Spring5.0源码深度解析之SpringBean声明事务底层实现原理
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
@Bean
public 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
*/
@Bean
public JdbcTemplate jdbcTemplate() {
return new JdbcTemplate(dataSource());
}
@Bean
public PlatformTransactionManager platformTransactionManager(){
return new DataSourceTransactionManager(dataSource());
}
}
@Service
public class OrderServiceImpl implements OrderService {
@Autowired
private 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) {
}
}
}
org.springframework spring-context 5.0.5.RELEASE mysql mysql-connector-java 5.1.46 org.springframework spring-jdbc 5.0.5.RELEASE
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{ @Override 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; } } }
public class AutoProxyRegistrar implements ImportBeanDefinitionRegistrar {//向IOC容器中注入Bean对象
....
@Override
public 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.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_beanName
Object 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 advisors = this.findEligibleAdvisors(beanClass, beanName);
return advisors.isEmpty() ? DO_NOT_PROXY : advisors.toArray();
}
protected ListfindEligibleAdvisors(Class beanClass, String beanName) { List candidateAdvisors = this.findCandidateAdvisors();//寻找候选增强器，这里不介绍了 ListeligibleAdvisors = this.findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);//候选增强器中寻找匹配项，这里分析下 .... }
protected ListfindAdvisorsThatCanApply(List candidateAdvisors, Class beanClass, String beanName) { .... try { var4 = AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass); .... }
public static ListfindAdvisorsThatCanApply(List 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isolation
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 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/