Spring 事务理解
先看代码,再debug看看
主要是基于Spring AOP
一、事务的基本原理
Spring事务的本质其实就是数据库对事务的支持,没有数据库的事务支持,spring是无法提供事务功能的。对于纯JDBC操作数据库,想要用到事务,可以按照以下步骤进行:
获取连接 Connection con = DriverManager.getConnection()
开启事务con.setAutoCommit(true/false);
执行CRUD
提交事务/回滚事务 con.commit() / con.rollback();
关闭连接 conn.close();
使用Spring的事务管理功能后,我们可以不再写步骤 2 和 4 的代码,而是由Spirng 自动完成。 那么Spring是如何在我们书写的 CRUD 之前和之后开启事务和关闭事务的呢?解决这个问题,也就可以从整体上理解Spring的事务管理实现原理了。下面简单地介绍下,注解方式为例子
配置文件开启注解驱动,在相关的类和方法上通过注解@Transactional标识。
spring 在启动的时候会去解析生成相关的bean,这时候会查看拥有相关注解的类和方法,并且为这些类和方法生成代理,并根据@Transaction的相关参数进行相关配置注入,这样就在代理中为我们把相关的事务处理掉了(开启正常提交事务,异常回滚事务)。
真正的数据库层的事务提交和回滚是通过binlog或者redo log实现的。
二、Spring 事务的传播属性
所谓spring事务的传播属性,就是定义在存在多个事务同时存在的时候,spring应该如何处理这些事务的行为。这些属性在TransactionDefinition中定义,具体常量的解释见下表:
常量名称 常量解释
PROPAGATION_REQUIRED 支持当前事务,如果当前没有事务,就新建一个事务。这是最常见的选择,也是 Spring 默认的事务的传播。
PROPAGATION_REQUIRES_NEW 新建事务,如果当前存在事务,把当前事务挂起。新建的事务将和被挂起的事务没有任何关系,是两个独立的事务,外层事务失败回滚之后,不能回滚内层事务执行的结果,内层事务失败抛出异常,外层事务捕获,也可以不处理回滚操作
PROPAGATION_SUPPORTS 支持当前事务,如果当前没有事务,就以非事务方式执行。
PROPAGATION_MANDATORY 支持当前事务,如果当前没有事务,就抛出异常。
PROPAGATION_NOT_SUPPORTED 以非事务方式执行操作,如果当前存在事务,就把当前事务挂起。
PROPAGATION_NEVER 以非事务方式执行,如果当前存在事务,则抛出异常。
PROPAGATION_NESTED
如果一个活动的事务存在,则运行在一个嵌套的事务中。如果没有活动事务,则按REQUIRED属性执行。它使用了一个单独的事务,这个事务拥有多个可以回滚的保存点。内部事务的回滚不会对外部事务造成影响。它只对DataSourceTransactionManager事务管理器起效。
三、数据库隔离级别
隔离级别 隔离级别的值 导致的问题
Read-Uncommitted 0 导致脏读
Read-Committed 1 避免脏读,允许不可重复读和幻读
Repeatable-Read 2 避免脏读,不可重复读,允许幻读
Serializable 3 串行化读,事务只能一个一个执行,避免了脏读、不可重复读、幻读。执行效率慢,使用时慎重
脏读:一事务对数据进行了增删改,但未提交,另一事务可以读取到未提交的数据。如果第一个事务这时候回滚了,那么第二个事务就读到了脏数据。
不可重复读:一个事务中发生了两次读操作,第一次读操作和第二次操作之间,另外一个事务对数据进行了修改,这时候两次读取的数据是不一致的。
幻读:第一个事务对一定范围的数据进行批量修改,第二个事务在这个范围增加一条数据,这时候第一个事务就会丢失对新增数据的修改。
总结:
隔离级别越高,越能保证数据的完整性和一致性,但是对并发性能的影响也越大。
大多数的数据库默认隔离级别为 Read Commited,比如 SqlServer、Oracle
少数数据库默认隔离级别为:Repeatable Read 比如: MySQL InnoDB
四、Spring中的隔离级别
常量 解释
ISOLATION_DEFAULT 这是个 PlatfromTransactionManager 默认的隔离级别,使用数据库默认的事务隔离级别。另外四个与 JDBC 的隔离级别相对应。
ISOLATION_READ_UNCOMMITTED 这是事务最低的隔离级别,它充许另外一个事务可以看到这个事务未提交的数据。这种隔离级别会产生脏读,不可重复读和幻像读。
ISOLATION_READ_COMMITTED 保证一个事务修改的数据提交后才能被另外一个事务读取。另外一个事务不能读取该事务未提交的数据。
ISOLATION_REPEATABLE_READ 这种事务隔离级别可以防止脏读,不可重复读。但是可能出现幻像读。
ISOLATION_SERIALIZABLE 这是花费最高代价但是最可靠的事务隔离级别。事务被处理为顺序执行。
五、事务的嵌套
通过上面的理论知识的铺垫,我们大致知道了数据库事务和spring事务的一些属性和特点,接下来我们通过分析一些嵌套事务的场景,来深入理解spring事务传播的机制。
假设外层事务 Service A 的 Method A() 调用 内层Service B 的 Method B()
PROPAGATION_REQUIRED(spring 默认)
如果ServiceB.methodB() 的事务级别定义为 PROPAGATION_REQUIRED,那么执行 ServiceA.methodA() 的时候spring已经起了事务,这时调用 ServiceB.methodB(),ServiceB.methodB() 看到自己已经运行在 ServiceA.methodA() 的事务内部,就不再起新的事务。
