实例化时Spring都会保证调用其postProcessAfterInstantiation方法，其实现是在父类AbstractAutoProxyCreater中实现的。
我们一旦把这个类：InfrastructureAdvisorAutoProxyCreator注入到容器中，Bean对象在初始化时，会判断是否需要创建代理类。
进入AbstractAutoProxyCreater的后置处理器:
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) throws BeansException {if (bean != null) { //根据给定的bean的class和name构建出key，beanClassName_beanNameObject cacheKey = this.getCacheKey(bean.getClass(), beanName); //是否是由于避免循环依赖而创建bean的代理if (!this.earlyProxyReferences.contains(cacheKey)) {return this.wrapIfNecessary(bean, beanName, cacheKey);}}return bean;
}
这里实现的主要目的是针对指定的bean进行封装，当然首先要确定是否需要封装，检测及封装的工作都委托给了wrapIfNecessary函数进行。
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) { //如果已经处理过if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {return bean;} else if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {return bean;} else if (!this.isInfrastructureClass(bean.getClass()) && !this.shouldSkip(bean.getClass(), beanName)) {Object[] specificInterceptors = this.getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, (TargetSource)null);if (specificInterceptors != DO_NOT_PROXY) {this.advisedBeans.put(cacheKey, Boolean.TRUE);Object proxy = this.createProxy(bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));//关键点，创建代理，对需要增强的bean创建代理（CGLIBProxy或者JDKProxy）this.proxyTypes.put(cacheKey, proxy.getClass());return proxy;} else {this.advisedBeans.put(cacheKey, Boolean.FALSE);return bean;}} else {this.advisedBeans.put(cacheKey, Boolean.FALSE);return bean;}
}
wrapIfNecessary函数功能实现起来很复杂，但是逻辑上还是相对简单，在wrapIfNecessary函数中主要做了以下工作：
- 找出指定bean对应的增强器【上篇文章详细介绍了，异曲同工】
- 根据找出的增强器创建代理【上篇文章详细介绍了，异曲同工】
下面简单浏览下：
protected Object[] getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName, @Nullable TargetSource targetSource) {List<Advisor> advisors = this.findEligibleAdvisors(beanClass, beanName);return advisors.isEmpty() ? DO_NOT_PROXY : advisors.toArray();
}
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {List<Advisor> candidateAdvisors = this.findCandidateAdvisors();//寻找候选增强器，这里不介绍了List<Advisor> eligibleAdvisors = this.findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);//候选增强器中寻找匹配项，这里分析下....
}
protected List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {....try {var4 = AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
....
}
public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {....while(var3.hasNext()) {Advisor candidate = (Advisor)var3.next(); //首先处理引介增强if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {eligibleAdvisors.add(candidate);}}
....while(var7.hasNext()) {Advisor candidate = (Advisor)var7.next();//对普通bean的处理if (!(candidate instanceof IntroductionAdvisor) && canApply(candidate, clazz, hasIntroductions)) {eligibleAdvisors.add(candidate);}
....}
}
public static boolean canApply(Advisor advisor, Class<?> targetClass, boolean hasIntroductions) {if (advisor instanceof IntroductionAdvisor) {return ((IntroductionAdvisor)advisor).getClassFilter().matches(targetClass);} else if (advisor instanceof PointcutAdvisor) {PointcutAdvisor pca = (PointcutAdvisor)advisor;return canApply(pca.getPointcut(), targetClass, hasIntroductions);} else {return true;}
}
public static boolean canApply(Pointcut pc, Class<?> targetClass, boolean hasIntroductions) {Assert.notNull(pc, "Pointcut must not be null");if (!pc.getClassFilter().matches(targetClass)) {return false;} else { MethodMatcher methodMatcher = pc.getMethodMatcher();....for(int var11 = 0; var11 < var10; ++var11) {Method method = var9[var11];if (introductionAwareMethodMatcher != null && introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions) || methodMatcher.matches(method, targetClass)) {return true;
....}}
}
public boolean matches(Method method, @Nullable Class<?> targetClass) {
....
//自定义标签解析时注入TransactionAttributeSource tas = getTransactionAttributeSource();return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
}
public TransactionAttribute getTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
....else {// We need to work it out.TransactionAttribute txAttr = computeTransactionAttribute(method, targetClass);....