假如 ServiceB.methodB() 运行的时候发现自己没有在事务中,他就会为自己分配一个事务。
这样,在 ServiceA.methodA() 或者在 ServiceB.methodB() 内的任何地方出现异常,事务都会被回滚。
PROPAGATION_REQUIRES_NEW
比如我们设计 ServiceA.methodA() 的事务级别为 PROPAGATION_REQUIRED,ServiceB.methodB() 的事务级别为 PROPAGATION_REQUIRES_NEW。
那么当执行到 ServiceB.methodB() 的时候,ServiceA.methodA() 所在的事务就会挂起,ServiceB.methodB() 会起一个新的事务,等待 ServiceB.methodB() 的事务完成以后,它才继续执行。
他与 PROPAGATION_REQUIRED 的事务区别在于事务的回滚程度了。因为 ServiceB.methodB() 是新起一个事务,那么就是存在两个不同的事务。如果 ServiceB.methodB() 已经提交,那么 ServiceA.methodA() 失败回滚,ServiceB.methodB() 是不会回滚的。如果 ServiceB.methodB() 失败回滚,如果他抛出的异常被 ServiceA.methodA() 捕获,ServiceA.methodA() 事务仍然可能提交(主要看B抛出的异常是不是A会回滚的异常)。
PROPAGATION_SUPPORTS
假设ServiceB.methodB() 的事务级别为 PROPAGATION_SUPPORTS,那么当执行到ServiceB.methodB()时,如果发现ServiceA.methodA()已经开启了一个事务,则加入当前的事务,如果发现ServiceA.methodA()没有开启事务,则自己也不开启事务。这种时候,内部方法的事务性完全依赖于最外层的事务。
PROPAGATION_NESTED
现在的情况就变得比较复杂了, ServiceB.methodB() 的事务属性被配置为 PROPAGATION_NESTED, 此时两者之间又将如何协作呢? ServiceB#methodB 如果 rollback, 那么内部事务(即 ServiceB#methodB) 将回滚到它执行前的 SavePoint 而外部事务(即 ServiceA#methodA) 可以有以下两种处理方式:
a、捕获异常,执行异常分支逻辑
void methodA() {
try {
ServiceB.methodB();
} catch (SomeException) {
// 执行其他业务, 如 ServiceC.methodC();
}
}
这种方式也是嵌套事务最有价值的地方, 它起到了分支执行的效果, 如果 ServiceB.methodB 失败, 那么执行 ServiceC.methodC(), 而 ServiceB.methodB 已经回滚到它执行之前的 SavePoint, 所以不会产生脏数据(相当于此方法从未执行过), 这种特性可以用在某些特殊的业务中, 而 PROPAGATION_REQUIRED 和 PROPAGATION_REQUIRES_NEW 都没有办法做到这一点。
b、 外部事务回滚/提交 代码不做任何修改, 那么如果内部事务(ServiceB#methodB) rollback, 那么首先 ServiceB.methodB 回滚到它执行之前的 SavePoint(在任何情况下都会如此), 外部事务(即 ServiceA#methodA) 将根据具体的配置决定自己是 commit 还是 rollback
另外三种事务传播属性基本用不到,在此不做分析。
六、总结
对于项目中需要使用到事务的地方,我建议开发者还是使用spring的TransactionCallback接口来实现事务,不要盲目使用spring事务注解,如果一定要使用注解,那么一定要对spring事务的传播机制和隔离级别有个详细的了解,否则很可能发生意想不到的效果。
spring.xml中事务的配置
<bean id="genOneTransactionManager"
class="org.springframework.jdbc.datasource.DataSourceTransactionManager"
abstract="false" lazy-init="default" autowire="default">
<property name="dataSource">
<ref bean="genOneDataSource" />
</property>
</bean>
<tx:annotation-driven transaction-manager="genOneTransactionManager" />
NameSpace 解析tx标签
public class TxNamespaceHandler extends NamespaceHandlerSupport {
static final String TRANSACTION_MANAGER_ATTRIBUTE = "transaction-manager";
static final String DEFAULT_TRANSACTION_MANAGER_BEAN_NAME = "transactionManager";
static String getTransactionManagerName(Element element) {
return (element.hasAttribute(TRANSACTION_MANAGER_ATTRIBUTE) ?
element.getAttribute(TRANSACTION_MANAGER_ATTRIBUTE) : DEFAULT_TRANSACTION_MANAGER_BEAN_NAME);