}
protected TransactionAttribute computeTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
.... //method代表接口中的方法，specificMethod代表实现类中的方法 Method specificMethod = AopUtils.getMostSpecificMethod(method, targetClass);// First try is the method in the target class. //查看方法中是否存在事务声明TransactionAttribute txAttr = findTransactionAttribute(specificMethod);if (txAttr != null) {return txAttr;}// Second try is the transaction attribute on the target class.txAttr = findTransactionAttribute(specificMethod.getDeclaringClass());if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {return txAttr;}
//如果存在接口，则到接口中去寻找if (specificMethod != method) {// Fallback is to look at the original method.txAttr = findTransactionAttribute(method);if (txAttr != null) {return txAttr;}// Last fallback is the class of the original method.txAttr = findTransactionAttribute(method.getDeclaringClass());if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {return txAttr;}}return null;
}
对于事务属性的获取规则相信大家都已经很清楚了，如果方法中存在事务属性，则使用方法上的属性，否则使用方法所在类上的属性，如果方法所在类的属性上还是没有搜寻到对应的事务属性，那么再搜寻接口中的方法，再没有的化，
最好尝试搜寻接口的类上面的声明。对于函数computeTransactionAttribute中的逻辑，就是搭建了一个执行框架而已，将搜寻事务属性任务委托给了findTransactionAttribute方法去执行。下面看看这个方法。
protected TransactionAttribute findTransactionAttribute(Method method) {return determineTransactionAttribute(method);
}
protected TransactionAttribute determineTransactionAttribute(AnnotatedElement ae) {for (TransactionAnnotationParser annotationParser : this.annotationParsers) {TransactionAttribute attr = annotationParser.parseTransactionAnnotation(ae);if (attr != null) {return attr;}}return null;
}
public TransactionAttribute parseTransactionAnnotation(AnnotatedElement ae) {AnnotationAttributes attributes = AnnotatedElementUtils.findMergedAnnotationAttributes(ae, Transactional.class, false, false);if (attributes != null) {return parseTransactionAnnotation(attributes);}else {return null;}
}
到这块，我们就看到了我们想看到的获取注解标记的代码。首先会判断当前类是否含有Transactional注解，这是事务属性的基础，当然如果有的化会继续调用parseTransactionAnnotation方法解析详细的属性
protected TransactionAttribute parseTransactionAnnotation(AnnotationAttributes attributes) {RuleBasedTransactionAttribute rbta = new RuleBasedTransactionAttribute(); //解析propagation Propagation propagation = attributes.getEnum("propagation");rbta.setPropagationBehavior(propagation.value()); //解析isolationIsolation isolation = attributes.getEnum("isolation");rbta.setIsolationLevel(isolation.value());rbta.setTimeout(attributes.getNumber("timeout").intValue());rbta.setReadOnly(attributes.getBoolean("readOnly"));rbta.setQualifier(attributes.getString("value"));ArrayList<RollbackRuleAttribute> rollBackRules = new ArrayList<>();Class<?>[] rbf = attributes.getClassArray("rollbackFor");for (Class<?> rbRule : rbf) {RollbackRuleAttribute rule = new RollbackRuleAttribute(rbRule);rollBackRules.add(rule);}String[] rbfc = attributes.getStringArray("rollbackForClassName");for (String rbRule : rbfc) {RollbackRuleAttribute rule = new RollbackRuleAttribute(rbRule);rollBackRules.add(rule);}Class<?>[] nrbf = attributes.getClassArray("noRollbackFor");for (Class<?> rbRule : nrbf) {NoRollbackRuleAttribute rule = new NoRollbackRuleAttribute(rbRule);rollBackRules.add(rule);}String[] nrbfc = attributes.getStringArray("noRollbackForClassName");for (String rbRule : nrbfc) {NoRollbackRuleAttribute rule = new NoRollbackRuleAttribute(rbRule);rollBackRules.add(rule);}rbta.getRollbackRules().addAll(rollBackRules);return rbta;
}
上面方法实现了对对应类或者方法的事务属性解析，你会看到这个类中你所属性的属性。至此，事务功能的初始化工作便结束了
事务增强器
springaop在事务进行调用的时候会走transactionInterceptor进行拦截
执行目标方法，进入invoke()
Spring声明事务源码分析
1.@EnableTransactionManagement开启到我们的事务
2.@Import(TransactionManagementConfigurationSelector.class)
3. AdviceMode mode() default AdviceMode.PROXY;默认使用 PROXY选择器
4.return new String[] {AutoProxyRegistrar.class.getName(), ProxyTransactionManagementConfiguration.class.getName()};
5.加上@EnableTransactionManagement这个注解将 ：TransactionInterceptor，和InternalAutoProxyCreator这两个类注入到IOC容器中
6.进入AbstractAutoProxyCreater的后置处理器的wrapIfNecessary方法针对指定bean进行封装
####6.1.找出指定bean对应的增强器
####6.2.根据找出的增强器创建代理
7.执行目标方法
8.一旦出现异常，尝试异常处理，默认 对（RuntimeException回滚）
9.提交事务前的事务信息清除
10.提交事务。
本文参考
参考书籍：Spring源码深度解析
蚂蚁课堂：http://www.mayikt.com/