}
@Override
public void init() {
registerBeanDefinitionParser("advice", new TxAdviceBeanDefinitionParser());
registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
registerBeanDefinitionParser("jta-transaction-manager", new JtaTransactionManagerBeanDefinitionParser());
}
}
数据库事务的配置 采用注解方式
@Transactional(value = "genOneTransactionManager", propagation = Propagation.REQUIRED, rollbackFor = Exception.class)
public void deleteCostVO(String costIntervalSystemNo, String costInfoSystemNo) throws Exception {
String sqlForInterval = "DELETE FROM CB_CostInterval WHERE SystemNo = ?";
String sqlForBasicCost = "DELETE FROM CB_BasicCost WHERE CostIntervalSystemNo = ?";
String sqlForDiscountCost = "DELETE FROM CB_BasicCost WHERE CostIntervalSystemNo = ?";
String sqlForCostInfo = "DELETE FROM CB_CostInfo WHERE SystemNo = ?";
String sqlForItemCostRel = "DELETE FROM CB_ChannelProItemCostRel WHERE CostInfoSystemNo = ?";
smartDAO.update(FinanceModuleConstants.FINANCE_NAME, sqlForInterval, new Object[] { costIntervalSystemNo });
smartDAO.update(FinanceModuleConstants.FINANCE_NAME, sqlForBasicCost, new Object[] { costIntervalSystemNo });
smartDAO.update(FinanceModuleConstants.FINANCE_NAME, sqlForDiscountCost, new Object[] { costIntervalSystemNo });
List<CbCostInterval> intervals = cbCostIntervalQuery.getListByCostInfoSystemNo(costInfoSystemNo);
if (intervals.isEmpty()) {
smartDAO.update(FinanceModuleConstants.FINANCE_NAME, sqlForCostInfo, new Object[] { costInfoSystemNo });
smartDAO.update(FinanceModuleConstants.FINANCE_NAME, sqlForItemCostRel, new Object[] { costInfoSystemNo });
}
}
关注AnnotationDrivenBeanDefinitionParser 类 的parse方法
@Override
public BeanDefinition parse(Element element, ParserContext parserContext) {
registerTransactionalEventListenerFactory(parserContext);
String mode = element.getAttribute("mode");
if ("aspectj".equals(mode)) {
// mode="aspectj"
registerTransactionAspect(element, parserContext);
}
else {
// mode="proxy"
AopAutoProxyConfigurer.configureAutoProxyCreator(element, parserContext);
}
return null;
}
private static class AopAutoProxyConfigurer {
public static void configureAutoProxyCreator(Element element, ParserContext parserContext) {
AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext, element);
String txAdvisorBeanName = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME;
if (!parserContext.getRegistry().containsBeanDefinition(txAdvisorBeanName)) {
Object eleSource = parserContext.extractSource(element);
// Create the TransactionAttributeSource definition.
//创建 TransactionAttributeSource 的bean
RootBeanDefinition sourceDef = new RootBeanDefinition(
"org.springframework.transaction.annotation.AnnotationTransactionAttributeSource");
sourceDef.setSource(eleSource);
sourceDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
//注册bean 并使用Springbean中的定义规则生成beanName
String sourceName = parserContext.getReaderContext().registerWithGeneratedName(sourceDef);
// Create the TransactionInterceptor definition.
// 创建TransactionInterceptor 的bean
RootBeanDefinition interceptorDef = new RootBeanDefinition(TransactionInterceptor.class);
interceptorDef.setSource(eleSource);
interceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
// 将 interceptorName的bean注入到advisorDef的advicebean中
registerTransactionManager(element, interceptorDef);
interceptorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
// 注册 bean 并使用spring中的规则生成beanName
String interceptorName = parserContext.getReaderContext().registerWithGeneratedName(interceptorDef);
// Create the TransactionAttributeSourceAdvisor definition.
RootBeanDefinition advisorDef = new RootBeanDefinition(BeanFactoryTransactionAttributeSourceAdvisor.class);
advisorDef.setSource(eleSource);
advisorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
advisorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
advisorDef.getPropertyValues().add("adviceBeanName", interceptorName);
if (element.hasAttribute("order")) {
advisorDef.getPropertyValues().add("order", element.getAttribute("order"));
}
parserContext.getRegistry().registerBeanDefinition(txAdvisorBeanName, advisorDef);
// 构建CompositeComponentDefinition
CompositeComponentDefinition compositeDef = new CompositeComponentDefinition(element.getTagName(), eleSource);
compositeDef.addNestedComponent(new BeanComponentDefinition(sourceDef, sourceName));
compositeDef.addNestedComponent(new BeanComponentDefinition(interceptorDef, interceptorName));
compositeDef.addNestedComponent(new BeanComponentDefinition(advisorDef, txAdvisorBeanName));
parserContext.registerComponent(compositeDef);
}
}
}
configureAutoProxyCreator 方法注册了三个bean ,interceptorDef、advisorDef、compositeDef
这三个bean支持了整个事务的功能
在看一个很重要的一行, 事务上面的注解配置是怎么加载进来的呢?
看这一行
AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext, element);
点进去,看
public abstract class AopNamespaceUtils {
/**
* The {@code proxy-target-class} attribute as found on AOP-related XML tags.
*/
public static final String PROXY_TARGET_CLASS_ATTRIBUTE = "proxy-target-class";
/**
* The {@code expose-proxy} attribute as found on AOP-related XML tags.
*/
private static final String EXPOSE_PROXY_ATTRIBUTE = "expose-proxy";
public static void registerAutoProxyCreatorIfNecessary(
ParserContext parserContext, Element sourceElement) {
BeanDefinition beanDefinition = AopConfigUtils.registerAutoProxyCreatorIfNecessary(
parserContext.getRegistry(), parserContext.extractSource(sourceElement));
useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
registerComponentIfNecessary(beanDefinition, parserContext);
}
public static void registerAspectJAutoProxyCreatorIfNecessary(
ParserContext parserContext, Element sourceElement) {
BeanDefinition beanDefinition = AopConfigUtils.registerAspectJAutoProxyCreatorIfNecessary(
parserContext.getRegistry(), parserContext.extractSource(sourceElement));
useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
registerComponentIfNecessary(beanDefinition, parserContext);
}
}
主要关注这一行,怎么拿到beanDefinition的呢?
最终是把 beanDefinition放到parserContext 中的
public abstract class AopConfigUtils {
public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, Object source) {
return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
}
private static BeanDefinition registerOrEscalateApcAsRequired(Class<?> cls, BeanDefinitionRegistry registry, Object source) {
Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {
BeanDefinition apcDefinition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);
if (!cls.getName().equals(apcDefinition.getBeanClassName())) {
int currentPriority = findPriorityForClass(apcDefinition.getBeanClassName());
int requiredPriority = findPriorityForClass(cls);
if (currentPriority < requiredPriority) {
apcDefinition.setBeanClassName(cls.getName());
}
}
return null;
}
RootBeanDefinition beanDefinition = new RootBeanDefinition(cls);
beanDefinition.setSource(source);
beanDefinition.getPropertyValues().add("order", Ordered.HIGHEST_PRECEDENCE);
beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
registry.registerBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME, beanDefinition);
return beanDefinition;
}
}
registerAutoProxyCreatorIfNecessary 主要是返回 beanDefinition的,主要需要看下InfrastructureAdvisorAutoProxyCreator.class这个类
return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
看这个类,主要关注的是bean的实例化之后干了啥postProcessAfterInitialization类
看继承关系InfrastructureAdvisorAutoProxyCreator 继承AbstractAdvisorAutoProxyCreator 继承AbstractAutoProxyCreator实现SmartInstantiationAwareBeanPostProcessor
@SuppressWarnings("serial")
public abstract class AbstractAutoProxyCreator extends ProxyProcessorSupport
implements SmartInstantiationAwareBeanPostProcessor, BeanFactoryAware {
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean != null) {
Object cacheKey = getCacheKey(bean.getClass(), beanName);
if (!this.earlyProxyReferences.contains(cacheKey)) {
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}
/**
* Wrap the given bean if necessary, i.e. if it is eligible for being proxied.
* @param bean the raw bean instance
* @param beanName the name of the bean
* @param cacheKey the cache key for metadata access
* @return a proxy wrapping the bean, or the raw bean instance as-is
*/
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
if (beanName != null && this.targetSourcedBeans.contains(beanName)) {
return bean;
}
if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
return bean;
}
if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
// Create proxy if we have advice.
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
Object proxy = createProxy(
bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
this.proxyTypes.put(cacheKey, proxy.getClass());
return proxy;
}
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
}
postProcessAfterInitialization 主要是对InfrastructureAdvisorAutoProxyCreator进行封装,封装的工作都交给 wrapIfNecessary(bean, beanName, cacheKey); 方法
看看wrapIfNecessary 怎么封装的
wrapIfNecessary 主要做了什么事情?
1. 找到指定bean对应的增强器
2.根据找到的增强器创建代理
wrapIfNecessary 怎么找到增强的?看方法getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
getAdvicesAndAdvisorsForBean方法 不仅要找到增强,还需要判断增强器是否满足要求
@SuppressWarnings("serial")
public abstract class AbstractAdvisorAutoProxyCreator extends AbstractAutoProxyCreator {
@Override
protected Object[] getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName, TargetSource targetSource) {
List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
if (advisors.isEmpty()) {
return DO_NOT_PROXY;
}
return advisors.toArray();
}
/**
* Find all eligible Advisors for auto-proxying this class.
* @param beanClass the clazz to find advisors for
* @param beanName the name of the currently proxied bean
* @return the empty List, not {@code null},
* if there are no pointcuts or interceptors
* @see #findCandidateAdvisors
* @see #sortAdvisors
* @see #extendAdvisors
*/
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
List<Advisor> candidateAdvisors = findCandidateAdvisors();
List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
extendAdvisors(eligibleAdvisors);
if (!eligibleAdvisors.isEmpty()) {
eligibleAdvisors = sortAdvisors(eligibleAdvisors);
}
return eligibleAdvisors;
}
/**
* Find all candidate Advisors to use in auto-proxying.
* @return the List of candidate Advisors
*/
protected List<Advisor> findCandidateAdvisors() {
return this.advisorRetrievalHelper.findAdvisorBeans();
}
protected List<Advisor> findAdvisorsThatCanApply(
List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {
ProxyCreationContext.setCurrentProxiedBeanName(beanName);
try {
return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
}
finally {
ProxyCreationContext.setCurrentProxiedBeanName(null);
}
}
}
使用 findCandidateAdvisors 去找增强器,然后使用findAdvisorsThatCanApply 方法从候选增强器中找到匹配项目
public abstract class AopUtils {
public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {
if (candidateAdvisors.isEmpty()) {
return candidateAdvisors;
}
List<Advisor> eligibleAdvisors = new LinkedList<Advisor>();
for (Advisor candidate : candidateAdvisors) {
if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
eligibleAdvisors.add(candidate);
}
}
boolean hasIntroductions = !eligibleAdvisors.isEmpty();
for (Advisor candidate : candidateAdvisors) {
if (candidate instanceof IntroductionAdvisor) {
// already processed
continue;
}
if (canApply(candidate, clazz, hasIntroductions)) {
eligibleAdvisors.add(candidate);
}
}
return eligibleAdvisors;
}
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 {
// It doesn't have a pointcut so we assume it applies.
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;
}
MethodMatcher methodMatcher = pc.getMethodMatcher();
if (methodMatcher == MethodMatcher.TRUE) {
// No need to iterate the methods if we're matching any method anyway...
return true;
}
IntroductionAwareMethodMatcher introductionAwareMethodMatcher = null;
if (methodMatcher instanceof IntroductionAwareMethodMatcher) {
introductionAwareMethodMatcher = (IntroductionAwareMethodMatcher) methodMatcher;
}
Set<Class<?>> classes = new LinkedHashSet<Class<?>>(ClassUtils.getAllInterfacesForClassAsSet(targetClass));
classes.add(targetClass);
for (Class<?> clazz : classes) {
Method[] methods = ReflectionUtils.getAllDeclaredMethods(clazz);
for (Method method : methods) {
if ((introductionAwareMethodMatcher != null &&
introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions)) ||
methodMatcher.matches(method, targetClass)) {
return true;
}
}
}
return false;
}
}
看methodMatcher.matchers(methmod,targetClass) 怎么匹配的
@SuppressWarnings("serial")
abstract class TransactionAttributeSourcePointcut extends StaticMethodMatcherPointcut implements Serializable {
@Override
public boolean matches(Method method, Class<?> targetClass) {
if (targetClass != null && TransactionalProxy.class.isAssignableFrom(targetClass)) {
return false;
}
TransactionAttributeSource tas = getTransactionAttributeSource();
return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
}
}
getTransactionAttributeSource()获取切点的套路是一样的 使用TransactionAttributeSource的getTransactionAttribute获取
getTransactionAttribute还是先从缓存中加载,加载不到 使用computeTransactionAttribute 去提取
class TransactionalRepositoryProxyPostProcessor implements RepositoryProxyPostProcessor {
public TransactionAttribute getTransactionAttribute(Method method, Class<?> targetClass) {
// First, see if we have a cached value.
Object cacheKey = getCacheKey(method, targetClass);
Object cached = this.attributeCache.get(cacheKey);
if (cached != null) {
// Value will either be canonical value indicating there is no transaction attribute,
// or an actual transaction attribute.
if (cached == NULL_TRANSACTION_ATTRIBUTE) {
return null;
} else {
return (TransactionAttribute) cached;
}
} else {
// We need to work it out.
TransactionAttribute txAtt = computeTransactionAttribute(method, targetClass);
// Put it in the cache.
if (txAtt == null) {
this.attributeCache.put(cacheKey, NULL_TRANSACTION_ATTRIBUTE);
} else {
if (logger.isDebugEnabled()) {
logger.debug("Adding transactional method '" + method.getName() + "' with attribute: " + txAtt);
}
this.attributeCache.put(cacheKey, txAtt);
}
return txAtt;
}
}
public TransactionAttribute getTransactionAttribute(Method method, Class<?> targetClass) {
// First, see if we have a cached value.
Object cacheKey = getCacheKey(method, targetClass);
Object cached = this.attributeCache.get(cacheKey);
if (cached != null) {
// Value will either be canonical value indicating there is no transaction attribute,
// or an actual transaction attribute.
if (cached == NULL_TRANSACTION_ATTRIBUTE) {
return null;
} else {
return (TransactionAttribute) cached;
}
} else {
// We need to work it out.
TransactionAttribute txAtt = computeTransactionAttribute(method, targetClass);
// Put it in the cache.
if (txAtt == null) {
this.attributeCache.put(cacheKey, NULL_TRANSACTION_ATTRIBUTE);
} else {
if (logger.isDebugEnabled()) {
logger.debug("Adding transactional method '" + method.getName() + "' with attribute: " + txAtt);
}
this.attributeCache.put(cacheKey, txAtt);
}
return txAtt;
}
}
private TransactionAttribute computeTransactionAttribute(Method method, Class<?> targetClass) {
// Don't allow no-public methods as required.
if (allowPublicMethodsOnly() && !Modifier.isPublic(method.getModifiers())) {
return null;
}
// Ignore CGLIB subclasses - introspect the actual user class.
Class<?> userClass = ClassUtils.getUserClass(targetClass);
// The method may be on an interface, but we need attributes from the target class. // methmod 代表接口中的方法 specificMethod 代表实现类的方法
// If the target class is null, the method will be unchanged.
Method specificMethod = ClassUtils.getMostSpecificMethod(method, userClass);
// If we are dealing with method with generic parameters, find the original method.
specificMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);
TransactionAttribute txAtt = null;
if (specificMethod != method) {
// Fallback is to look at the original method.
// 查看方法方法释放声明事务
txAtt = findTransactionAttribute(method);
if (txAtt != null) {
return txAtt;
}
// Last fallback is the class of the original method.
// 如果存在,从接口中去寻找
txAtt = findTransactionAttribute(method.getDeclaringClass());
if (txAtt != null || !enableDefaultTransactions) {
return txAtt;
}
}
// Start: Implementation class check block
// First try is the method in the target class.
txAtt = findTransactionAttribute(specificMethod);
if (txAtt != null) {
return txAtt;
}
// Second try is the transaction attribute on the target class.
txAtt = findTransactionAttribute(specificMethod.getDeclaringClass());
if (txAtt != null) {
return txAtt;
}
if (!enableDefaultTransactions) {
return null;
}
// Fallback to implementation class transaction settings of nothing found
// return findTransactionAttribute(method);
Method targetClassMethod = repositoryInformation.getTargetClassMethod(method);
if (targetClassMethod.equals(method)) {
return null;
}
txAtt = findTransactionAttribute(targetClassMethod);
if (txAtt != null) {
return txAtt;
}
txAtt = findTransactionAttribute(targetClassMethod.getDeclaringClass());
if (txAtt != null) {
return txAtt;
}
return null;
// End: Implementation class check block
}
}
再看怎么查找事务声明的
class TransactionalRepositoryProxyPostProcessor implements RepositoryProxyPostProcessor {
@Override
protected TransactionAttribute findTransactionAttribute(Class<?> clazz) {
return determineTransactionAttribute(clazz);
}
// 看到注解获取了
protected TransactionAttribute determineTransactionAttribute(AnnotatedElement ae) {
for (TransactionAnnotationParser annotationParser : this.annotationParsers) {
TransactionAttribute attr = annotationParser.parseTransactionAnnotation(ae);
if (attr != null) {
return attr;
}
}
return null;
}
}
看下Spring 注解解析器是怎么解析 注解声明的
public class SpringTransactionAnnotationParser implements TransactionAnnotationParser, Serializable {
@Override
public TransactionAttribute parseTransactionAnnotation(AnnotatedElement ae) {
AnnotationAttributes attributes = AnnotatedElementUtils.getMergedAnnotationAttributes(ae, Transactional.class);
if (attributes != null) {
return parseTransactionAnnotation(attributes);
}
else {
return null;
}
}
protected TransactionAttribute parseTransactionAnnotation(AnnotationAttributes attributes) {
RuleBasedTransactionAttribute rbta = new RuleBasedTransactionAttribute();
Propagation propagation = attributes.getEnum("propagation");
rbta.setPropagationBehavior(propagation.value());
Isolation 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<RollbackRuleAttribute>();
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;
}
}
解析完了之后事务标签之后,再回到最开始,我们是怎么实现增强的
class AnnotationDrivenBeanDefinitionParser implements BeanDefinitionParser {
private static class AopAutoProxyConfigurer {
public static void configureAutoProxyCreator(Element element, ParserContext parserContext) {
// Create the TransactionAttributeSourceAdvisor definition.
RootBeanDefinition advisorDef = new RootBeanDefinition(BeanFactoryTransactionAttributeSourceAdvisor.class);
advisorDef.setSource(eleSource);
advisorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
advisorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
advisorDef.getPropertyValues().add("adviceBeanName", interceptorName);
if (element.hasAttribute("order")) {
advisorDef.getPropertyValues().add("order", element.getAttribute("order"));
}
parserContext.getRegistry().registerBeanDefinition(txAdvisorBeanName, advisorDef);
}
}
BeanFactoryTransactionAttributeSourceAdvisor 作为增强的实现类,当代理被调用时会调用这个类的增强方法,也就是Bean的advice,在自定义标签解析时,注入的类成为了整个事务的功能基础。BeanFactoryTransactionAttributeSourceAdvisor 作为Advisor的实现类,自然要遵从Advisor的处理方式,当代理被调用是会调用这个增强方法,也就是此bean的Advise,因为在解析事务标签时,我们把TransactionInterceptor类型的bean注入到了BeanFactory TransactionInterceptor进行增强,同时也就是在TransactionInterceptor类的invoke方法中完成整个事务逻辑
public abstract class TransactionAspectSupport implements BeanFactoryAware, InitializingBean {
protected Object invokeWithinTransaction(Method method, Class<?> targetClass, final InvocationCallback invocation)
throws Throwable {
// If the transaction attribute is null, the method is non-transactional.
final TransactionAttribute txAttr = getTransactionAttributeSource().getTransactionAttribute(method, targetClass);
final PlatformTransactionManager tm = determineTransactionManager(txAttr);
final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
// Standard transaction demarcation with getTransaction and commit/rollback calls.
TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
Object retVal = null;
try {
// This is an around advice: Invoke the next interceptor in the chain.
// This will normally result in a target object being invoked.
retVal = invocation.proceedWithInvocation();
}
catch (Throwable ex) {
// target invocation exception
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
}
finally {
cleanupTransactionInfo(txInfo);
}
commitTransactionAfterReturning(txInfo);
return retVal;
}
}
综合来看
可以理解 spring aop 事务
{org.springframework.transaction.config.internalTransactionAdvisor=false}